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.
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 ""
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. None the less, to avoid context-based confusion later on you are enouraged to single-quote messages that do not require $VARIABLE expansion.
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