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8.4 Programming in M4sh
M4sh, pronounced “mash”, is aiming at producing portable Bourne shell
scripts. This name was coined by Lars J. Aas, who notes that,
according to the Webster's Revised Unabridged Dictionary (1913):
Mash \Mash\, n. [Akin to G. meisch, maisch, meische, maische, mash,
wash, and prob. to AS. miscian to mix. See “Mix”.]
- A mass of mixed ingredients reduced to a soft pulpy state by beating or
pressure...
- A mixture of meal or bran and water fed to animals.
- A mess; trouble. [Obs.] –Beau. & Fl.
For the time being, it is not mature enough to be widely used.
M4sh provides portable alternatives for some common shell constructs
that unfortunately are not portable in practice.
— Macro: AS_BOURNE_COMPATIBLE
Set up the shell to be more compatible with the Bourne shell as
standardized by Posix, if possible. This may involve setting
environment variables, or setting options, or similar
implementation-specific actions.
— Macro: AS_CASE ( word, [pattern1], [if-matched1], ..., [default])
Expand into a shell ‘case’ statement, where word is matched
against one or more patterns. if-matched is run if the
corresponding pattern matched word, else default is run.
— Macro: AS_DIRNAME ( file-name)
Output the directory portion of file-name. For example,
if $file is ‘/one/two/three’, the command
dir=`AS_DIRNAME(["$file"])` sets dir to ‘/one/two’.
— Macro: AS_IF ( test1, [run-if-true1], ..., [run-if-false])
Run shell code test1. If test1 exits with a zero status then
run shell code run-if-true1, else examine further tests. If no test
exits with a zero status, run shell code run-if-false, with
simplifications if either run-if-true1 or run-if-false1
is empty. For example,
AS_IF([test "$foo" = yes], [HANDLE_FOO([yes])],
[test "$foo" != no], [HANDLE_FOO([maybe])],
[echo foo not specified])
ensures any required macros of HANDLE_FOO
are expanded before the first test.
— Macro: AS_MKDIR_P ( file-name)
Make the directory file-name, including intervening directories
as necessary. This is equivalent to ‘mkdir -p file-name’,
except that it is portable to older versions of mkdir that
lack support for the -p option. Also, AS_MKDIR_P
succeeds if file-name is a symbolic link to an existing directory,
even though Posix is unclear whether ‘mkdir -p’ should
succeed in that case. If creation of file-name fails, exit the
script.
Also see the AC_PROG_MKDIR_P macro (see Particular Programs).
— Macro: AS_SHELL_SANITIZE
Initialize the shell suitably for configure scripts. This has
the effect of AS_BOURNE_COMPATIBLE, and sets some other
environment variables for predictable results from configuration tests.
For example, it sets LC_ALL to change to the default C locale.
See Special Shell Variables.
— Macro: AS_TR_CPP ( expression)
Transform expression into a valid right-hand side for a C #define.
For example:
# This outputs "#define HAVE_CHAR_P 1".
type="char *"
echo "#define AS_TR_CPP([HAVE_$type]) 1"
— Macro: AS_TR_SH ( expression)
Transform expression into a valid shell variable name. For example:
# This outputs "Have it!".
header="sys/some file.h"
AS_TR_SH([HAVE_$header])=yes
if test "$HAVE_sys_some_file_h" = yes; then echo "Have it!"; fi
— Macro: AS_SET_CATFILE ( var, dir, file)
Set the shell variable var to dir/file, but
optimizing the common cases (dir or file is ‘.’,
file is absolute, etc.).
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