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pcre2test - Man Page

a program for testing Perl-compatible regular expressions.


pcre2test [options] [input file [output file]]

pcre2test is a test program for the PCRE2 regular expression libraries, but it can also be used for experimenting with regular expressions. This document describes the features of the test program; for details of the regular expressions themselves, see the pcre2pattern documentation. For details of the PCRE2 library function calls and their options, see the pcre2api documentation.

The input for pcre2test is a sequence of regular expression patterns and subject strings to be matched. There are also command lines for setting defaults and controlling some special actions. The output shows the result of each match attempt. Modifiers on external or internal command lines, the patterns, and the subject lines specify PCRE2 function options, control how the subject is processed, and what output is produced.

There are many obscure modifiers, some of which are specifically designed for use in conjunction with the test script and data files that are distributed as part of PCRE2. All the modifiers are documented here, some without much justification, but many of them are unlikely to be of use except when testing the libraries.


Different versions of the PCRE2 library can be built to support character strings that are encoded in 8-bit, 16-bit, or 32-bit code units. One, two, or all three of these libraries may be simultaneously installed. The pcre2test program can be used to test all the libraries. However, its own input and output are always in 8-bit format. When testing the 16-bit or 32-bit libraries, patterns and subject strings are converted to 16-bit or 32-bit format before being passed to the library functions. Results are converted back to 8-bit code units for output.

In the rest of this document, the names of library functions and structures are given in generic form, for example, pcre2_compile(). The actual names used in the libraries have a suffix _8, _16, or _32, as appropriate.

Input Encoding

Input to pcre2test is processed line by line, either by calling the C library's fgets() function, or via the libreadline or libedit library. In some Windows environments character 26 (hex 1A) causes an immediate end of file, and no further data is read, so this character should be avoided unless you really want that action.

The input is processed using C's string functions, so must not contain binary zeros, even though in Unix-like environments, fgets() treats any bytes other than newline as data characters. An error is generated if a binary zero is encountered. By default subject lines are processed for backslash escapes, which makes it possible to include any data value in strings that are passed to the library for matching. For patterns, there is a facility for specifying some or all of the 8-bit input characters as hexadecimal pairs, which makes it possible to include binary zeros.

Input for the 16-bit and 32-bit libraries

When testing the 16-bit or 32-bit libraries, there is a need to be able to generate character code points greater than 255 in the strings that are passed to the library. For subject lines, backslash escapes can be used. In addition, when the utf modifier (see "Setting compilation options" below) is set, the pattern and any following subject lines are interpreted as UTF-8 strings and translated to UTF-16 or UTF-32 as appropriate.

For non-UTF testing of wide characters, the utf8_input modifier can be used. This is mutually exclusive with utf, and is allowed only in 16-bit or 32-bit mode. It causes the pattern and following subject lines to be treated as UTF-8 according to the original definition (RFC 2279), which allows for character values up to 0x7fffffff. Each character is placed in one 16-bit or 32-bit code unit (in the 16-bit case, values greater than 0xffff cause an error to occur).

UTF-8 (in its original definition) is not capable of encoding values greater than 0x7fffffff, but such values can be handled by the 32-bit library. When testing this library in non-UTF mode with utf8_input set, if any character is preceded by the byte 0xff (which is an invalid byte in UTF-8) 0x80000000 is added to the character's value. This is the only way of passing such code points in a pattern string. For subject strings, using an escape sequence is preferable.

Command Line Options


If the 8-bit library has been built, this option causes it to be used (this is the default). If the 8-bit library has not been built, this option causes an error.


If the 16-bit library has been built, this option causes it to be used. If the 8-bit library has not been built, this is the default. If the 16-bit library has not been built, this option causes an error.


If the 32-bit library has been built, this option causes it to be used. If no other library has been built, this is the default. If the 32-bit library has not been built, this option causes an error.


Behave as if each pattern has the auto_callout modifier, that is, insert automatic callouts into every pattern that is compiled.


As for -ac, but in addition behave as if each subject line has the callout_extra modifier, that is, show additional information from callouts.


Behave as if each pattern has the fullbincode modifier; the full internal binary form of the pattern is output after compilation.


Output the version number of the PCRE2 library, and all available information about the optional features that are included, and then exit with zero exit code. All other options are ignored. If both -C and -LM are present, whichever is first is recognized.

-C option

Output information about a specific build-time option, then exit. This functionality is intended for use in scripts such as RunTest. The following options output the value and set the exit code as indicated:

 ebcdic-nl  the code for LF (= NL) in an EBCDIC environment:
              0x15 or 0x25
              0 if used in an ASCII environment
              exit code is always 0
 linksize   the configured internal link size (2, 3, or 4)
              exit code is set to the link size
 newline    the default newline setting:
              CR, LF, CRLF, ANYCRLF, ANY, or NUL
              exit code is always 0
 bsr        the default setting for what \R matches:
              ANYCRLF or ANY
              exit code is always 0

The following options output 1 for true or 0 for false, and set the exit code to the same value:

 backslash-C  \C is supported (not locked out)
 ebcdic       compiled for an EBCDIC environment
 jit          just-in-time support is available
 pcre2-16     the 16-bit library was built
 pcre2-32     the 32-bit library was built
 pcre2-8      the 8-bit library was built
 unicode      Unicode support is available

If an unknown option is given, an error message is output; the exit code is 0.


Behave as if each pattern has the debug modifier; the internal form and information about the compiled pattern is output after compilation; -d is equivalent to -b -i.


Behave as if each subject line has the dfa modifier; matching is done using the pcre2_dfa_match() function instead of the default pcre2_match().

-error number[,number,...]

Call pcre2_get_error_message() for each of the error numbers in the comma-separated list, display the resulting messages on the standard output, then exit with zero exit code. The numbers may be positive or negative. This is a convenience facility for PCRE2 maintainers.


Output a brief summary these options and then exit.


Behave as if each pattern has the info modifier; information about the compiled pattern is given after compilation.


Behave as if each pattern line has the jit modifier; after successful compilation, each pattern is passed to the just-in-time compiler, if available.


Behave as if each pattern line has the jitfast modifier; after successful compilation, each pattern is passed to the just-in-time compiler, if available, and each subject line is passed directly to the JIT matcher via its "fast path".


Behave as if each pattern line has the jitverify modifier; after successful compilation, each pattern is passed to the just-in-time compiler, if available, and the use of JIT for matching is verified.


List modifiers: write a list of available pattern and subject modifiers to the standard output, then exit with zero exit code. All other options are ignored. If both -C and any -Lx options are present, whichever is first is recognized.


List properties: write a list of recognized Unicode properties to the standard output, then exit with zero exit code. All other options are ignored. If both -C and any -Lx options are present, whichever is first is recognized.


List scripts: write a list of recognized Unicode script names to the standard output, then exit with zero exit code. All other options are ignored. If both -C and any -Lx options are present, whichever is first is recognized.

-pattern modifier-list

Behave as if each pattern line contains the given modifiers.


Do not output the version number of pcre2test at the start of execution.

-S size

On Unix-like systems, set the size of the run-time stack to size mebibytes (units of 1024*1024 bytes).

-subject modifier-list

Behave as if each subject line contains the given modifiers.


Run each compile and match many times with a timer, and output the resulting times per compile or match. When JIT is used, separate times are given for the initial compile and the JIT compile. You can control the number of iterations that are used for timing by following -t with a number (as a separate item on the command line). For example, "-t 1000" iterates 1000 times. The default is to iterate 500,000 times.


This is like -t except that it times only the matching phase, not the compile phase.

-T -TM

These behave like -t and -tm, but in addition, at the end of a run, the total times for all compiles and matches are output.


Output the PCRE2 version number and then exit.


If pcre2test is given two filename arguments, it reads from the first and writes to the second. If the first name is "-", input is taken from the standard input. If pcre2test is given only one argument, it reads from that file and writes to stdout. Otherwise, it reads from stdin and writes to stdout.

When pcre2test is built, a configuration option can specify that it should be linked with the libreadline or libedit library. When this is done, if the input is from a terminal, it is read using the readline() function. This provides line-editing and history facilities. The output from the -help option states whether or not readline() will be used.

The program handles any number of tests, each of which consists of a set of input lines. Each set starts with a regular expression pattern, followed by any number of subject lines to be matched against that pattern. In between sets of test data, command lines that begin with # may appear. This file format, with some restrictions, can also be processed by the perltest.sh script that is distributed with PCRE2 as a means of checking that the behaviour of PCRE2 and Perl is the same. For a specification of perltest.sh, see the comments near its beginning. See also the #perltest command below.

When the input is a terminal, pcre2test prompts for each line of input, using "re>" to prompt for regular expression patterns, and "data>" to prompt for subject lines. Command lines starting with # can be entered only in response to the "re>" prompt.

