File: gawk.info,  Node: Shell Quoting,  Next: Isnumeric Function,  Prev: Readfile Function,  Up: General Functions

10.2.9 Quoting Strings to Pass to the Shell
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Michael Brennan offers the following programming pattern, which he uses
frequently:

     #! /bin/sh

     awkp='
        ...
        '

     INPUT_PROGRAM | awk "$awkp" | /bin/sh

   For example, a program of his named 'flac-edit' has this form:

     $ flac-edit -song="Whoope! That's Great" file.flac

   It generates the following output, which is to be piped to the shell
('/bin/sh'):

     chmod +w file.flac
     metaflac --remove-tag=TITLE file.flac
     LANG=en_US.88591 metaflac --set-tag=TITLE='Whoope! That'"'"'s Great' file.flac
     chmod -w file.flac

   Note the need for shell quoting.  The function 'shell_quote()' does
it.  'SINGLE' is the one-character string '"'"' and 'QSINGLE' is the
three-character string '"\"'\""':

     # shell_quote --- quote an argument for passing to the shell

     function shell_quote(s,             # parameter
         SINGLE, QSINGLE, i, X, n, ret)  # locals
     {
         if (s == "")
             return "\"\""

         SINGLE = "\x27"  # single quote
         QSINGLE = "\"\x27\""
         n = split(s, X, SINGLE)

         ret = SINGLE X[1] SINGLE
         for (i = 2; i <= n; i++)
             ret = ret QSINGLE SINGLE X[i] SINGLE

         return ret
     }