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(libc.info)Standard Environment

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Standard Environment Variables
------------------------------

   These environment variables have standard meanings.  This doesn't
mean that they are always present in the environment; but if these
variables _are_ present, they have these meanings.  You shouldn't try
to use these environment variable names for some other purpose.

`HOME'
     This is a string representing the user's "home directory", or
     initial default working directory.

     The user can set `HOME' to any value.  If you need to make sure to
     obtain the proper home directory for a particular user, you should
     not use `HOME'; instead, look up the user's name in the user
     database (Note: User Database).

     For most purposes, it is better to use `HOME', precisely because
     this lets the user specify the value.

`LOGNAME'
     This is the name that the user used to log in.  Since the value in
     the environment can be tweaked arbitrarily, this is not a reliable
     way to identify the user who is running a program; a function like
     `getlogin' (Note: Who Logged In) is better for that purpose.

     For most purposes, it is better to use `LOGNAME', precisely because
     this lets the user specify the value.

`PATH'
     A "path" is a sequence of directory names which is used for
     searching for a file.  The variable `PATH' holds a path used for
     searching for programs to be run.

     The `execlp' and `execvp' functions (Note: Executing a File) use
     this environment variable, as do many shells and other utilities
     which are implemented in terms of those functions.

     The syntax of a path is a sequence of directory names separated by
     colons.  An empty string instead of a directory name stands for the
     current directory (Note: Working Directory).

     A typical value for this environment variable might be a string
     like:

          :/bin:/etc:/usr/bin:/usr/new/X11:/usr/new:/usr/local/bin

     This means that if the user tries to execute a program named `foo',
     the system will look for files named `foo', `/bin/foo',
     `/etc/foo', and so on.  The first of these files that exists is
     the one that is executed.

`TERM'
     This specifies the kind of terminal that is receiving program
     output.  Some programs can make use of this information to take
     advantage of special escape sequences or terminal modes supported
     by particular kinds of terminals.  Many programs which use the
     termcap library (Note: Find.
) use the `TERM' environment variable, for example.

`TZ'
     This specifies the time zone.  Note: TZ Variable, for
     information about the format of this string and how it is used.

`LANG'
     This specifies the default locale to use for attribute categories
     where neither `LC_ALL' nor the specific environment variable for
     that category is set.  Note: Locales, for more information about
     locales.

`LC_ALL'
     If this environment variable is set it overrides the selection for
     all the locales done using the other `LC_*' environment variables.
     The value of the other `LC_*' environment variables is simply
     ignored in this case.

`LC_COLLATE'
     This specifies what locale to use for string sorting.

`LC_CTYPE'
     This specifies what locale to use for character sets and character
     classification.

`LC_MESSAGES'
     This specifies what locale to use for printing messages and to
     parse responses.

`LC_MONETARY'
     This specifies what locale to use for formatting monetary values.

`LC_NUMERIC'
     This specifies what locale to use for formatting numbers.

`LC_TIME'
     This specifies what locale to use for formatting date/time values.

`NLSPATH'
     This specifies the directories in which the `catopen' function
     looks for message translation catalogs.

`_POSIX_OPTION_ORDER'
     If this environment variable is defined, it suppresses the usual
     reordering of command line arguments by `getopt' and `argp_parse'.
     Note: Argument Syntax.