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swatch - Man Page

simple watcher


swatch  [ --awk-field-syntax ] [ --config-file|-c file ]  [ --daemon ]  [ --extra-include-dir|-I path ] [ --extra-module|-M module_name ] [ --help|-h ] [ --input-record-separator regex ]  [ --old-style-config|-O ] [ --pid-file file ] [ --restart-time|-r time ]  [ --script-dir path ] [ --tail-args arguments_for_tail_program ] [ --tail-program-name filename ] [ --version|-V ] [ --use-cpan-file-tail ] [ [ --examine|-f file_to_examine ]  | [ --read-pipe|-p program_to_pipe_from ]  | [ --tail-file|-t file_to_tail ] ] [ --debug [ level ] ]  [ --dump-script filename ]


Swatch is designed to monitor system activity. In order for Swatch to be useful, it requires a configuration file which contains pattern(s) to look for and action(s) to perform when each pattern is found.

Command Line Options


Use this option only if you want to overide regular expression backreferencing in favor of awk(1) style field referencing. Included for backward  compatibility.

--config-file|-c filename

Tells swatch where to find its configuration file. The default is ${HOME}/.swatchrc.


This tells swatch to run in the background and disassociate itself from  any terminal.

--extra-include-dir|-I path

This tells swatch where to look for custom action modules.

--extra-module|-M module_name

This tells swatch what custom action modules to load in.


Prints usage information and exits.


Tells swatch to use regular_expression to delineate the boundary of each input record. The default is a carriage return.


This tells swatch that your configuration file is written using the syntax that was abandoned back in the 1990's.

--pid-file file

Writes the process ID to file. Useful when running in daemon mode.

--restart-time=[+]hh:mm[am|pm] or -r [+]hh:mm[am|pm]

Restart at the specified time where hh is hours and mm is minutes.  If the am/pm indicator is omitted, then a 24-hour clock is assumed.  If the time is preceded by the "+" character, then the restart time  will be set to the current time plus the specified time and the am/pm indicator will be ignored.


This switch causes the temporary watcher script to be written to a file in the specified directory rather than the user's home directory. It is highly advised that you do NOT use directories that are writable by others such as /tmp.

--tail-args arguments_for_tail_program

Pass specific options to the tail(1) program.

--tail-program-name filename

Runs an alternate tail(1) like program instead of the system default.

--version or -V

Prints version information and exits.


Use CPAN's File::Tail module to read the log file instead of the tail(1)  command.

You may specify only one of the following options:

--tail-file=filename or -t filename

Examine lines of text as they are added to filename.

--read-pipe=command or -p command

Examine input piped in from the command.

--examine=filename or -f filename

Use filename as the file to examine.  Swatch will do a single pass through the named file.

The following options are purely for debugging purposes, but are documented here for completeness:


Spew out various levels of debugging for swatch developers.


Instead of running the watcher script after it is generated,  it is written to filename or to STDOUT.

If swatch is called with no options, it is the same as typing the  command line

        swatch --config-file=~/.swatchrc --tail-file=/var/log/syslog

or if /var/log/messages exists

        swatch --config-file=~/.swatchrc --tail-file=/var/log/messages

The Configuration File

The configuration file is used by the swatch(8) program to determine what types of expression patterns to look for and what type of action(s) should be taken when a pattern is matched.

Each line should contain a keyword and a, sometimes optional, value for that keyword. The keyword and value are separated by  a space or an equal (=) sign.

watchfor regex

ignore regex

echo [modes]

Echo the matched line. The text mode may be normal, bold, underscore, blink, inverse,  black, red, green, yellow, blue, magenta, cyan, white, black_h, red_h, green_h, yellow_h, blue_h,  magenta_h, cyan_h, and/or white_h. The _h colors specify  a highlighting color. The other colors are assigned to the letters. Some modes may not work on some terminals. Normal is the default.

bell [N]

Echo the matched line, and send a bell N times (default = 1).

exec command

Execute command. The command may contain variables which are  substituted with fields from the matched line. If the --awk-field-syntax command-line option has been specified, then each $N will be replaced by the Nth field in the line. If the option has not been specified, then each $N will refer to a backreference in the regular expression used to match the line.

