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g.message.1grass - Man Page


g.message — Prints a message, warning, progress info, or fatal error in the GRASS way.
This module should be used in scripts for messages served to user.


general, support, scripts


g.message --help
g.message [-wedpiv] message=string  [debug=integer]   [--help]  [--verbose]  [--quiet]  [--ui]



Print message as warning


Print message as fatal error


Print message as debug message


Print message as progress info


Print message in all modes except of quiet mode
Message is printed on GRASS_VERBOSE>=1


Print message only in verbose mode
Message is printed only on GRASS_VERBOSE>=3


Print usage summary


Verbose module output


Quiet module output


Force launching GUI dialog


message=string [required]

Text of the message to be printed
Message is printed on GRASS_VERBOSE>=2


Level to use for debug messages
Options: 0-5
Default: 1


This program is to be used in Shell/Perl/Python scripts, so the author does not need to use the echo program. The advantage of g.message is that it formats messages just like other GRASS modules do and that its functionality is influenced by the GRASS_VERBOSE and GRASS_MESSAGE_FORMAT environment variables.

The program can be used for standard informative messages as well as warnings (-w flag) and fatal errors (-e flag). For debugging purposes, the -d flag will cause g.message to print a debugging message at the given level.


Messages containing "=" must use the full message= syntax so the parser doesn’t get confused.

If you want a long message (multi-line) to be dealt with as a single paragraph, use a single call to g.message with text split in the script using the backslash as the last character. (In shell scripts don’t close the "quote")

A blank line may be obtained with

g.message message=""

Redundant whitespace will be stripped away.

It’s advisable to single quote the messages that are to be printed literally. It prevents a number of characters (most notably, space and the dollar sign ’$’) from being treated specifically by the shell.

When it is necessary to include, for example, a variable’s value as part of the message, the double quotes may be used, which do not deprive the dollar sign of its special variable-expansion powers.

While it is known that the interactive Bash instances may treat the exclamation mark ’!’ character specifically (making single quoting of it necessary), it shouldn’t be the case for the non-interactive instances of Bash. Nonetheless, to avoid context-based confusion later on you are encouraged to single-quote messages that do not require $VARIABLE expansion.

Usage in Python scripts

GRASS Python Scripting Library defines special wrappers for g.message.
  • debug() for g.message -d
  • error() for g.message -e
  • fatal() for g.message -e + exit()
  • info() for g.message -i
  • message() for g.message
  • verbose() for g.message -v
  • warning() for g.message -w

Note: The Python tab in the wxGUI can be used for entering the following sample code:

import grass.script as gcore
gcore.warning("This is a warning")

is identical with

g.message -w message="This is a warning"

Verbosity Levels

Controlled by the "GRASS_VERBOSE" environment variable. Typically this is set using the --quiet or --verbose command line options.

  • 0 - only errors and warnings are printed
  • 1 - progress messages are printed
  • 2 - all module messages are printed
  • 3 - additional verbose messages are printed

Debug Levels

Controlled by the "DEBUG" GRASS gisenv variable (set with g.gisenv).
Recommended levels:

  • 1 - message is printed once or few times per module
  • 3 - each row (raster) or line (vector)
  • 5 - each cell (raster) or point (vector)


This basic example prints the message "hello" in the console:

g.message message="hello"

To print a message as an error message use the -e flag:

g.message -e message="my error"

To print a message highlighted as a debug message ("D0/0: debug") in the console, use the -d flag. Optionally the debug level can be defined (see also g.gisenv for details):

# Levels: (recommended levels)
#   0 - silence
#   1 - message is printed once or few times per module
#   3 - each row (raster) or line (vector)
#   5 - each cell (raster) or point (vector)
g.message -d message="debug" debug=0

To print a message highlighted as a warning message ("WARNING: my warning") in the console, use the -w flag:

g.message -w message="my warning"

See Also

GRASS variables and environment variables
g.gisenv, g.parser


Jachym Cepicky

Source Code

Available at: g.message source code (history)

Accessed: Tuesday May 14 13:39:58 2024

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