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(libc.info.gz) Environment Variables

 
 25.4.2 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 ( 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' ( 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 ( 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 ( 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 ( Find (termcap)Finding a Terminal
      Description.) use the 'TERM' environment variable, for example.
 
 'TZ'
 
      This specifies the time zone.   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.   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'.
       Argument Syntax.
 

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(libc.info.gz) Environment Access

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