Each subject line is matched separately and independently. If you want to do multi-line matches, you have to use the \n escape sequence (or \r or \r\n, etc., depending on the newline setting) in a single line of input to encode the newline sequences. There is no limit on the length of subject lines; the input buffer is automatically extended if it is too small. There are replication features that makes it possible to generate long repetitive pattern or subject lines without having to supply them explicitly.

An empty line or the end of the file signals the end of the subject lines for a test, at which point a new pattern or command line is expected if there is still input to be read.

Command Lines

In between sets of test data, a line that begins with # is interpreted as a command line. If the first character is followed by white space or an exclamation mark, the line is treated as a comment, and ignored. Otherwise, the following commands are recognized:


Subsequent patterns automatically have the PCRE2_NEVER_UTF and PCRE2_NEVER_UCP options set, which locks out the use of the PCRE2_UTF and PCRE2_UCP options and the use of (*UTF) and (*UCP) at the start of patterns. This command also forces an error if a subsequent pattern contains any occurrences of \P, \p, or \X, which are still supported when PCRE2_UTF is not set, but which require Unicode property support to be included in the library.

This is a trigger guard that is used in test files to ensure that UTF or Unicode property tests are not accidentally added to files that are used when Unicode support is not included in the library. Setting PCRE2_NEVER_UTF and PCRE2_NEVER_UCP as a default can also be obtained by the use of #pattern; the difference is that #forbid_utf cannot be unset, and the automatic options are not displayed in pattern information, to avoid cluttering up test output.

 #load <filename>

This command is used to load a set of precompiled patterns from a file, as described in the section entitled "Saving and restoring compiled patterns" below.

 #loadtables <filename>

This command is used to load a set of binary character tables that can be accessed by the tables=3 qualifier. Such tables can be created by the pcre2_dftables program with the -b option.

 #newline_default [<newline-list>]

When PCRE2 is built, a default newline convention can be specified. This determines which characters and/or character pairs are recognized as indicating a newline in a pattern or subject string. The default can be overridden when a pattern is compiled. The standard test files contain tests of various newline conventions, but the majority of the tests expect a single linefeed to be recognized as a newline by default. Without special action the tests would fail when PCRE2 is compiled with either CR or CRLF as the default newline.

The #newline_default command specifies a list of newline types that are acceptable as the default. The types must be one of CR, LF, CRLF, ANYCRLF, ANY, or NUL (in upper or lower case), for example:

 #newline_default LF Any anyCRLF

If the default newline is in the list, this command has no effect. Otherwise, except when testing the POSIX API, a newline modifier that specifies the first newline convention in the list (LF in the above example) is added to any pattern that does not already have a newline modifier. If the newline list is empty, the feature is turned off. This command is present in a number of the standard test input files.

When the POSIX API is being tested there is no way to override the default newline convention, though it is possible to set the newline convention from within the pattern. A warning is given if the posix or posix_nosub modifier is used when #newline_default would set a default for the non-POSIX API.

 #pattern <modifier-list>

This command sets a default modifier list that applies to all subsequent patterns. Modifiers on a pattern can change these settings.


This line is used in test files that can also be processed by perltest.sh to confirm that Perl gives the same results as PCRE2. Subsequent tests are checked for the use of pcre2test features that are incompatible with the perltest.sh script.

Patterns must use '/' as their delimiter, and only certain modifiers are supported. Comment lines, #pattern commands, and #subject commands that set or unset "mark" are recognized and acted on. The #perltest, #forbid_utf, and #newline_default commands, which are needed in the relevant pcre2test files, are silently ignored. All other command lines are ignored, but give a warning message. The #perltest command helps detect tests that are accidentally put in the wrong file or use the wrong delimiter. For more details of the perltest.sh script see the comments it contains.

 #pop [<modifiers>]
 #popcopy [<modifiers>]

These commands are used to manipulate the stack of compiled patterns, as described in the section entitled "Saving and restoring compiled patterns" below.

 #save <filename>

This command is used to save a set of compiled patterns to a file, as described in the section entitled "Saving and restoring compiled patterns" below.

 #subject <modifier-list>

This command sets a default modifier list that applies to all subsequent subject lines. Modifiers on a subject line can change these settings.

Modifier Syntax

Modifier lists are used with both pattern and subject lines. Items in a list are separated by commas followed by optional white space. Trailing whitespace in a modifier list is ignored. Some modifiers may be given for both patterns and subject lines, whereas others are valid only for one or the other. Each modifier has a long name, for example "anchored", and some of them must be followed by an equals sign and a value, for example, "offset=12". Values cannot contain comma characters, but may contain spaces. Modifiers that do not take values may be preceded by a minus sign to turn off a previous setting.

A few of the more common modifiers can also be specified as single letters, for example "i" for "caseless". In documentation, following the Perl convention, these are written with a slash ("the /i modifier") for clarity. Abbreviated modifiers must all be concatenated in the first item of a modifier list. If the first item is not recognized as a long modifier name, it is interpreted as a sequence of these abbreviations. For example:


This is a pattern line whose modifier list starts with two one-letter modifiers (/i and /g). The lower-case abbreviated modifiers are the same as used in Perl.

Pattern Syntax

A pattern line must start with one of the following characters (common symbols, excluding pattern meta-characters):

 / ! " ' ` - = _ : ; , % & @ ~

This is interpreted as the pattern's delimiter. A regular expression may be continued over several input lines, in which case the newline characters are included within it. It is possible to include the delimiter as a literal within the pattern by escaping it with a backslash, for example


If you do this, the escape and the delimiter form part of the pattern, but since the delimiters are all non-alphanumeric, the inclusion of the backslash does not affect the pattern's interpretation. Note, however, that this trick does not work within \Q...\E literal bracketing because the backslash will itself be interpreted as a literal. If the terminating delimiter is immediately followed by a backslash, for example,


a backslash is added to the end of the pattern. This is done to provide a way of testing the error condition that arises if a pattern finishes with a backslash, because


is interpreted as the first line of a pattern that starts with "abc/", causing pcre2test to read the next line as a continuation of the regular expression.

A pattern can be followed by a modifier list (details below).

Subject Line Syntax

Before each subject line is passed to pcre2_match(), pcre2_dfa_match(), or pcre2_jit_match(), leading and trailing white space is removed, and the line is scanned for backslash escapes, unless the subject_literal modifier was set for the pattern. The following provide a means of encoding non-printing characters in a visible way:

 \a         alarm (BEL, \x07)
 \b         backspace (\x08)
 \e         escape (\x27)
 \f         form feed (\x0c)
 \n         newline (\x0a)
 \r         carriage return (\x0d)
 \t         tab (\x09)
 \v         vertical tab (\x0b)
 \nnn       octal character (up to 3 octal digits); always
              a byte unless > 255 in UTF-8 or 16-bit or 32-bit mode
 \o{dd...}  octal character (any number of octal digits}
 \xhh       hexadecimal byte (up to 2 hex digits)
 \x{hh...}  hexadecimal character (any number of hex digits)

The use of \x{hh...} is not dependent on the use of the utf modifier on the pattern. It is recognized always. There may be any number of hexadecimal digits inside the braces; invalid values provoke error messages.

Note that \xhh specifies one byte rather than one character in UTF-8 mode; this makes it possible to construct invalid UTF-8 sequences for testing purposes. On the other hand, \x{hh} is interpreted as a UTF-8 character in UTF-8 mode, generating more than one byte if the value is greater than 127. When testing the 8-bit library not in UTF-8 mode, \x{hh} generates one byte for values less than 256, and causes an error for greater values.

In UTF-16 mode, all 4-digit \x{hhhh} values are accepted. This makes it possible to construct invalid UTF-16 sequences for testing purposes.

In UTF-32 mode, all 4- to 8-digit \x{...} values are accepted. This makes it possible to construct invalid UTF-32 sequences for testing purposes.

There is a special backslash sequence that specifies replication of one or more characters:


This makes it possible to test long strings without having to provide them as part of the file. For example:


is converted to "abcabcabcabc". This feature does not support nesting. To include a closing square bracket in the characters, code it as \x5D.

A backslash followed by an equals sign marks the end of the subject string and the start of a modifier list. For example:


If the subject string is empty and \= is followed by whitespace, the line is treated as a comment line, and is not used for matching. For example:

 \= This is a comment.
 abc\= This is an invalid modifier list.

A backslash followed by any other non-alphanumeric character just escapes that character. A backslash followed by anything else causes an error. However, if the very last character in the line is a backslash (and there is no modifier list), it is ignored. This gives a way of passing an empty line as data, since a real empty line terminates the data input.

If the subject_literal modifier is set for a pattern, all subject lines that follow are treated as literals, with no special treatment of backslashes. No replication is possible, and any subject modifiers must be set as defaults by a #subject command.

Pattern Modifiers

There are several types of modifier that can appear in pattern lines. Except where noted below, they may also be used in #pattern commands. A pattern's modifier list can add to or override default modifiers that were set by a previous #pattern command.

