This section describes several environment variables that affect how GNU CC operates. They work by specifying directories or prefixes to use when searching for various kinds of files.
Note that you can also specify places to search using options such as `-B', `-I' and `-L' (see section Options for Directory Search). These take precedence over places specified using environment variables, which in turn take precedence over those specified by the configuration of GNU CC.
TMPDIR
TMPDIR
is set, it specifies the directory to use for temporary
files. GNU CC uses temporary files to hold the output of one stage of
compilation which is to be used as input to the next stage: for example,
the output of the preprocessor, which is the input to the compiler
proper.
GCC_EXEC_PREFIX
GCC_EXEC_PREFIX
is set, it specifies a prefix to use in the
names of the subprograms executed by the compiler. No slash is added
when this prefix is combined with the name of a subprogram, but you can
specify a prefix that ends with a slash if you wish.
If GNU CC cannot find the subprogram using the specified prefix, it
tries looking in the usual places for the subprogram.
The default of GCC_EXEC_PREFIX
is
`prefix/lib/gcc-lib/', where prefix is the value
of prefix
when you ran the `configure' script.
Other prefixes specified with `-B' take precedence over this prefix.
This prefix is also used for finding files such as `crt0.o' that are
used for linking.
In addition, the prefix is used in an unusual way in finding the
directories to search for header files. For each of the standard
directories whose name normally begins with `/usr/local/lib/gcc-lib'
(more precisely, with the value of GCC_INCLUDE_DIR
), GNU CC tries
replacing that beginning with the specified prefix to produce an
alternate directory name. Thus, with `-Bfoo/', GNU CC will search
`foo/bar' where it would normally search `/usr/local/lib/bar'.
These alternate directories are searched first; the standard directories
come next.
COMPILER_PATH
COMPILER_PATH
is a colon-separated list of
directories, much like PATH
. GNU CC tries the directories thus
specified when searching for subprograms, if it can't find the
subprograms using GCC_EXEC_PREFIX
.
LIBRARY_PATH
LIBRARY_PATH
is a colon-separated list of
directories, much like PATH
. When configured as a native compiler,
GNU CC tries the directories thus specified when searching for special
linker files, if it can't find them using GCC_EXEC_PREFIX
. Linking
using GNU CC also uses these directories when searching for ordinary
libraries for the `-l' option (but directories specified with
`-L' come first).
C_INCLUDE_PATH
CPLUS_INCLUDE_PATH
OBJC_INCLUDE_PATH
PATH
. When GNU CC searches for header files, it tries the
directories listed in the variable for the language you are using, after
the directories specified with `-I' but before the standard header
file directories.
DEPENDENCIES_OUTPUT
DEPENDENCIES_OUTPUT
can be just a file name, in
which case the Make rules are written to that file, guessing the target
name from the source file name. Or the value can have the form
`file target', in which case the rules are written to
file file using target as the target name.