Extensions in GNU `m4' ====================== This version of `m4' contains a few facilities, that do not exist in System V `m4'. These extra facilities are all suppressed by using the `-G' command line option, unless overridden by other command line options. * In the `$'N notation for macro arguments, N can contain several digits, while the System V `m4' only accepts one digit. This allows macros in GNU `m4' to take any number of arguments, and not only nine (Note: Arguments). * Files included with `include' and `sinclude' are sought in a user specified search path, if they are not found in the working directory. The search path is specified by the `-I' option and the `M4PATH' environment variable (Note: Search Path). * Arguments to `undivert' can be non-numeric, in which case the named file will be included uninterpreted in the output (Note: Undivert). * Formatted output is supported through the `format' builtin, which is modeled after the C library function `printf' (Note: Format). * Searches and text substitution through regular expressions are supported by the `regexp' (Note: Regexp) and `patsubst' (Note: Patsubst) builtins. * The output of shell commands can be read into `m4' with `esyscmd' (Note: Esyscmd). * There is indirect access to any builtin macro with `builtin' (Note: Builtin). * Macros can be called indirectly through `indir' (Note: Indir). * The name of the current input file and the current input line number are accessible through the builtins `__file__' and `__line__' (Note: Errprint). * The format of the output from `dumpdef' and macro tracing can be controlled with `debugmode' (Note: Debug Levels). * The destination of trace and debug output can be controlled with `debugfile' (Note: Debug Output). In addition to the above extensions, GNU `m4' implements the following command line options: `-F', `-G', `-I', `-L', `-R', `-V', `-W', `-d', `-l', `-o' and `-t'. Note: Invoking m4, for a description of these options. Also, the debugging and tracing facilities in GNU `m4' are much more extensive than in most other versions of `m4'.
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