Setting compilation options

The following modifiers set options for pcre2_compile(). Most of them set bits in the options argument of that function, but those whose names start with PCRE2_EXTRA are additional options that are set in the compile context. Some of these options have single-letter abbreviations. There is special handling for /x: if a second x is present, PCRE2_EXTENDED is converted into PCRE2_EXTENDED_MORE as in Perl. A third appearance adds PCRE2_EXTENDED as well, though this makes no difference to the way pcre2_compile() behaves. See pcre2api for a description of the effects of these options.

     allow_empty_class         set PCRE2_ALLOW_EMPTY_CLASS
     allow_lookaround_bsk      set PCRE2_EXTRA_ALLOW_LOOKAROUND_BSK
     allow_surrogate_escapes   set PCRE2_EXTRA_ALLOW_SURROGATE_ESCAPES
     alt_bsux                  set PCRE2_ALT_BSUX
     alt_circumflex            set PCRE2_ALT_CIRCUMFLEX
     alt_verbnames             set PCRE2_ALT_VERBNAMES
     anchored                  set PCRE2_ANCHORED
 /a  ascii_all                 set all ASCII options
     ascii_bsd                 set PCRE2_EXTRA_ASCII_BSD
     ascii_bss                 set PCRE2_EXTRA_ASCII_BSS
     ascii_bsw                 set PCRE2_EXTRA_ASCII_BSW
     ascii_digit               set PCRE2_EXTRA_ASCII_DIGIT
     ascii_posix               set PCRE2_EXTRA_ASCII_POSIX
     auto_callout              set PCRE2_AUTO_CALLOUT
     bad_escape_is_literal     set PCRE2_EXTRA_BAD_ESCAPE_IS_LITERAL
 /i  caseless                  set PCRE2_CASELESS
 /r  caseless_restrict         set PCRE2_EXTRA_CASELESS_RESTRICT
     dollar_endonly            set PCRE2_DOLLAR_ENDONLY
 /s  dotall                    set PCRE2_DOTALL
     dupnames                  set PCRE2_DUPNAMES
     endanchored               set PCRE2_ENDANCHORED
     escaped_cr_is_lf          set PCRE2_EXTRA_ESCAPED_CR_IS_LF
 /x  extended                  set PCRE2_EXTENDED
 /xx extended_more             set PCRE2_EXTENDED_MORE
     extra_alt_bsux            set PCRE2_EXTRA_ALT_BSUX
     firstline                 set PCRE2_FIRSTLINE
     literal                   set PCRE2_LITERAL
     match_line                set PCRE2_EXTRA_MATCH_LINE
     match_invalid_utf         set PCRE2_MATCH_INVALID_UTF
     match_unset_backref       set PCRE2_MATCH_UNSET_BACKREF
     match_word                set PCRE2_EXTRA_MATCH_WORD
 /m  multiline                 set PCRE2_MULTILINE
     never_backslash_c         set PCRE2_NEVER_BACKSLASH_C
     never_ucp                 set PCRE2_NEVER_UCP
     never_utf                 set PCRE2_NEVER_UTF
 /n  no_auto_capture           set PCRE2_NO_AUTO_CAPTURE
     no_auto_possess           set PCRE2_NO_AUTO_POSSESS
     no_dotstar_anchor         set PCRE2_NO_DOTSTAR_ANCHOR
     no_start_optimize         set PCRE2_NO_START_OPTIMIZE
     no_utf_check              set PCRE2_NO_UTF_CHECK
     ucp                       set PCRE2_UCP
     ungreedy                  set PCRE2_UNGREEDY
     use_offset_limit          set PCRE2_USE_OFFSET_LIMIT
     utf                       set PCRE2_UTF

As well as turning on the PCRE2_UTF option, the utf modifier causes all non-printing characters in output strings to be printed using the \x{hh...} notation. Otherwise, those less than 0x100 are output in hex without the curly brackets. Setting utf in 16-bit or 32-bit mode also causes pattern and subject strings to be translated to UTF-16 or UTF-32, respectively, before being passed to library functions.

Setting compilation controls

The following modifiers affect the compilation process or request information about the pattern. There are single-letter abbreviations for some that are heavily used in the test files.

     bsr=[anycrlf|unicode]     specify \R handling
 /B  bincode                   show binary code without lengths
     callout_info              show callout information
     convert=<options>         request foreign pattern conversion
     convert_glob_escape=c     set glob escape character
     convert_glob_separator=c  set glob separator character
     convert_length            set convert buffer length
     debug                     same as info,fullbincode
     framesize                 show matching frame size
     fullbincode               show binary code with lengths
 /I  info                      show info about compiled pattern
     hex                       unquoted characters are hexadecimal
     jit[=<number>]            use JIT
     jitfast                   use JIT fast path
     jitverify                 verify JIT use
     locale=<name>             use this locale
     max_pattern_compiled      ) set maximum compiled pattern
                _length=<n>    )   length (bytes)
     max_pattern_length=<n>    set maximum pattern length (code units)
     max_varlookbehind=<n>     set maximum variable lookbehind length
     memory                    show memory used
     newline=<type>            set newline type
     null_context              compile with a NULL context
     null_pattern              pass pattern as NULL
     parens_nest_limit=<n>     set maximum parentheses depth
     posix                     use the POSIX API
     posix_nosub               use the POSIX API with REG_NOSUB
     push                      push compiled pattern onto the stack
     pushcopy                  push a copy onto the stack
     stackguard=<number>       test the stackguard feature
     subject_literal           treat all subject lines as literal
     tables=[0|1|2|3]          select internal tables
     use_length                do not zero-terminate the pattern
     utf8_input                treat input as UTF-8

The effects of these modifiers are described in the following sections.

Newline and \R handling

The bsr modifier specifies what \R in a pattern should match. If it is set to "anycrlf", \R matches CR, LF, or CRLF only. If it is set to "unicode", \R matches any Unicode newline sequence. The default can be specified when PCRE2 is built; if it is not, the default is set to Unicode.

The newline modifier specifies which characters are to be interpreted as newlines, both in the pattern and in subject lines. The type must be one of CR, LF, CRLF, ANYCRLF, ANY, or NUL (in upper or lower case).

Information about a pattern

The debug modifier is a shorthand for info,fullbincode, requesting all available information.

The bincode modifier causes a representation of the compiled code to be output after compilation. This information does not contain length and offset values, which ensures that the same output is generated for different internal link sizes and different code unit widths. By using bincode, the same regression tests can be used in different environments.

The fullbincode modifier, by contrast, does include length and offset values. This is used in a few special tests that run only for specific code unit widths and link sizes, and is also useful for one-off tests.

The info modifier requests information about the compiled pattern (whether it is anchored, has a fixed first character, and so on). The information is obtained from the pcre2_pattern_info() function. Here are some typical examples:

   re> /(?i)(^a|^b)/m,info
 Capture group count = 1
 Compile options: multiline
 Overall options: caseless multiline
 First code unit at start or follows newline
 Subject length lower bound = 1

   re> /(?i)abc/info
 Capture group count = 0
 Compile options: <none>
 Overall options: caseless
 First code unit = 'a' (caseless)
 Last code unit = 'c' (caseless)
 Subject length lower bound = 3

"Compile options" are those specified by modifiers; "overall options" have added options that are taken or deduced from the pattern. If both sets of options are the same, just a single "options" line is output; if there are no options, the line is omitted. "First code unit" is where any match must start; if there is more than one they are listed as "starting code units". "Last code unit" is the last literal code unit that must be present in any match. This is not necessarily the last character. These lines are omitted if no starting or ending code units are recorded. The subject length line is omitted when no_start_optimize is set because the minimum length is not calculated when it can never be used.

The framesize modifier shows the size, in bytes, of each storage frame used by pcre2_match() for handling backtracking. The size depends on the number of capturing parentheses in the pattern. A vector of these frames is used at matching time; its overall size is shown when the heaframes_size subject modifier is set.

The callout_info modifier requests information about all the callouts in the pattern. A list of them is output at the end of any other information that is requested. For each callout, either its number or string is given, followed by the item that follows it in the pattern.

Passing a NULL context

Normally, pcre2test passes a context block to pcre2_compile(). If the null_context modifier is set, however, NULL is passed. This is for testing that pcre2_compile() behaves correctly in this case (it uses default values).

Passing a NULL pattern

The null_pattern modifier is for testing the behaviour of pcre2_compile() when the pattern argument is NULL. The length value passed is the default PCRE2_ZERO_TERMINATED unless use_length is set. Any length other than zero causes an error.

