AWK Linux command

why awk?

awk is small, fast, and simple, unlike, say, perl. awk also has a clean comprehensible C-like input language, unlike, say, perl. And while it can’t do everything you can do in perl, it can do most things that are actually text processing, and it’s much easier to work with.

what do you do?

In its simplest usage awk is meant for processing column-oriented text data, such as tables, presented to it on standard input. The variables $1, $2, and so forth are the contents of the first, second, etc. column of the current input line. For example, to print the second column of a file, you might use the following simple awk script:

        awk < file '{ print $2 }'

This means “on every line, print the second field”.

To print the second and third columns, you might use

        awk < file '{ print $2, $3 }'

Input separator

By default awk splits input lines into fields based on whitespace, that is, spaces and tabs. You can change this by using the -F option to awk and supplying another character. For instance, to print the home directories of all users on the system, you might do

        awk < /etc/passwd -F: '{ print $6 }'

since the password file has fields delimited by colons and the home directory is the 6th field.

Print column1, column5 and column7 of a data file or output of any columns list

$awk ‘{print $1, $5, $7}’ data_file

$cat file_name |awk ‘{print $1 $5 $7}’

$ls –al |awk ‘{print $1, $5, $7}’ — Prints file_permissions,size and date

Syntax of running an awk program

Awk ‘program’ input file(s)

List all files names whose file size greater than zero.

$ls –al |awk ‘$5 > 0 {print $9}’

List all files whose file size equal to 512bytes.

$ls –al |awk ‘$5 == 0 {print $9}’

print all lines

$awk ‘{print }’ file_name

$awk ‘{print 0}’ file_name

Number of lines in a file

$awk ‘ END {print NR}’ file_name

Number of columns in each row of a file

$awk ‘ {print NF’} file_name

Sort the output of file and eliminate duplicate rows

$awk ‘{print $1, $5, $7}’ |sort –u

List all file names whose file size is greater than 512bytes and owner is “oracle”

$ls –al |awk ‘$3 == “oracle” && $5 > 512 {print $9}’

List all file names whose owner could be either “oracle” or “root”

$ls –al |awk ‘$3 == “oracle” || $3 == “root” {print $9}’

list all the files whose owner is not “oracle

$ls –al |awk ‘$3 != “oracle” {print $9}’

List all lines which has atlease one or more characters

$awk ‘NF > 0 {print }’ file_name

List all lines longer that 50 characters

$awk ‘length($0) > 50 ‘{print }’ file_name

List first two columns

$awk ‘{print $1, $2}’ file_name

Swap first two columns of a file and print

$awk ‘{temp = $1; $1 = $2; $2 = temp; print }’ file_name

Replace first column as “ORACLE” in a data file

$awk ‘{$1 = “ORACLE”; print }’ data_file

Remove first column values in a data file

$awk ‘{$1 =””; print }’ data_file

Calculate total size of a directory in Mb

$ls –al |awk ‘{total +=$5};END {print “Total size: ” total/1024/1024 ” Mb”}’

Calculate total size of a directory including sub directories in Mb

$ls –lR |awk ‘{total +=$5};END {print “Total size: ” total/1024/1024 ” Mb”}’

Find largest file in a directory including sub directories

$ls –lR |awk ‘{print $5 “\t” $9}’ |sort –n |tail -1