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gawk: AWKPATH Variable

 2.5.1 The 'AWKPATH' Environment Variable
 The previous minor node described how 'awk' program files can be named
 on the command line with the '-f' option.  In most 'awk'
 implementations, you must supply a precise pathname for each program
 file, unless the file is in the current directory.  But with 'gawk', if
 the file name supplied to the '-f' or '-i' options does not contain a
 directory separator '/', then 'gawk' searches a list of directories
 (called the "search path") one by one, looking for a file with the
 specified name.
    The search path is a string consisting of directory names separated
 by colons.(1)  'gawk' gets its search path from the 'AWKPATH'
 environment variable.  If that variable does not exist, or if it has an
 empty value, 'gawk' uses a default path (described shortly).
    The search path feature is particularly helpful for building
 libraries of useful 'awk' functions.  The library files can be placed in
 a standard directory in the default path and then specified on the
 command line with a short file name.  Otherwise, you would have to type
 the full file name for each file.
    By using the '-i' or '-f' options, your command-line 'awk' programs
 can use facilities in 'awk' library files (⇒Library Functions).
 Path searching is not done if 'gawk' is in compatibility mode.  This is
 true for both '--traditional' and '--posix'.  ⇒Options.
    If the source code file is not found after the initial search, the
 path is searched again after adding the suffix '.awk' to the file name.
    'gawk''s path search mechanism is similar to the shell's.  (See 'The
 Bourne-Again SHell manual' (
 It treats a null entry in the path as indicating the current directory.
 (A null entry is indicated by starting or ending the path with a colon
 or by placing two colons next to each other ['::'].)
      NOTE: To include the current directory in the path, either place
      '.' as an entry in the path or write a null entry in the path.
      Different past versions of 'gawk' would also look explicitly in the
      current directory, either before or after the path search.  As of
      version 4.1.2, this no longer happens; if you wish to look in the
      current directory, you must include '.' either as a separate entry
      or as a null entry in the search path.
    The default value for 'AWKPATH' is '.:/usr/local/share/awk'.(2)
 Since '.' is included at the beginning, 'gawk' searches first in the
 current directory and then in '/usr/local/share/awk'.  In practice, this
 means that you will rarely need to change the value of 'AWKPATH'.
    ⇒Shell Startup Files, for information on functions that help
 to manipulate the 'AWKPATH' variable.
    'gawk' places the value of the search path that it used into
 'ENVIRON["AWKPATH"]'.  This provides access to the actual search path
 value from within an 'awk' program.
    Although you can change 'ENVIRON["AWKPATH"]' within your 'awk'
 program, this has no effect on the running program's behavior.  This
 makes sense: the 'AWKPATH' environment variable is used to find the
 program source files.  Once your program is running, all the files have
 been found, and 'gawk' no longer needs to use 'AWKPATH'.
    ---------- Footnotes ----------
    (1) Semicolons on MS-Windows.
    (2) Your version of 'gawk' may use a different directory; it will
 depend upon how 'gawk' was built and installed.  The actual directory is
 the value of '$(datadir)' generated when 'gawk' was configured.  You
 probably don't need to worry about this, though.
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