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5.2.2 Generic Program and File Checks

These macros are used to find programs not covered by the “particular” test macros. If you need to check the behavior of a program as well as find out whether it is present, you have to write your own test for it (see Writing Tests). By default, these macros use the environment variable PATH. If you need to check for a program that might not be in the user's PATH, you can pass a modified path to use instead, like this: 

     AC_PATH_PROG([INETD], [inetd], [/usr/libexec/inetd],
                  [$PATH$PATH_SEPARATOR/usr/libexec$PATH_SEPARATOR]dnl
     [/usr/sbin$PATH_SEPARATOR/usr/etc$PATH_SEPARATOR/etc])

You are strongly encouraged to declare the variable passed to AC_CHECK_PROG etc. as precious, See Setting Output Variables, AC_ARG_VAR, for more details.

— Macro: AC_CHECK_PROG (variable, prog-to-check-for, value-if-found, [value-if-not-found], [path = `$PATH'], [reject])

Check whether program prog-to-check-for exists in path. If it is found, set variable to value-if-found, otherwise to value-if-not-found, if given. Always pass over reject (an absolute file name) even if it is the first found in the search path; in that case, set variable using the absolute file name of the prog-to-check-for found that is not reject. If variable was already set, do nothing. Calls AC_SUBST for variable.

— Macro: AC_CHECK_PROGS (variable, progs-to-check-for, [value-if-not-found], [path = `$PATH'])

Check for each program in the blank-separated list progs-to-check-for existing in the path. If one is found, set variable to the name of that program. Otherwise, continue checking the next program in the list. If none of the programs in the list are found, set variable to value-if-not-found; if value-if-not-found is not specified, the value of variable is not changed. Calls AC_SUBST for variable.

— Macro: AC_CHECK_TARGET_TOOL (variable, prog-to-check-for, [value-if-not-found], [path = `$PATH'])

Like AC_CHECK_PROG, but first looks for prog-to-check-for with a prefix of the target type as determined by AC_CANONICAL_TARGET, followed by a dash (see Canonicalizing). If the tool cannot be found with a prefix, and if the build and target types are equal, then it is also searched for without a prefix.

As noted in Specifying the system type, the target is rarely specified, because most of the time it is the same as the host: it is the type of system for which any compiler tool in the package produces code. What this macro looks for is, for example, a tool (assembler, linker, etc.) that the compiler driver (gcc for the GNU C Compiler) uses to produce objects, archives or executables.

— Macro: AC_CHECK_TOOL (variable, prog-to-check-for, [value-if-not-found], [path = `$PATH'])

Like AC_CHECK_PROG, but first looks for prog-to-check-for with a prefix of the host type as specified by --host, followed by a dash. For example, if the user runs `configure --build=x86_64-gnu --host=i386-gnu', then this call: 

          AC_CHECK_TOOL([RANLIB], [ranlib], [:])

sets RANLIB to i386-gnu-ranlib if that program exists in path, or otherwise to `ranlib' if that program exists in path, or to `:' if neither program exists.

When cross-compiling, this macro will issue a warning if no program prefixed with the host type could be found. For more information, see Specifying the system type.

— Macro: AC_CHECK_TARGET_TOOLS (variable, progs-to-check-for, [value-if-not-found], [path = `$PATH'])

Like AC_CHECK_TARGET_TOOL, each of the tools in the list progs-to-check-for are checked with a prefix of the target type as determined by AC_CANONICAL_TARGET, followed by a dash (see Canonicalizing). If none of the tools can be found with a prefix, and if the build and target types are equal, then the first one without a prefix is used. If a tool is found, set variable to the name of that program. If none of the tools in the list are found, set variable to value-if-not-found; if value-if-not-found is not specified, the value of variable is not changed. Calls AC_SUBST for variable.

— Macro: AC_CHECK_TOOLS (variable, progs-to-check-for, [value-if-not-found], [path = `$PATH'])

Like AC_CHECK_TOOL, each of the tools in the list progs-to-check-for are checked with a prefix of the host type as determined by AC_CANONICAL_HOST, followed by a dash (see Canonicalizing). If none of the tools can be found with a prefix, then the first one without a prefix is used. If a tool is found, set variable to the name of that program. If none of the tools in the list are found, set variable to value-if-not-found; if value-if-not-found is not specified, the value of variable is not changed. Calls AC_SUBST for variable.

When cross-compiling, this macro will issue a warning if no program prefixed with the host type could be found. For more information, see Specifying the system type.

— Macro: AC_PATH_PROG (variable, prog-to-check-for, [value-if-not-found], [path = `$PATH'])

Like AC_CHECK_PROG, but set variable to the absolute name of prog-to-check-for if found.

— Macro: AC_PATH_PROGS (variable, progs-to-check-for, [value-if-not-found], [path = `$PATH'])

Like AC_CHECK_PROGS, but if any of progs-to-check-for are found, set variable to the absolute name of the program found.

— Macro: AC_PATH_PROGS_FEATURE_CHECK (variable, progs-to-check-for, feature-test, [action-if-not-found], [path = `$PATH'])

This macro was introduced in Autoconf 2.62. If variable is not empty, then set the cache variable $ac_cv_path_variable to its value. Otherwise, check for each program in the blank-separated list progs-to-check-for existing in path. For each program found, execute feature-test with $ac_path_variable set to the absolute name of the candidate program. If no invocation of feature-test sets the shell variable $ac_cv_path_variable, then action-if-not-found is executed. feature-test will be run even when ac_cv_path_variable is set, to provide the ability to choose a better candidate found later in path; to accept the current setting and bypass all futher checks, feature-test can execute ac_path_variable_found=:.

Note that this macro has some subtle differences from AC_CHECK_PROGS. It is designed to be run inside AC_CACHE_VAL, therefore, it should have no side effects. In particular, variable is not set to the final value of ac_cv_path_variable, nor is AC_SUBST automatically run. Also, on failure, any action can be performed, whereas AC_CHECK_PROGS only performs variable=value-if-not-found.

Here is an example, similar to what Autoconf uses in its own configure script. It will search for an implementation of m4 that supports the indir builtin, even if it goes by the name gm4 or is not the first implementation on PATH. 

          AC_CACHE_CHECK([for m4 that supports indir], [ac_cv_path_M4],
            [AC_PATH_PROGS_FEATURE_CHECK([M4], [m4 gm4],
              [[m4out=`echo 'changequote([,])indir([divnum])' | $ac_path_M4`
                test "x$m4out" = x0 \
                && ac_cv_path_M4=$ac_path_M4 ac_path_M4_found=:]],
              [AC_MSG_ERROR([could not find m4 that supports indir])])])
          AC_SUBST([M4], [$ac_cv_path_M4])
— Macro: AC_PATH_TARGET_TOOL (variable, prog-to-check-for, [value-if-not-found], [path = `$PATH'])

Like AC_CHECK_TARGET_TOOL, but set variable to the absolute name of the program if it is found.

— Macro: AC_PATH_TOOL (variable, prog-to-check-for, [value-if-not-found], [path = `$PATH'])

Like AC_CHECK_TOOL, but set variable to the absolute name of the program if it is found.

When cross-compiling, this macro will issue a warning if no program prefixed with the host type could be found. For more information, see Specifying the system type.