A $0 or $* will always be replaced by the entire line, unless they have been escaped, regardless of the --awk-field-syntax option.

An escaped $N, $0 or $* may have unwanted effects since the value will be determined by the shell used to execute the command.

mail [addresses=address:address:...][,subject=your_text_here]

Send mail to address(es) containing the matched lines as they appear (default address is the user who is running the program).

pipe command[,keep_open]

Pipe matched lines into command. Use the keep_open option to  force the pipe to stay open until a different pipe action is run or  until swatch exits.

write [user:user:...]

Use write(1) to send matched lines to user(s).

throttle hours:minutes:seconds,[key=message|regex|<regexE]>

This action has been depreciated. Use threshold instead For example,

throttle 15:00,key="foo"

would look like this

threshold track_by="foo",type=limit,count=1,seconds=900

threshold track_by=key, type=<limit|threshold|both, count=number, seconds=number>

Thresholding can be done for the complete watchfor block and/or for individual actions. Add "threshold=on" as an option along with the other threshold options when thresholding an individual action.


The value of this should be something that is unique to the watchfor regular expression. Tip: enclose unique parts of the regular expression in parentheses, then use the sub matches as part of the value  (e.g. track_by="$2:$4").


There are three types of thresholding. They are as follows:


Perform action(s) for the first "count" matches during the time interval specified by "seconds", then ignore events for the rest of the time interval (kind of like throttle)


Perform action(s) on each match for up to count matches during the  time interval specified by seconds


Perform actions(s) once per time interval after "count" matches occur, then ignore additional matches during the time interval  specified by "seconds"


Use this action to cause swatch to continue to try to match other pattern/action groups after it is done with the current pattern/action block.


Use this action to cause swatch to clean up and quit immediately.

Special Option

The following may be used as an option for any of the above actions except for throttle and threshold.


Use this option to specify windows of time and days when the action can  be performed.  For example:


For Perl Hacks Only

perlcode [depth] arbitrary_Perl_code

This permits you to easily insert random Perl code into your swatchrc file. The optional depth value tells swatch how deep into the code to put the perl  code. (0=outside the main loop, 1=inside the main loop (default), 2=just inside the  conditional used by the current watchfor statement, and 3=inside the throttle block).

Its intended use is to permit variable substitution. For example:

perlcode $syslog="^\w{3}\s+\d{1,2}\s+\d{2}:\d{2}:\d{2}.*";

watchfor /$syslog hostname pppd/>

but any valid Perl is permitted.  Remember the semicolon, and make judicious use of the --dump-script option if you run into trouble.

Configuration Example

perlcode my $fsf_regex = '\d{2}:\d{2}:\d{2}\s+(.* file system full)';

watchfor /$fsf_regex/
   threshold track_by=$1,type=limit,count=1,seconds=60

In this example, a line which contains the string "file system full" will be echoed and the screen bell will sound.  Also, threshold will use what  is matched within the parentheses as its key rather than trying to use the  log message with its time stamp cut out. Multiple instances of the message will not be echoed if they appear within a minute of the  first one. Instead the following message will be acted upon after  the time interval has expired.

See Also

signal(3), perl(1), perlre(1)


Upon receiving an ALRM or HUP signal swatch will re-read the configuration file and restart, except when used with the --daemon  command line option where it will simply exit. Swatch will terminate gracefully when it receives a QUIT, TERM, or INT signal.


    E. Todd Atkins


Swatch is a SourceForge project whose project page is at  http://sourceforge.net/projects/swatch and homepage is at http://swatch.sourceforge.net


2024-01-27 perl v5.38.2 User Contributed Perl Documentation