Info Catalog gawk: More Complex gawk: Getting Started gawk: Other Features

gawk: Statements/Lines

 
 1.6 'awk' Statements Versus Lines
 =================================
 
 Most often, each line in an 'awk' program is a separate statement or
 separate rule, like this:
 
      awk '/12/  { print $0 }
           /21/  { print $0 }' mail-list inventory-shipped
 
    However, 'gawk' ignores newlines after any of the following symbols
 and keywords:
 
      ,    {    ?    :    ||    &&    do    else
 
 A newline at any other point is considered the end of the statement.(1)
 
    If you would like to split a single statement into two lines at a
 point where a newline would terminate it, you can "continue" it by
 ending the first line with a backslash character ('\').  The backslash
 must be the final character on the line in order to be recognized as a
 continuation character.  A backslash is allowed anywhere in the
 statement, even in the middle of a string or regular expression.  For
 example:
 
      awk '/This regular expression is too long, so continue it\
       on the next line/ { print $1 }'
 
 We have generally not used backslash continuation in our sample
 programs.  'gawk' places no limit on the length of a line, so backslash
 continuation is never strictly necessary; it just makes programs more
 readable.  For this same reason, as well as for clarity, we have kept
 most statements short in the programs presented throughout the Info
 file.  Backslash continuation is most useful when your 'awk' program is
 in a separate source file instead of entered from the command line.  You
 should also note that many 'awk' implementations are more particular
 about where you may use backslash continuation.  For example, they may
 not allow you to split a string constant using backslash continuation.
 Thus, for maximum portability of your 'awk' programs, it is best not to
 split your lines in the middle of a regular expression or a string.
 
      CAUTION: _Backslash continuation does not work as described with
      the C shell._  It works for 'awk' programs in files and for
      one-shot programs, _provided_ you are using a POSIX-compliant
      shell, such as the Unix Bourne shell or Bash.  But the C shell
      behaves differently!  There you must use two backslashes in a row,
      followed by a newline.  Note also that when using the C shell,
      _every_ newline in your 'awk' program must be escaped with a
      backslash.  To illustrate:
 
           % awk 'BEGIN { \
           ?   print \\
           ?       "hello, world" \
           ? }'
           -| hello, world
 
      Here, the '%' and '?' are the C shell's primary and secondary
      prompts, analogous to the standard shell's '$' and '>'.
 
      Compare the previous example to how it is done with a
      POSIX-compliant shell:
 
           $ awk 'BEGIN {
           >   print \
           >       "hello, world"
           > }'
           -| hello, world
 
    'awk' is a line-oriented language.  Each rule's action has to begin
 on the same line as the pattern.  To have the pattern and action on
 separate lines, you _must_ use backslash continuation; there is no other
 option.
 
    Another thing to keep in mind is that backslash continuation and
 comments do not mix.  As soon as 'awk' sees the '#' that starts a
 comment, it ignores _everything_ on the rest of the line.  For example:
 
      $ gawk 'BEGIN { print "dont panic" # a friendly \
      >                                    BEGIN rule
      > }'
      error-> gawk: cmd. line:2:                BEGIN rule
      error-> gawk: cmd. line:2:                ^ syntax error
 
 In this case, it looks like the backslash would continue the comment
 onto the next line.  However, the backslash-newline combination is never
 even noticed because it is "hidden" inside the comment.  Thus, the
 'BEGIN' is noted as a syntax error.
 
    When 'awk' statements within one rule are short, you might want to
 put more than one of them on a line.  This is accomplished by separating
 the statements with a semicolon (';').  This also applies to the rules
 themselves.  Thus, the program shown at the start of this minor node
 could also be written this way:
 
      /12/ { print $0 } ; /21/ { print $0 }
 
      NOTE: The requirement that states that rules on the same line must
      be separated with a semicolon was not in the original 'awk'
      language; it was added for consistency with the treatment of
      statements within an action.
 
    ---------- Footnotes ----------
 
    (1) The '?' and ':' referred to here is the three-operand conditional
 expression described in Conditional Exp.  Splitting lines after
 '?' and ':' is a minor 'gawk' extension; if '--posix' is specified
 (Options), then this extension is disabled.
 

Info Catalog gawk: More Complex gawk: Getting Started gawk: Other Features