Specifying pattern characters in hexadecimal

The hex modifier specifies that the characters of the pattern, except for substrings enclosed in single or double quotes, are to be interpreted as pairs of hexadecimal digits. This feature is provided as a way of creating patterns that contain binary zeros and other non-printing characters. White space is permitted between pairs of digits. For example, this pattern contains three characters:

 /ab 32 59/hex

Parts of such a pattern are taken literally if quoted. This pattern contains nine characters, only two of which are specified in hexadecimal:

 /ab "literal" 32/hex

Either single or double quotes may be used. There is no way of including the delimiter within a substring. The hex and expand modifiers are mutually exclusive.

Specifying the pattern's length

By default, patterns are passed to the compiling functions as zero-terminated strings but can be passed by length instead of being zero-terminated. The use_length modifier causes this to happen. Using a length happens automatically (whether or not use_length is set) when hex is set, because patterns specified in hexadecimal may contain binary zeros.

If hex or use_length is used with the POSIX wrapper API (see "Using the POSIX wrapper API" below), the REG_PEND extension is used to pass the pattern's length.

Specifying a maximum for variable lookbehinds

Variable lookbehind assertions are supported only if, for each one, there is a maximum length (in characters) that it can match. There is a limit on this, whose default can be set at build time, with an ultimate default of 255. The max_varlookbehind modifier uses the pcre2_set_max_varlookbehind() function to change the limit. Lookbehinds whose branches each match a fixed length are limited to 65535 characters per branch.

Specifying wide characters in 16-bit and 32-bit modes

In 16-bit and 32-bit modes, all input is automatically treated as UTF-8 and translated to UTF-16 or UTF-32 when the utf modifier is set. For testing the 16-bit and 32-bit libraries in non-UTF mode, the utf8_input modifier can be used. It is mutually exclusive with utf. Input lines are interpreted as UTF-8 as a means of specifying wide characters. More details are given in "Input encoding" above.

Generating long repetitive patterns

Some tests use long patterns that are very repetitive. Instead of creating a very long input line for such a pattern, you can use a special repetition feature, similar to the one described for subject lines above. If the expand modifier is present on a pattern, parts of the pattern that have the form


are expanded before the pattern is passed to pcre2_compile(). For example, \[AB]{6000} is expanded to "ABAB..." 6000 times. This construction cannot be nested. An initial "\[" sequence is recognized only if "]{" followed by decimal digits and "}" is found later in the pattern. If not, the characters remain in the pattern unaltered. The expand and hex modifiers are mutually exclusive.

If part of an expanded pattern looks like an expansion, but is really part of the actual pattern, unwanted expansion can be avoided by giving two values in the quantifier. For example, \[AB]{6000,6000} is not recognized as an expansion item.

If the info modifier is set on an expanded pattern, the result of the expansion is included in the information that is output.

JIT compilation

Just-in-time (JIT) compiling is a heavyweight optimization that can greatly speed up pattern matching. See the pcre2jit documentation for details. JIT compiling happens, optionally, after a pattern has been successfully compiled into an internal form. The JIT compiler converts this to optimized machine code. It needs to know whether the match-time options PCRE2_PARTIAL_HARD and PCRE2_PARTIAL_SOFT are going to be used, because different code is generated for the different cases. See the partial modifier in "Subject Modifiers" below for details of how these options are specified for each match attempt.

JIT compilation is requested by the jit pattern modifier, which may optionally be followed by an equals sign and a number in the range 0 to 7. The three bits that make up the number specify which of the three JIT operating modes are to be compiled:

 1  compile JIT code for non-partial matching
 2  compile JIT code for soft partial matching
 4  compile JIT code for hard partial matching

The possible values for the jit modifier are therefore:

 0  disable JIT
 1  normal matching only
 2  soft partial matching only
 3  normal and soft partial matching
 4  hard partial matching only
 6  soft and hard partial matching only
 7  all three modes

If no number is given, 7 is assumed. The phrase "partial matching" means a call to pcre2_match() with either the PCRE2_PARTIAL_SOFT or the PCRE2_PARTIAL_HARD option set. Note that such a call may return a complete match; the options enable the possibility of a partial match, but do not require it. Note also that if you request JIT compilation only for partial matching (for example, jit=2) but do not set the partial modifier on a subject line, that match will not use JIT code because none was compiled for non-partial matching.

If JIT compilation is successful, the compiled JIT code will automatically be used when an appropriate type of match is run, except when incompatible run-time options are specified. For more details, see the pcre2jit documentation. See also the jitstack modifier below for a way of setting the size of the JIT stack.

If the jitfast modifier is specified, matching is done using the JIT "fast path" interface, pcre2_jit_match(), which skips some of the sanity checks that are done by pcre2_match(), and of course does not work when JIT is not supported. If jitfast is specified without jit, jit=7 is assumed.

If the jitverify modifier is specified, information about the compiled pattern shows whether JIT compilation was or was not successful. If jitverify is specified without jit, jit=7 is assumed. If JIT compilation is successful when jitverify is set, the text "(JIT)" is added to the first output line after a match or non match when JIT-compiled code was actually used in the match.

Setting a locale

The locale modifier must specify the name of a locale, for example:


The given locale is set, pcre2_maketables() is called to build a set of character tables for the locale, and this is then passed to pcre2_compile() when compiling the regular expression. The same tables are used when matching the following subject lines. The locale modifier applies only to the pattern on which it appears, but can be given in a #pattern command if a default is needed. Setting a locale and alternate character tables are mutually exclusive.

Showing pattern memory

The memory modifier causes the size in bytes of the memory used to hold the compiled pattern to be output. This does not include the size of the pcre2_code block; it is just the actual compiled data. If the pattern is subsequently passed to the JIT compiler, the size of the JIT compiled code is also output. Here is an example:

   re> /a(b)c/jit,memory
 Memory allocation (code space): 21
 Memory allocation (JIT code): 1910

Limiting nested parentheses

The parens_nest_limit modifier sets a limit on the depth of nested parentheses in a pattern. Breaching the limit causes a compilation error. The default for the library is set when PCRE2 is built, but pcre2test sets its own default of 220, which is required for running the standard test suite.

Limiting the pattern length

The max_pattern_length modifier sets a limit, in code units, to the length of pattern that pcre2_compile() will accept. Breaching the limit causes a compilation error. The default is the largest number a PCRE2_SIZE variable can hold (essentially unlimited).

Limiting the size of a compiled pattern

The max_pattern_compiled_length modifier sets a limit, in bytes, to the amount of memory used by a compiled pattern. Breaching the limit causes a compilation error. The default is the largest number a PCRE2_SIZE variable can hold (essentially unlimited).

Using the POSIX wrapper API

The posix and posix_nosub modifiers cause pcre2test to call PCRE2 via the POSIX wrapper API rather than its native API. When posix_nosub is used, the POSIX option REG_NOSUB is passed to regcomp(). The POSIX wrapper supports only the 8-bit library. Note that it does not imply POSIX matching semantics; for more detail see the pcre2posix documentation. The following pattern modifiers set options for the regcomp() function:

 caseless           REG_ICASE
 multiline          REG_NEWLINE
 dotall             REG_DOTALL     )
 ungreedy           REG_UNGREEDY   ) These options are not part of
 ucp                REG_UCP        )   the POSIX standard
 utf                REG_UTF8       )

The regerror_buffsize modifier specifies a size for the error buffer that is passed to regerror() in the event of a compilation error. For example:


This provides a means of testing the behaviour of regerror() when the buffer is too small for the error message. If this modifier has not been set, a large buffer is used.

The aftertext and allaftertext subject modifiers work as described below. All other modifiers are either ignored, with a warning message, or cause an error.

The pattern is passed to regcomp() as a zero-terminated string by default, but if the use_length or hex modifiers are set, the REG_PEND extension is used to pass it by length.

Testing the stack guard feature

The stackguard modifier is used to test the use of pcre2_set_compile_recursion_guard(), a function that is provided to enable stack availability to be checked during compilation (see the pcre2api documentation for details). If the number specified by the modifier is greater than zero, pcre2_set_compile_recursion_guard() is called to set up callback from pcre2_compile() to a local function. The argument it receives is the current nesting parenthesis depth; if this is greater than the value given by the modifier, non-zero is returned, causing the compilation to be aborted.

Using alternative character tables

The value specified for the tables modifier must be one of the digits 0, 1, 2, or 3. It causes a specific set of built-in character tables to be passed to pcre2_compile(). This is used in the PCRE2 tests to check behaviour with different character tables. The digit specifies the tables as follows:

 0   do not pass any special character tables
 1   the default ASCII tables, as distributed in
 2   a set of tables defining ISO 8859 characters
 3   a set of tables loaded by the #loadtables command

In tables 2, some characters whose codes are greater than 128 are identified as letters, digits, spaces, etc. Tables 3 can be used only after a #loadtables command has loaded them from a binary file. Setting alternate character tables and a locale are mutually exclusive.

