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Full Discussion: awk, array indexing
Top Forums UNIX for Dummies Questions & Answers awk, array indexing Post 302678079 by neutronscott on Friday 27th of July 2012 07:54:37 AM
Old 07-27-2012
Just the indexing? I will try to explain all of it.

Firstly, it is often (and better) written:

Code:
nawk -F= '!a[$1]++' filename

Each record (a line here) is split into fields. The first field is addressed with $1, the second with $2, and so on. The entire record is $0. So it uses $1 as the index into the array called a. Stored there is the count of occurances (the ++ operator increments the value). The first time it is seen though, it evaluates as 0. (It returns 0 but is then set to 1, called post-increment). So the ! operator will negate that. So it will only print the first line where $1 is unique, because each successive iteration of that same $1 will then become 0 after !.
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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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