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(gcc-295.info)Environment Variables

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Environment Variables Affecting GCC
===================================

   This section describes several environment variables that affect how
GCC operates.  Some of them work by specifying directories or prefixes
to use when searching for various kinds of files. Some are used to
specify other aspects of the compilation environment.

   Note that you can also specify places to search using options such as
`-B', `-I' and `-L' (Note: Directory Options.).  These take
precedence over places specified using environment variables, which in
turn take precedence over those specified by the configuration of GCC.
Note: Driver.

`LANG'
`LC_CTYPE'
`LC_MESSAGES'
`LC_ALL'
     These environment variables control the way that GCC uses
     localization information that allow GCC to work with different
     national conventions.  GCC inspects the locale categories
     `LC_CTYPE' and `LC_MESSAGES' if it has been configured to do so.
     These locale categories can be set to any value supported by your
     installation.  A typical value is `en_UK' for English in the United
     Kingdom.

     The `LC_CTYPE' environment variable specifies character
     classification.  GCC uses it to determine the character boundaries
     in a string; this is needed for some multibyte encodings that
     contain quote and escape characters that would otherwise be
     interpreted as a string end or escape.

     The `LC_MESSAGES' environment variable specifies the language to
     use in diagnostic messages.

     If the `LC_ALL' environment variable is set, it overrides the value
     of `LC_CTYPE' and `LC_MESSAGES'; otherwise, `LC_CTYPE' and
     `LC_MESSAGES' default to the value of the `LANG' environment
     variable.  If none of these variables are set, GCC defaults to
     traditional C English behavior.

`TMPDIR'
     If `TMPDIR' is set, it specifies the directory to use for temporary
     files.  GCC 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'
     If `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 GCC cannot find the subprogram using the specified prefix, it
     tries looking in the usual places for the subprogram.

     The default value 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'), GCC tries replacing that beginning with the
     specified prefix to produce an alternate directory name.  Thus,
     with `-Bfoo/', GCC 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'
     The value of `COMPILER_PATH' is a colon-separated list of
     directories, much like `PATH'.  GCC tries the directories thus
     specified when searching for subprograms, if it can't find the
     subprograms using `GCC_EXEC_PREFIX'.

`LIBRARY_PATH'
     The value of `LIBRARY_PATH' is a colon-separated list of
     directories, much like `PATH'.  When configured as a native
     compiler, GCC tries the directories thus specified when searching
     for special linker files, if it can't find them using
     `GCC_EXEC_PREFIX'.  Linking using GCC 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'
     These environment variables pertain to particular languages.  Each
     variable's value is a colon-separated list of directories, much
     like `PATH'.  When GCC 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'
     If this variable is set, its value specifies how to output
     dependencies for Make based on the header files processed by the
     compiler.  This output looks much like the output from the `-M'
     option (Note: Preprocessor Options.), but it goes to a separate
     file, and is in addition to the usual results of compilation.

     The value of `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.

`LANG'
     This variable is used to pass locale information to the compiler.
     One way in which this information is used is to determine the
     character set to be used when character literals, string literals
     and comments are parsed in C and C++.  When the compiler is
     configured to allow multibyte characters, the following values for
     `LANG' are recognized:

    `C-JIS'
          Recognize JIS characters.

    `C-SJIS'
          Recognize SJIS characters.

    `C-EUCJP'
          Recognize EUCJP characters.

     If `LANG' is not defined, or if it has some other value, then the
     compiler will use mblen and mbtowc as defined by the default
     locale to recognize and translate multibyte characters.