Setting certain match controls

The following modifiers are really subject modifiers, and are described under "Subject Modifiers" below. However, they may be included in a pattern's modifier list, in which case they are applied to every subject line that is processed with that pattern. These modifiers do not affect the compilation process.

     aftertext                   show text after match
     allaftertext                show text after captures
     allcaptures                 show all captures
     allvector                   show the entire ovector
     allusedtext                 show all consulted text
     altglobal                   alternative global matching
 /g  global                      global matching
     heapframes_size             show match data heapframes size
     jitstack=<n>                set size of JIT stack
     mark                        show mark values
     replace=<string>            specify a replacement string
     startchar                   show starting character when relevant
     substitute_callout          use substitution callouts
     substitute_extended         use PCRE2_SUBSTITUTE_EXTENDED
     substitute_literal          use PCRE2_SUBSTITUTE_LITERAL
     substitute_matched          use PCRE2_SUBSTITUTE_MATCHED
     substitute_overflow_length  use PCRE2_SUBSTITUTE_OVERFLOW_LENGTH
     substitute_replacement_only use PCRE2_SUBSTITUTE_REPLACEMENT_ONLY
     substitute_skip=<n>         skip substitution <n>
     substitute_stop=<n>         skip substitution <n> and following
     substitute_unknown_unset    use PCRE2_SUBSTITUTE_UNKNOWN_UNSET
     substitute_unset_empty      use PCRE2_SUBSTITUTE_UNSET_EMPTY

These modifiers may not appear in a #pattern command. If you want them as defaults, set them in a #subject command.

Specifying literal subject lines

If the subject_literal modifier is present on a pattern, all the subject lines that it matches are taken as literal strings, with no interpretation of backslashes. It is not possible to set subject modifiers on such lines, but any that are set as defaults by a #subject command are recognized.

Saving a compiled pattern

When a pattern with the push modifier is successfully compiled, it is pushed onto a stack of compiled patterns, and pcre2test expects the next line to contain a new pattern (or a command) instead of a subject line. This facility is used when saving compiled patterns to a file, as described in the section entitled "Saving and restoring compiled patterns" below. If pushcopy is used instead of push, a copy of the compiled pattern is stacked, leaving the original as current, ready to match the following input lines. This provides a way of testing the pcre2_code_copy() function. The push and pushcopy modifiers are incompatible with compilation modifiers such as global that act at match time. Any that are specified are ignored (for the stacked copy), with a warning message, except for replace, which causes an error. Note that jitverify, which is allowed, does not carry through to any subsequent matching that uses a stacked pattern.

Testing foreign pattern conversion

The experimental foreign pattern conversion functions in PCRE2 can be tested by setting the convert modifier. Its argument is a colon-separated list of options, which set the equivalent option for the pcre2_pattern_convert() function:

 glob                    PCRE2_CONVERT_GLOB
 glob_no_starstar        PCRE2_CONVERT_GLOB_NO_STARSTAR
 glob_no_wild_separator  PCRE2_CONVERT_GLOB_NO_WILD_SEPARATOR
 posix_basic             PCRE2_CONVERT_POSIX_BASIC
 posix_extended          PCRE2_CONVERT_POSIX_EXTENDED
 unset                   Unset all options

The "unset" value is useful for turning off a default that has been set by a #pattern command. When one of these options is set, the input pattern is passed to pcre2_pattern_convert(). If the conversion is successful, the result is reflected in the output and then passed to pcre2_compile(). The normal utf and no_utf_check options, if set, cause the PCRE2_CONVERT_UTF and PCRE2_CONVERT_NO_UTF_CHECK options to be passed to pcre2_pattern_convert().

By default, the conversion function is allowed to allocate a buffer for its output. However, if the convert_length modifier is set to a value greater than zero, pcre2test passes a buffer of the given length. This makes it possible to test the length check.

The convert_glob_escape and convert_glob_separator modifiers can be used to specify the escape and separator characters for glob processing, overriding the defaults, which are operating-system dependent.

Subject Modifiers

The modifiers that can appear in subject lines and the #subject command are of two types.

Setting match options

The following modifiers set options for pcre2_match() or pcre2_dfa_match(). See pcreapi for a description of their effects.

     anchored                   set PCRE2_ANCHORED
     endanchored                set PCRE2_ENDANCHORED
     dfa_restart                set PCRE2_DFA_RESTART
     dfa_shortest               set PCRE2_DFA_SHORTEST
     disable_recurseloop_check  set PCRE2_DISABLE_RECURSELOOP_CHECK
     no_jit                     set PCRE2_NO_JIT
     no_utf_check               set PCRE2_NO_UTF_CHECK
     notbol                     set PCRE2_NOTBOL
     notempty                   set PCRE2_NOTEMPTY
     notempty_atstart           set PCRE2_NOTEMPTY_ATSTART
     noteol                     set PCRE2_NOTEOL
     partial_hard (or ph)       set PCRE2_PARTIAL_HARD
     partial_soft (or ps)       set PCRE2_PARTIAL_SOFT

The partial matching modifiers are provided with abbreviations because they appear frequently in tests.

If the posix or posix_nosub modifier was present on the pattern, causing the POSIX wrapper API to be used, the only option-setting modifiers that have any effect are notbol, notempty, and noteol, causing REG_NOTBOL, REG_NOTEMPTY, and REG_NOTEOL, respectively, to be passed to regexec(). The other modifiers are ignored, with a warning message.

There is one additional modifier that can be used with the POSIX wrapper. It is ignored (with a warning) if used for non-POSIX matching.


This causes the subject string to be passed to regexec() using the REG_STARTEND option, which uses offsets to specify which part of the string is searched. If only one number is given, the end offset is passed as the end of the subject string. For more detail of REG_STARTEND, see the pcre2posix documentation. If the subject string contains binary zeros (coded as escapes such as \x{00} because pcre2test does not support actual binary zeros in its input), you must use posix_startend to specify its length.

Setting match controls

The following modifiers affect the matching process or request additional information. Some of them may also be specified on a pattern line (see above), in which case they apply to every subject line that is matched against that pattern, but can be overridden by modifiers on the subject.

     aftertext                  show text after match
     allaftertext               show text after captures
     allcaptures                show all captures
     allvector                  show the entire ovector
     allusedtext                show all consulted text (non-JIT only)
     altglobal                  alternative global matching
     callout_capture            show captures at callout time
     callout_data=<n>           set a value to pass via callouts
     callout_error=<n>[:<m>]    control callout error
     callout_extra              show extra callout information
     callout_fail=<n>[:<m>]     control callout failure
     callout_no_where           do not show position of a callout
     callout_none               do not supply a callout function
     copy=<number or name>      copy captured substring
     depth_limit=<n>            set a depth limit
     dfa                        use pcre2_dfa_match()
     find_limits                find heap, match and depth limits
     find_limits_noheap         find match and depth limits
     get=<number or name>       extract captured substring
     getall                     extract all captured substrings
 /g  global                     global matching
     heapframes_size            show match data heapframes size
     heap_limit=<n>             set a limit on heap memory (Kbytes)
     jitstack=<n>               set size of JIT stack
     mark                       show mark values
     match_limit=<n>            set a match limit
     memory                     show heap memory usage
     null_context               match with a NULL context
     null_replacement           substitute with NULL replacement
     null_subject               match with NULL subject
     offset=<n>                 set starting offset
     offset_limit=<n>           set offset limit
     ovector=<n>                set size of output vector
     recursion_limit=<n>        obsolete synonym for depth_limit
     replace=<string>           specify a replacement string
     startchar                  show startchar when relevant
     startoffset=<n>            same as offset=<n>
     substitute_callout         use substitution callouts
     substitute_extedded        use PCRE2_SUBSTITUTE_EXTENDED
     substitute_literal         use PCRE2_SUBSTITUTE_LITERAL
     substitute_matched         use PCRE2_SUBSTITUTE_MATCHED
     substitute_overflow_length use PCRE2_SUBSTITUTE_OVERFLOW_LENGTH
     substitute_replacement_only use PCRE2_SUBSTITUTE_REPLACEMENT_ONLY
     substitute_skip=<n>        skip substitution number n
     substitute_stop=<n>        skip substitution number n and greater
     substitute_unknown_unset   use PCRE2_SUBSTITUTE_UNKNOWN_UNSET
     substitute_unset_empty     use PCRE2_SUBSTITUTE_UNSET_EMPTY
     zero_terminate             pass the subject as zero-terminated

The effects of these modifiers are described in the following sections. When matching via the POSIX wrapper API, the aftertext, allaftertext, and ovector subject modifiers work as described below. All other modifiers are either ignored, with a warning message, or cause an error.

Showing more text

The aftertext modifier requests that as well as outputting the part of the subject string that matched the entire pattern, pcre2test should in addition output the remainder of the subject string. This is useful for tests where the subject contains multiple copies of the same substring. The allaftertext modifier requests the same action for captured substrings as well as the main matched substring. In each case the remainder is output on the following line with a plus character following the capture number.

