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gawk: Comments

 
 1.1.5 Comments in 'awk' Programs
 --------------------------------
 
 A "comment" is some text that is included in a program for the sake of
 human readers; it is not really an executable part of the program.
 Comments can explain what the program does and how it works.  Nearly all
 programming languages have provisions for comments, as programs are
 typically hard to understand without them.
 
    In the 'awk' language, a comment starts with the number sign
 character ('#') and continues to the end of the line.  The '#' does not
 have to be the first character on the line.  The 'awk' language ignores
 the rest of a line following a number sign.  For example, we could have
 put the following into 'advice':
 
      # This program prints a nice, friendly message.  It helps
      # keep novice users from being afraid of the computer.
      BEGIN    { print "Don't Panic!" }
 
    You can put comment lines into keyboard-composed throwaway 'awk'
 programs, but this usually isn't very useful; the purpose of a comment
 is to help you or another person understand the program when reading it
 at a later time.
 
      CAUTION: As mentioned in ⇒One-shot, you can enclose short to
      medium-sized programs in single quotes, in order to keep your shell
      scripts self-contained.  When doing so, _don't_ put an apostrophe
      (i.e., a single quote) into a comment (or anywhere else in your
      program).  The shell interprets the quote as the closing quote for
      the entire program.  As a result, usually the shell prints a
      message about mismatched quotes, and if 'awk' actually runs, it
      will probably print strange messages about syntax errors.  For
      example, look at the following:
 
           $ awk 'BEGIN { print "hello" } # let's be cute'
           >
 
      The shell sees that the first two quotes match, and that a new
      quoted object begins at the end of the command line.  It therefore
      prompts with the secondary prompt, waiting for more input.  With
      Unix 'awk', closing the quoted string produces this result:
 
           $ awk '{ print "hello" } # let's be cute'
           > '
           error-> awk: can't open file be
           error->  source line number 1
 
      Putting a backslash before the single quote in 'let's' wouldn't
      help, because backslashes are not special inside single quotes.
      The next node describes the shell's quoting rules.
 
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