How do I read a text file using awk pattern scanning and text processing language under Linux / Unix like operating systems?
The default syntax to read a text file line-by-line using awk is as follows:
### note '{ print }' '{ print $0 }' '1' all are same ### awk '{ print }' /path/to/file awk '{}1' /path/to/file awk '1' /path/to/file awk '{ print $0 }' /path/to/file awk '{}1' /etc/passwd awk '{print $0}' /etc/hosts awk '{print}' /etc/hosts
Sample outputs:
127.0.0.1 localhost 192.168.1.5 wks01 # The following lines are desirable for IPv6 capable hosts ::1 ip6-localhost ip6-loopback fe00::0 ip6-localnet ff00::0 ip6-mcastprefix ff02::1 ip6-allnodes ff02::2 ip6-allrouters 192.168.1.10 nas01 192.168.1.11 nas02 192.168.1.12 nas03 192.168.2.50 nfs2.vmware.nixcraft.net.in nfs2v 192.168.2.51 nfs1.vmware.nixcraft.net.in nfs1v 172.168.232.50 nfs1.kvm.nixcraft.net.in nfs1k 172.168.232.51 nfs2.kvm.nixcraft.net.in nfs2k
The print command is used to display text on screen. The simplest form of this command:
awk '{ print }' filename
This displays the contents of the current record. However, in AWK, records are broken down into fields, and these can be displayed separately. To see 1st field, enter:
awk '{ print $1 }' filename
To see first and fourth fields of the current record, enter:
awk '{ print $1, $3 }' filename
You can set the output field separator (OFS) whose default value is a single space character using the -F option as follows:
### set OFS to : ### ### print user name, home directory and shell ### awk -F: '{ print $1 " users home directory set to \"" $6 "\" with " $7 " as login shell" }' /etc/passwd
Sample outputs:
root users home directory set to "/root" with /bin/bash as login shell daemon users home directory set to "/usr/sbin" with /bin/sh as login shell bin users home directory set to "/bin" with /bin/sh as login shell sys users home directory set to "/dev" with /bin/sh as login shell sync users home directory set to "/bin" with /bin/sync as login shell games users home directory set to "/usr/games" with /bin/sh as login shell man users home directory set to "/var/cache/man" with /bin/sh as login shell lp users home directory set to "/var/spool/lpd" with /bin/sh as login shell mail users home directory set to "/var/mail" with /bin/sh as login shell news users home directory set to "/var/spool/news" with /bin/sh as login shell uucp users home directory set to "/var/spool/uucp" with /bin/sh as login shell proxy users home directory set to "/bin" with /bin/sh as login shell www-data users home directory set to "/var/www" with /bin/sh as login shell backup users home directory set to "/var/backups" with /bin/sh as login shell list users home directory set to "/var/list" with /bin/sh as login shell irc users home directory set to "/var/run/ircd" with /bin/sh as login shell gnats users home directory set to "/var/lib/gnats" with /bin/sh as login shell nobody users home directory set to "/nonexistent" with /bin/sh as login shell libuuid users home directory set to "/var/lib/libuuid" with /bin/sh as login shell messagebus users home directory set to "/var/run/dbus" with /bin/false as login shell Debian-exim users home directory set to "/var/spool/exim4" with /bin/false as login shell statd users home directory set to "/var/lib/nfs" with /bin/false as login shell avahi-autoipd users home directory set to "/var/lib/avahi-autoipd" with /bin/false as login shell avahi users home directory set to "/var/run/avahi-daemon" with /bin/false as login shell usbmux users home directory set to "/home/usbmux" with /bin/false as login shell Debian-gdm users home directory set to "/var/lib/gdm3" with /bin/false as login shell saned users home directory set to "/home/saned" with /bin/false as login shell hplip users home directory set to "/var/run/hplip" with /bin/false as login shell vivek users home directory set to "/home/vivek" with /bin/bash as login shell bind users home directory set to "/var/cache/bind" with /bin/false as login shell haldaemon users home directory set to "/var/run/hald" with /bin/false as login shell sshd users home directory set to "/var/run/sshd" with /usr/sbin/nologin as login shell mysql users home directory set to "/var/lib/mysql" with /bin/false as login shell radvd users home directory set to "/var/run/radvd" with /bin/false as login shell
The commands "print" and "print $0" are identical in functionality.
Conditional awk printing
The awk syntax is as follows:
awk 'condition { action }' filename awk '1 == /match/ { action }' filename awk '1 == /match/ { print $0 }' filename awk 'pattern { action }' filename
If first field match to vivek print the entire line:
$ awk -F: '1 == /vivek/ { print $0}' /etc/passwd
OR,
$ awk -F: '/vivek/ { print $0}' /etc/passwd
For more information go through awk man page:
$ man awk
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{ 1 comment… read it below or add one }
To see first and fourth fields of the current record, enter:
awk ‘{ print $1, $3 }’ filename
fourth -> third