The allusedtext modifier requests that all the text that was consulted during a successful pattern match by the interpreter should be shown, for both full and partial matches. This feature is not supported for JIT matching, and if requested with JIT it is ignored (with a warning message). Setting this modifier affects the output if there is a lookbehind at the start of a match, or, for a complete match, a lookahead at the end, or if \K is used in the pattern. Characters that precede or follow the start and end of the actual match are indicated in the output by '<' or '>' characters underneath them. Here is an example:

   re> /(?<=pqr)abc(?=xyz)/
 data> 123pqrabcxyz456\=allusedtext
  0: pqrabcxyz
     <<<   >>>
 data> 123pqrabcxy\=ph,allusedtext
 Partial match: pqrabcxy

The first, complete match shows that the matched string is "abc", with the preceding and following strings "pqr" and "xyz" having been consulted during the match (when processing the assertions). The partial match can indicate only the preceding string.

The startchar modifier requests that the starting character for the match be indicated, if it is different to the start of the matched string. The only time when this occurs is when \K has been processed as part of the match. In this situation, the output for the matched string is displayed from the starting character instead of from the match point, with circumflex characters under the earlier characters. For example:

   re> /abc\Kxyz/
 data> abcxyz\=startchar
  0: abcxyz

Unlike allusedtext, the startchar modifier can be used with JIT. However, these two modifiers are mutually exclusive.

Showing the value of all capture groups

The allcaptures modifier requests that the values of all potential captured parentheses be output after a match. By default, only those up to the highest one actually used in the match are output (corresponding to the return code from pcre2_match()). Groups that did not take part in the match are output as "<unset>". This modifier is not relevant for DFA matching (which does no capturing) and does not apply when replace is specified; it is ignored, with a warning message, if present.

Showing the entire ovector, for all outcomes

The allvector modifier requests that the entire ovector be shown, whatever the outcome of the match. Compare allcaptures, which shows only up to the maximum number of capture groups for the pattern, and then only for a successful complete non-DFA match. This modifier, which acts after any match result, and also for DFA matching, provides a means of checking that there are no unexpected modifications to ovector fields. Before each match attempt, the ovector is filled with a special value, and if this is found in both elements of a capturing pair, "<unchanged>" is output. After a successful match, this applies to all groups after the maximum capture group for the pattern. In other cases it applies to the entire ovector. After a partial match, the first two elements are the only ones that should be set. After a DFA match, the amount of ovector that is used depends on the number of matches that were found.

Testing pattern callouts

A callout function is supplied when pcre2test calls the library matching functions, unless callout_none is specified. Its behaviour can be controlled by various modifiers listed above whose names begin with callout_. Details are given in the section entitled "Callouts" below. Testing callouts from pcre2_substitute() is described separately in "Testing the substitution function" below.

Finding all matches in a string

Searching for all possible matches within a subject can be requested by the global or altglobal modifier. After finding a match, the matching function is called again to search the remainder of the subject. The difference between global and altglobal is that the former uses the start_offset argument to pcre2_match() or pcre2_dfa_match() to start searching at a new point within the entire string (which is what Perl does), whereas the latter passes over a shortened subject. This makes a difference to the matching process if the pattern begins with a lookbehind assertion (including \b or \B).

If an empty string is matched, the next match is done with the PCRE2_NOTEMPTY_ATSTART and PCRE2_ANCHORED flags set, in order to search for another, non-empty, match at the same point in the subject. If this match fails, the start offset is advanced, and the normal match is retried. This imitates the way Perl handles such cases when using the /g modifier or the split() function. Normally, the start offset is advanced by one character, but if the newline convention recognizes CRLF as a newline, and the current character is CR followed by LF, an advance of two characters occurs.

Testing substring extraction functions

The copy and get modifiers can be used to test the pcre2_substring_copy_xxx() and pcre2_substring_get_xxx() functions. They can be given more than once, and each can specify a capture group name or number, for example:


If the #subject command is used to set default copy and/or get lists, these can be unset by specifying a negative number to cancel all numbered groups and an empty name to cancel all named groups.

The getall modifier tests pcre2_substring_list_get(), which extracts all captured substrings.

If the subject line is successfully matched, the substrings extracted by the convenience functions are output with C, G, or L after the string number instead of a colon. This is in addition to the normal full list. The string length (that is, the return from the extraction function) is given in parentheses after each substring, followed by the name when the extraction was by name.

Testing the substitution function

If the replace modifier is set, the pcre2_substitute() function is called instead of one of the matching functions (or after one call of pcre2_match() in the case of PCRE2_SUBSTITUTE_MATCHED). Note that replacement strings cannot contain commas, because a comma signifies the end of a modifier. This is not thought to be an issue in a test program.

Specifying a completely empty replacement string disables this modifier. However, it is possible to specify an empty replacement by providing a buffer length, as described below, for an otherwise empty replacement.

Unlike subject strings, pcre2test does not process replacement strings for escape sequences. In UTF mode, a replacement string is checked to see if it is a valid UTF-8 string. If so, it is correctly converted to a UTF string of the appropriate code unit width. If it is not a valid UTF-8 string, the individual code units are copied directly. This provides a means of passing an invalid UTF-8 string for testing purposes.

The following modifiers set options (in additional to the normal match options) for pcre2_substitute():

 global                      PCRE2_SUBSTITUTE_GLOBAL
 substitute_extended         PCRE2_SUBSTITUTE_EXTENDED
 substitute_literal          PCRE2_SUBSTITUTE_LITERAL
 substitute_matched          PCRE2_SUBSTITUTE_MATCHED
 substitute_overflow_length  PCRE2_SUBSTITUTE_OVERFLOW_LENGTH
 substitute_replacement_only PCRE2_SUBSTITUTE_REPLACEMENT_ONLY
 substitute_unknown_unset    PCRE2_SUBSTITUTE_UNKNOWN_UNSET
 substitute_unset_empty      PCRE2_SUBSTITUTE_UNSET_EMPTY

See the pcre2api documentation for details of these options.

After a successful substitution, the modified string is output, preceded by the number of replacements. This may be zero if there were no matches. Here is a simple example of a substitution test:

  1: =xxx=abc=
  2: =xxx=xxx=

Subject and replacement strings should be kept relatively short (fewer than 256 characters) for substitution tests, as fixed-size buffers are used. To make it easy to test for buffer overflow, if the replacement string starts with a number in square brackets, that number is passed to pcre2_substitute() as the size of the output buffer, with the replacement string starting at the next character. Here is an example that tests the edge case:

  1: 123XYZ123
 Failed: error -47: no more memory

The default action of pcre2_substitute() is to return PCRE2_ERROR_NOMEMORY when the output buffer is too small. However, if the PCRE2_SUBSTITUTE_OVERFLOW_LENGTH option is set (by using the substitute_overflow_length modifier), pcre2_substitute() continues to go through the motions of matching and substituting (but not doing any callouts), in order to compute the size of buffer that is required. When this happens, pcre2test shows the required buffer length (which includes space for the trailing zero) as part of the error message. For example:

 Failed: error -47: no more memory: 10 code units are needed

A replacement string is ignored with POSIX and DFA matching. Specifying partial matching provokes an error return ("bad option value") from pcre2_substitute().

Testing substitute callouts

If the substitute_callout modifier is set, a substitution callout function is set up. The null_context modifier must not be set, because the address of the callout function is passed in a match context. When the callout function is called (after each substitution), details of the input and output strings are output. For example:

  1(1) Old 0 3 "abc" New 0 5 "<abc>"
  2(1) Old 6 9 "abc" New 8 13 "<abc>"
  2: <abc>def<abc>pqr

The first number on each callout line is the count of matches. The parenthesized number is the number of pairs that are set in the ovector (that is, one more than the number of capturing groups that were set). Then are listed the offsets of the old substring, its contents, and the same for the replacement.

By default, the substitution callout function returns zero, which accepts the replacement and causes matching to continue if /g was used. Two further modifiers can be used to test other return values. If substitute_skip is set to a value greater than zero the callout function returns +1 for the match of that number, and similarly substitute_stop returns -1. These cause the replacement to be rejected, and -1 causes no further matching to take place. If either of them are set, substitute_callout is assumed. For example:

  1(1) Old 0 3 "abc" New 0 5 "<abc> SKIPPED"
  2(1) Old 6 9 "abc" New 6 11 "<abc>"
  2: abcdef<abc>pqr
  1(1) Old 0 3 "abc" New 0 5 "<abc> STOPPED"
  1: abcdefabcpqr

If both are set for the same number, stop takes precedence. Only a single skip or stop is supported, which is sufficient for testing that the feature works.

