macro processor
SYNTAX
m4 [Options...] [Macro-Definitions...] [Input-File...]
m4 is a macro processor, in the sense that it copies its input to the output,
expanding macros as it goes. Macros are either builtin or user-defined, and
can take any number of arguments. Besides just doing macro expansion, 'm4' has
builtin functions for including named files, running UNIX commands, doing integer
arithmetic, manipulating text in various ways, recursion, etc... 'm4' can be
used either as a front-end to a compiler, or as a macro processor in its own
right.
The 'm4' macro processor is widely available on all UNIXes. Usually, only a
small percentage of users are aware of its existence.
However, those who do often become commited users.
Some people found 'm4' to be fairly addictive. They first use 'm4' for simple
problems, then take bigger and bigger challenges, learning how to write complex
'm4' sets of macros along the way. Once really addicted, users pursue writing
of sophisticated 'm4' applications even to solve simple problems, devoting more
time debugging their 'm4' scripts than doing real work. Beware that 'm4' can
be dangerous for the health of compulsive programmers.
see info m4 for the full user manual
OPTIONS
--version
Print the version number of the program on standard output, then
immediately exit 'm4' without reading any INPUT-FILES.
--help
Print an help summary on standard output, then immediately exit
'm4' without reading any INPUT-FILES.
-G
--traditional
Suppress all the extensions made in this implementation, compared
to the System V version.
-E
--fatal-warnings
Stop execution and exit 'm4' once the first warning has been
issued, considering all of them to be fatal.
-d FLAGS
--debug=FLAGS
Set the debug-level according to the flags FLAGS. The debug-level
controls the format and amount of information presented by the
debugging functions. *see below for more details on the
format and meaning of FLAGS.
-l NUM
--arglength=NUM
Restrict the size of the output generated by macro tracing.
-o FILE
--error-output=FILE'
Redirect debug and trace output to the named file. Error messages
are still printed on the standard error output. *Note Debug
Output:: for more details.
-I DIR
--include=DIR
Make 'm4' search DIR for included files that are not found in the
current working directory. *Note Search Path:: for more details.
-e
--interactive
Makes this invocation of 'm4' interactive. This means that all
output will be unbuffered, and interrupts will be ignored.
-s
--synclines
Generate synchronisation lines, for use by the C preprocessor or
other similar tools. This is useful, for example, when 'm4' is
used as a front end to a compiler. Source file name and line
number information is conveyed by directives of the form '#line
LINENUM "FILENAME"', which are inserted as needed into the middle
of the input. Such directives mean that the following line
originated or was expanded from the contents of input file
FILENAME at line LINENUM. The '"FILENAME"' part is often omitted
when the file name did not change from the previous directive.
Synchronisation directives are always given on complete lines per
themselves. When a synchronisation discrepancy occurs in the
middle of an output line, the associated synchronisation directive
is delayed until the beginning of the next generated line.
-P
--prefix-builtins
Internally modify *all* builtin macro names so they all start with
the prefix 'm4_'. For example, using this option, one should write
'm4_define' instead of 'define', and 'm4___file__' instead of
'__file__'.
-W REGEXP
--word-regexp=REGEXP
Use an alternative syntax for macro names. This experimental
option might not be present on all GNU 'm4' implementations.
(*note Changeword::.).
-H N
--hashsize=N
Make the internal hash table for symbol lookup be N entries big.
The number should be prime. The default is 509 entries. It
should not be necessary to increase this value, unless you define
an excessive number of macros.
-L N
--nesting-limit=N
Artificially limit the nesting of macro calls to N levels,
stopping program execution if this limit is ever exceeded. When
not specified, nesting is limited to 250 levels.
The precise effect of this option might be more correctly
associated with textual nesting than dynamic recursion. It has
been useful when some complex 'm4' input was generated by
mechanical means. Most users would never need this option. If
shown to be obtrusive, this option (which is still experimental)
might well disappear.
This option does *not* have the ability to break endless
rescanning loops, while these do not necessarily consume much
memory or stack space. Through clever usage of rescanning loops,
one can request complex, time-consuming computations to 'm4' with
useful results. Putting limitations in this area would break 'm4'
power. There are many pathological cases: 'define('a', 'a')a' is
only the simplest example (but *note Compatibility::.). Expecting
GNU 'm4' to detect these would be a little like expecting a
compiler system to detect and diagnose endless loops: it is a
quite *hard* problem in general, if not undecidable!
-Q
--quiet
--silent
Suppress warnings about missing or superflous arguments in macro
calls.
-B
-S
-T
These options are present for compatibility with System V 'm4', but
do nothing in this implementation.
-N N
--diversions=N
These options are present only for compatibility with previous
versions of GNU 'm4', and were controlling the number of possible
diversions which could be used at the same time. They do nothing,
because there is no fixed limit anymore.
Macro definitions and deletions can be made on the command line, by
using the '-D' and '-U' options. They have the following format:
-D NAME
-D NAME=VALUE
--define=NAME
--define=NAME=VALUE
This enters NAME into the symbol table, before any input files are
read. If '=VALUE' is missing, the value is taken to be the empty
string. The VALUE can be any string, and the macro can be defined
to take arguments, just as if it was defined from within the input.
-U NAME
--undefine=NAME
This deletes any predefined meaning NAME might have. Obviously,
only predefined macros can be deleted in this way.
-t NAME
--trace=NAME
This enters NAME into the symbol table, as undefined but traced.
The macro will consequently be traced from the point it is defined.
-F FILE
--freeze-state FILE
Once execution is finished, write out the frozen state on the
specified FILE (*note Frozen files::.).
-R FILE
--reload-state FILE
Before execution starts, recover the internal state from the
specified frozen FILE (*note Frozen files::.).
FLAGS is any of:
a show actual arguments
c show before collect, after collect and after call
e show expansion
f say current input file name
i show changes in input files
l say current input line number
p show results of path searches
q quote values as necessary, with a or e flag
t trace for all macro calls, not only traceon'ed
x add a unique macro call id, useful with
c flag
V shorthand for all of the above flags
The remaining arguments on the command line are taken to be input
file names. If no names are present, the standard input is read. A
file name of '-' is taken to mean the standard input.
The input files are read in the sequence given. The standard input
can only be read once, so the filename '-' should only appear once on
the command line.
If defined, the environment variable 'M4PATH' is a colon-separated list of directories included after any specified by '-I'.
Exit status is 0 for success, 1 for failure, 63 for frozen file version mismatch, or whatever value was passed to the m4exit macro.
"To try to understand the workings of the economy by means of macroeconomics is rather like trying to understand how a clock works by observing the movements of the hands on its face" ~ David Simpson
Related linux commands:
awk - Find and Replace text within file(s).
expr - Evaluate expressions.
eval - Evaluate several commands/arguments.
for - Expand words, and execute commands.
grep - search file(s) for lines that match a given pattern.
Equivalent Windows commands: DOSKEY - Edit command line, recall commands,
and create macros.