(gcc.info.gz) Environment Variables

 
 3.19 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' ( Directory Options).  These take precedence
 over places specified using environment variables, which in turn take
 precedence over those specified by the configuration of GCC.  
 Controlling the Compilation Driver `gcc' (gccint)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_GB.UTF-8' for English in the
      United Kingdom encoded in UTF-8.
 
      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_EXEC_PREFIX' is not set, GCC will attempt to figure out an
      appropriate prefix to use based on the pathname it was invoked
      with.
 
      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/' where
      PREFIX is the prefix to the installed compiler. In many cases
      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'
      (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. If a standard directory begins with the
      configured PREFIX then the value of PREFIX is replaced by
      `GCC_EXEC_PREFIX' when looking for header files.
 
 `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).
 
 `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.
 
 Some additional environments variables affect the behavior of the
 preprocessor.
 
 `CPATH'
 `C_INCLUDE_PATH'
 `CPLUS_INCLUDE_PATH'
 `OBJC_INCLUDE_PATH'
      Each variable's value is a list of directories separated by a
      special character, much like `PATH', in which to look for header
      files.  The special character, `PATH_SEPARATOR', is
      target-dependent and determined at GCC build time.  For Microsoft
      Windows-based targets it is a semicolon, and for almost all other
      targets it is a colon.
 
      `CPATH' specifies a list of directories to be searched as if
      specified with `-I', but after any paths given with `-I' options
      on the command line.  This environment variable is used regardless
      of which language is being preprocessed.
 
      The remaining environment variables apply only when preprocessing
      the particular language indicated.  Each specifies a list of
      directories to be searched as if specified with `-isystem', but
      after any paths given with `-isystem' options on the command line.
 
      In all these variables, an empty element instructs the compiler to
      search its current working directory.  Empty elements can appear
      at the beginning or end of a path.  For instance, if the value of
      `CPATH' is `:/special/include', that has the same effect as
      `-I. -I/special/include'.
 
 `DEPENDENCIES_OUTPUT'
      If this variable is set, its value specifies how to output
      dependencies for Make based on the non-system header files
      processed by the compiler.  System header files are ignored in the
      dependency output.
 
      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.
 
      In other words, this environment variable is equivalent to
      combining the options `-MM' and `-MF' ( Preprocessor
      Options), with an optional `-MT' switch too.
 
 `SUNPRO_DEPENDENCIES'
      This variable is the same as `DEPENDENCIES_OUTPUT' (see above),
      except that system header files are not ignored, so it implies
      `-M' rather than `-MM'.  However, the dependence on the main input
      file is omitted.   Preprocessor Options.
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