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Full Discussion: awk removing data before or after a pattern
Top Forums Shell Programming and Scripting awk removing data before or after a pattern Post 302443406 by agama on Sunday 8th of August 2010 07:05:09 PM
Old 08-08-2010
Quote:
Originally Posted by gvj
Could you pls explain why it is working??
His script is taking advantage of the fact that if the action part of a pattern-action pair is missing, the action {print;} is assumed. Further, !p is the same as saying 'p == 0' in the pattern portion of the statement. The value of an undefined variable is either 0 or "" depending on how it is used. To write the script in 'long form' might make more sense to you:

Code:
awk ' 
BEGIN { p = 0;}
p == 0 { print; }       # pattern not matched; print  (!p;)
/^03:00/ { p = 1; }  # pattern is matched, stop printing (exit(0) would be more efficient)
' file

Similarly, printing everything after the pattern line:
Code:
BEGIN { p = 0;}
/^03:00/ { p = 1; }  # pattern is matched, allow printing
p != 0 { print; }       # p;  in the original script
' file

This User Gave Thanks to agama For This Post:
gvj
 

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LEARN ABOUT DEBIAN

igawk

IGAWK(1)							 Utility Commands							  IGAWK(1)

NAME

       igawk - gawk with include files

SYNOPSIS

       igawk [ all gawk options ] -f program-file [ -- ] file ...
       igawk [ all gawk options ] [ -- ] program-text file ...

DESCRIPTION

       Igawk is a simple shell script that adds the ability to have ``include files'' to gawk(1).

       AWK programs for igawk are the same as for gawk, except that, in addition, you may have lines like

	      @include getopt.awk

       in your program to include the file getopt.awk from either the current directory or one of the other directories in the search path.

OPTIONS

       See gawk(1) for a full description of the AWK language and the options that gawk supports.

EXAMPLES

       cat << EOF > test.awk
       @include getopt.awk

       BEGIN {
	    while (getopt(ARGC, ARGV, "am:q") != -1)
		 ...
       }
       EOF

       igawk -f test.awk

SEE ALSO

       gawk(1)

       Effective AWK Programming, Edition 1.0, published by the Free Software Foundation, 1995.

AUTHOR

       Arnold Robbins (arnold@skeeve.com).

Free Software Foundation					    Nov 3 1999								  IGAWK(1)
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