Setting the JIT stack size

The jitstack modifier provides a way of setting the maximum stack size that is used by the just-in-time optimization code. It is ignored if JIT optimization is not being used. The value is a number of kibibytes (units of 1024 bytes). Setting zero reverts to the default of 32KiB. Providing a stack that is larger than the default is necessary only for very complicated patterns. If jitstack is set non-zero on a subject line it overrides any value that was set on the pattern.

Setting heap, match, and depth limits

The heap_limit, match_limit, and depth_limit modifiers set the appropriate limits in the match context. These values are ignored when the find_limits or find_limits_noheap modifier is specified.

Finding minimum limits

If the find_limits modifier is present on a subject line, pcre2test calls the relevant matching function several times, setting different values in the match context via pcre2_set_heap_limit(), pcre2_set_match_limit(), or pcre2_set_depth_limit() until it finds the smallest value for each parameter that allows the match to complete without a "limit exceeded" error. The match itself may succeed or fail. An alternative modifier, find_limits_noheap, omits the heap limit. This is used in the standard tests, because the minimum heap limit varies between systems. If JIT is being used, only the match limit is relevant, and the other two are automatically omitted.

When using this modifier, the pattern should not contain any limit settings such as (*LIMIT_MATCH=...) within it. If such a setting is present and is lower than the minimum matching value, the minimum value cannot be found because pcre2_set_match_limit() etc. are only able to reduce the value of an in-pattern limit; they cannot increase it.

For non-DFA matching, the minimum depth_limit number is a measure of how much nested backtracking happens (that is, how deeply the pattern's tree is searched). In the case of DFA matching, depth_limit controls the depth of recursive calls of the internal function that is used for handling pattern recursion, lookaround assertions, and atomic groups.

For non-DFA matching, the match_limit number is a measure of the amount of backtracking that takes place, and learning the minimum value can be instructive. For most simple matches, the number is quite small, but for patterns with very large numbers of matching possibilities, it can become large very quickly with increasing length of subject string. In the case of DFA matching, match_limit controls the total number of calls, both recursive and non-recursive, to the internal matching function, thus controlling the overall amount of computing resource that is used.

For both kinds of matching, the heap_limit number, which is in kibibytes (units of 1024 bytes), limits the amount of heap memory used for matching.

Showing MARK names

The mark modifier causes the names from backtracking control verbs that are returned from calls to pcre2_match() to be displayed. If a mark is returned for a match, non-match, or partial match, pcre2test shows it. For a match, it is on a line by itself, tagged with "MK:". Otherwise, it is added to the non-match message.

Showing memory usage

The memory modifier causes pcre2test to log the sizes of all heap memory allocation and freeing calls that occur during a call to pcre2_match() or pcre2_dfa_match(). In the latter case, heap memory is used only when a match requires more internal workspace that the default allocation on the stack, so in many cases there will be no output. No heap memory is allocated during matching with JIT. For this modifier to work, the null_context modifier must not be set on both the pattern and the subject, though it can be set on one or the other.

Showing the heap frame overall vector size

The heapframes_size modifier is relevant for matches using pcre2_match() without JIT. After a match has run (whether successful or not) the size, in bytes, of the allocated heap frames vector that is left attached to the match data block is shown. If the matching action involved several calls to pcre2_match() (for example, global matching or for timing) only the final value is shown.

This modifier is ignored, with a warning, for POSIX or DFA matching. JIT matching does not use the heap frames vector, so the size is always zero, unless there was a previous non-JIT match. Note that specifing a size of zero for the output vector (see below) causes pcre2test to free its match data block (and associated heap frames vector) and allocate a new one.

Setting a starting offset

The offset modifier sets an offset in the subject string at which matching starts. Its value is a number of code units, not characters.

Setting an offset limit

The offset_limit modifier sets a limit for unanchored matches. If a match cannot be found starting at or before this offset in the subject, a "no match" return is given. The data value is a number of code units, not characters. When this modifier is used, the use_offset_limit modifier must have been set for the pattern; if not, an error is generated.

Setting the size of the output vector

The ovector modifier applies only to the subject line in which it appears, though of course it can also be used to set a default in a #subject command. It specifies the number of pairs of offsets that are available for storing matching information. The default is 15.

A value of zero is useful when testing the POSIX API because it causes regexec() to be called with a NULL capture vector. When not testing the POSIX API, a value of zero is used to cause pcre2_match_data_create_from_pattern() to be called, in order to create a new match block of exactly the right size for the pattern. (It is not possible to create a match block with a zero-length ovector; there is always at least one pair of offsets.) The old match data block is freed.

Passing the subject as zero-terminated

By default, the subject string is passed to a native API matching function with its correct length. In order to test the facility for passing a zero-terminated string, the zero_terminate modifier is provided. It causes the length to be passed as PCRE2_ZERO_TERMINATED. When matching via the POSIX interface, this modifier is ignored, with a warning.

When testing pcre2_substitute(), this modifier also has the effect of passing the replacement string as zero-terminated.

Passing a NULL context, subject, or replacement

Normally, pcre2test passes a context block to pcre2_match(), pcre2_dfa_match(), pcre2_jit_match() or pcre2_substitute(). If the null_context modifier is set, however, NULL is passed. This is for testing that the matching and substitution functions behave correctly in this case (they use default values). This modifier cannot be used with the find_limits, find_limits_noheap, or substitute_callout modifiers.

Similarly, for testing purposes, if the null_subject or null_replacement modifier is set, the subject or replacement string pointers are passed as NULL, respectively, to the relevant functions.

The Alternative Matching Function

By default, pcre2test uses the standard PCRE2 matching function, pcre2_match() to match each subject line. PCRE2 also supports an alternative matching function, pcre2_dfa_match(), which operates in a different way, and has some restrictions. The differences between the two functions are described in the pcre2matching documentation.

If the dfa modifier is set, the alternative matching function is used. This function finds all possible matches at a given point in the subject. If, however, the dfa_shortest modifier is set, processing stops after the first match is found. This is always the shortest possible match.


This section describes the output when the normal matching function, pcre2_match(), is being used.

When a match succeeds, pcre2test outputs the list of captured substrings, starting with number 0 for the string that matched the whole pattern. Otherwise, it outputs "No match" when the return is PCRE2_ERROR_NOMATCH, or "Partial match:" followed by the partially matching substring when the return is PCRE2_ERROR_PARTIAL. (Note that this is the entire substring that was inspected during the partial match; it may include characters before the actual match start if a lookbehind assertion, \K, \b, or \B was involved.)

For any other return, pcre2test outputs the PCRE2 negative error number and a short descriptive phrase. If the error is a failed UTF string check, the code unit offset of the start of the failing character is also output. Here is an example of an interactive pcre2test run.

 $ pcre2test
 PCRE2 version 10.22 2016-07-29

   re> /^abc(\d+)/
 data> abc123
  0: abc123
  1: 123
 data> xyz
 No match

Unset capturing substrings that are not followed by one that is set are not shown by pcre2test unless the allcaptures modifier is specified. In the following example, there are two capturing substrings, but when the first data line is matched, the second, unset substring is not shown. An "internal" unset substring is shown as "<unset>", as for the second data line.

   re> /(a)|(b)/
 data> a
  0: a
  1: a
 data> b
  0: b
  1: <unset>
  2: b

If the strings contain any non-printing characters, they are output as \xhh escapes if the value is less than 256 and UTF mode is not set. Otherwise they are output as \x{hh...} escapes. See below for the definition of non-printing characters. If the aftertext modifier is set, the output for substring 0 is followed by the rest of the subject string, identified by "0+" like this:

   re> /cat/aftertext
 data> cataract
  0: cat
  0+ aract

If global matching is requested, the results of successive matching attempts are output in sequence, like this:

   re> /\Bi(\w\w)/g
 data> Mississippi
  0: iss
  1: ss
  0: iss
  1: ss
  0: ipp
  1: pp

"No match" is output only if the first match attempt fails. Here is an example of a failure message (the offset 4 that is specified by the offset modifier is past the end of the subject string):

   re> /xyz/
 data> xyz\=offset=4
 Error -24 (bad offset value)

Note that whereas patterns can be continued over several lines (a plain ">" prompt is used for continuations), subject lines may not. However newlines can be included in a subject by means of the \n escape (or \r, \r\n, etc., depending on the newline sequence setting).

Output from the Alternative Matching Function

When the alternative matching function, pcre2_dfa_match(), is used, the output consists of a list of all the matches that start at the first point in the subject where there is at least one match. For example:

   re> /(tang|tangerine|tan)/
 data> yellow tangerine\=dfa
  0: tangerine
  1: tang
  2: tan

Using the normal matching function on this data finds only "tang". The longest matching string is always given first (and numbered zero). After a PCRE2_ERROR_PARTIAL return, the output is "Partial match:", followed by the partially matching substring. Note that this is the entire substring that was inspected during the partial match; it may include characters before the actual match start if a lookbehind assertion, \b, or \B was involved. (\K is not supported for DFA matching.)

