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Full Discussion: awk syntax
Top Forums UNIX for Dummies Questions & Answers awk syntax Post 302398294 by pludi on Wednesday 24th of February 2010 07:14:29 AM
Old 02-24-2010
The dollar sign '$' tells the shell that the characters trailing it form variable name. Besides the usual variables, there are also special ones like $@, $*, and $0 to $9.

Your sed command gets transformed like this:
Code:
cat file.txt |sed -n "/$a/p"
cat file.txt |sed -n /hello/p

With the awk command you've given, the shell tries to interpolate the $2 and $4 with the appropriate positional parameters, which probably aren't set. So the transformation would look like this:
Code:
cat file.txt | awk "/$a/{print $2,$4}"
cat file.txt | awk /hello/{print ,}

But fear not, there is help. awk supports the -v switch, which allows one to set awk variables from outside the awk program. So if you rewrite the line as
Code:
awk -vsearch=$a '$0 ~ search {print $2,$4}' file.txt

everything should work. And you're even saving on time since you don't have to run cat unnecessarily.
 

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LEARN ABOUT CENTOS

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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