Linux Shell Scripting Cookbook - Third Edition

Using loop inside awk

Awk supports a numeric for loop with a syntax similar to C:

    for(i=0;i<10;i++) { print $i ; } 

Awk also supports a list style for loop that will display the contents of an array:

    for(i in array) { print array[i]; } 

The following example shows how to collect data into an array and then display it. This script reads lines from /etc/password, splits them into fields at the : markers, and creates an array of names in which the index is the login ID and the value is the user's name:

    $ awk 'BEGIN {FS=":"} {nam[$1]=$5} END {for {i in nam} \
        {print i,nam[i]}}' /etc/passwd
    root root
    ftp FTP User
    userj Joe User