If global matching is requested, the search for further matches resumes at the end of the longest match. For example:

   re> /(tang|tangerine|tan)/g
 data> yellow tangerine and tangy sultana\=dfa
  0: tangerine
  1: tang
  2: tan
  0: tang
  1: tan
  0: tan

The alternative matching function does not support substring capture, so the modifiers that are concerned with captured substrings are not relevant.

Restarting After a Partial Match

When the alternative matching function has given the PCRE2_ERROR_PARTIAL return, indicating that the subject partially matched the pattern, you can restart the match with additional subject data by means of the dfa_restart modifier. For example:

   re> /^\d?\d(jan|feb|mar|apr|may|jun|jul|aug|sep|oct|nov|dec)\d\d$/
 data> 23ja\=ps,dfa
 Partial match: 23ja
 data> n05\=dfa,dfa_restart
  0: n05

For further information about partial matching, see the pcre2partial documentation.


If the pattern contains any callout requests, pcre2test's callout function is called during matching unless callout_none is specified. This works with both matching functions, and with JIT, though there are some differences in behaviour. The output for callouts with numerical arguments and those with string arguments is slightly different.

Callouts with numerical arguments

By default, the callout function displays the callout number, the start and current positions in the subject text at the callout time, and the next pattern item to be tested. For example:

   0    ^  ^     \d

This output indicates that callout number 0 occurred for a match attempt starting at the fourth character of the subject string, when the pointer was at the seventh character, and when the next pattern item was \d. Just one circumflex is output if the start and current positions are the same, or if the current position precedes the start position, which can happen if the callout is in a lookbehind assertion.

Callouts numbered 255 are assumed to be automatic callouts, inserted as a result of the auto_callout pattern modifier. In this case, instead of showing the callout number, the offset in the pattern, preceded by a plus, is output. For example:

   re> /\d?[A-E]\*/auto_callout
 data> E*
  +0 ^      \d?
  +3 ^      [A-E]
  +8 ^^     \*
 +10 ^ ^
  0: E*

If a pattern contains (*MARK) items, an additional line is output whenever a change of latest mark is passed to the callout function. For example:

   re> /a(*MARK:X)bc/auto_callout
 data> abc
  +0 ^       a
  +1 ^^      (*MARK:X)
 +10 ^^      b
 Latest Mark: X
 +11 ^ ^     c
 +12 ^  ^
  0: abc

The mark changes between matching "a" and "b", but stays the same for the rest of the match, so nothing more is output. If, as a result of backtracking, the mark reverts to being unset, the text "<unset>" is output.

Callouts with string arguments

The output for a callout with a string argument is similar, except that instead of outputting a callout number before the position indicators, the callout string and its offset in the pattern string are output before the reflection of the subject string, and the subject string is reflected for each callout. For example:

   re> /^ab(?C'first')cd(?C"second")ef/
 data> abcdefg
 Callout (7): 'first'
     ^ ^         c
 Callout (20): "second"
     ^   ^       e
  0: abcdef

Callout modifiers

The callout function in pcre2test returns zero (carry on matching) by default, but you can use a callout_fail modifier in a subject line to change this and other parameters of the callout (see below).

If the callout_capture modifier is set, the current captured groups are output when a callout occurs. This is useful only for non-DFA matching, as pcre2_dfa_match() does not support capturing, so no captures are ever shown.

The normal callout output, showing the callout number or pattern offset (as described above) is suppressed if the callout_no_where modifier is set.

When using the interpretive matching function pcre2_match() without JIT, setting the callout_extra modifier causes additional output from pcre2test's callout function to be generated. For the first callout in a match attempt at a new starting position in the subject, "New match attempt" is output. If there has been a backtrack since the last callout (or start of matching if this is the first callout), "Backtrack" is output, followed by "No other matching paths" if the backtrack ended the previous match attempt. For example:

  re> /(a+)b/auto_callout,no_start_optimize,no_auto_possess
 data> aac\=callout_extra
 New match attempt
  +0 ^       (
  +1 ^       a+
  +3 ^ ^     )
  +4 ^ ^     b
  +3 ^^      )
  +4 ^^      b
 No other matching paths
 New match attempt
  +0  ^      (
  +1  ^      a+
  +3  ^^     )
  +4  ^^     b
 No other matching paths
 New match attempt
  +0   ^     (
  +1   ^     a+
 No other matching paths
 New match attempt
  +0    ^    (
  +1    ^    a+
 No match

Notice that various optimizations must be turned off if you want all possible matching paths to be scanned. If no_start_optimize is not used, there is an immediate "no match", without any callouts, because the starting optimization fails to find "b" in the subject, which it knows must be present for any match. If no_auto_possess is not used, the "a+" item is turned into "a++", which reduces the number of backtracks.

The callout_extra modifier has no effect if used with the DFA matching function, or with JIT.

Return values from callouts

The default return from the callout function is zero, which allows matching to continue. The callout_fail modifier can be given one or two numbers. If there is only one number, 1 is returned instead of 0 (causing matching to backtrack) when a callout of that number is reached. If two numbers (<n>:<m>) are given, 1 is returned when callout <n> is reached and there have been at least <m> callouts. The callout_error modifier is similar, except that PCRE2_ERROR_CALLOUT is returned, causing the entire matching process to be aborted. If both these modifiers are set for the same callout number, callout_error takes precedence. Note that callouts with string arguments are always given the number zero.

The callout_data modifier can be given an unsigned or a negative number. This is set as the "user data" that is passed to the matching function, and passed back when the callout function is invoked. Any value other than zero is used as a return from pcre2test's callout function.

Inserting callouts can be helpful when using pcre2test to check complicated regular expressions. For further information about callouts, see the pcre2callout documentation.

Non-Printing Characters

When pcre2test is outputting text in the compiled version of a pattern, bytes other than 32-126 are always treated as non-printing characters and are therefore shown as hex escapes.

When pcre2test is outputting text that is a matched part of a subject string, it behaves in the same way, unless a different locale has been set for the pattern (using the locale modifier). In this case, the isprint() function is used to distinguish printing and non-printing characters.

Saving and Restoring Compiled Patterns

It is possible to save compiled patterns on disc or elsewhere, and reload them later, subject to a number of restrictions. JIT data cannot be saved. The host on which the patterns are reloaded must be running the same version of PCRE2, with the same code unit width, and must also have the same endianness, pointer width and PCRE2_SIZE type. Before compiled patterns can be saved they must be serialized, that is, converted to a stream of bytes. A single byte stream may contain any number of compiled patterns, but they must all use the same character tables. A single copy of the tables is included in the byte stream (its size is 1088 bytes).

The functions whose names begin with pcre2_serialize_ are used for serializing and de-serializing. They are described in the pcre2serialize documentation. In this section we describe the features of pcre2test that can be used to test these functions.

Note that "serialization" in PCRE2 does not convert compiled patterns to an abstract format like Java or .NET. It just makes a reloadable byte code stream. Hence the restrictions on reloading mentioned above.

In pcre2test, when a pattern with push modifier is successfully compiled, it is pushed onto a stack of compiled patterns, and pcre2test expects the next line to contain a new pattern (or command) instead of a subject line. By contrast, the pushcopy modifier causes a copy of the compiled pattern to be stacked, leaving the original available for immediate matching. By using push and/or pushcopy, a number of patterns can be compiled and retained. These modifiers are incompatible with posix, and control modifiers that act at match time are ignored (with a message) for the stacked patterns. The jitverify modifier applies only at compile time.

The command

 #save <filename>

causes all the stacked patterns to be serialized and the result written to the named file. Afterwards, all the stacked patterns are freed. The command

 #load <filename>

reads the data in the file, and then arranges for it to be de-serialized, with the resulting compiled patterns added to the pattern stack. The pattern on the top of the stack can be retrieved by the #pop command, which must be followed by lines of subjects that are to be matched with the pattern, terminated as usual by an empty line or end of file. This command may be followed by a modifier list containing only control modifiers that act after a pattern has been compiled. In particular, hex, posix, posix_nosub, push, and pushcopy are not allowed, nor are any option-setting modifiers. The JIT modifiers are, however permitted. Here is an example that saves and reloads two patterns.

 #save tempfile
 #load tempfile
 #pop info

 #pop jit,bincode

If jitverify is used with #pop, it does not automatically imply jit, which is different behaviour from when it is used on a pattern.

The #popcopy command is analogous to the pushcopy modifier in that it makes current a copy of the topmost stack pattern, leaving the original still on the stack.

See Also

pcre2(3), pcre2api(3), pcre2callout(3), pcre2jit, pcre2matching(3), pcre2partial(d), pcre2pattern(3), pcre2serialize(3).


Philip Hazel
Retired from University Computing Service
Cambridge, England.


Last updated: 24 April 2024
Copyright (c) 1997-2024 University of Cambridge.


24 April 2024 PCRE 10.44