awk Commands, Examples & Meaning

awk regular expressions

gsub

Global substitution for the pattern in target
gsub(regexp, replacement [, target])

gensub()

it is a general substitution function providing more features than the standard sub() and gsub() functions- the ability to specify components of a regexp in the replacement text

localhost ~]$ df  | awk ‘{ print gensub(/\%/, ” Percent”, 1) }’
Filesystem              1K-blocks     Used Available Use Percent Mounted on
/dev/mapper/fedora-root  51475068 10831316  38005928  23 Percent /
devtmpfs                  1956180        0   1956180   0 Percent /dev
/dev/sda9                  487652   123767    334189  28 Percent /boot
/dev/mapper/fedora-home  58642620 51118476   4522188  92 Percent /home
/dev/sda2                   98304    66006     32298  68 Percent /boot/efi

index(in, find)

Find the index value of a  sub string .

localhost ~]$ awk ‘BEGIN { print index(“SomeLongString”, “tr”) }’
10

length([string])

Find the length of string,  length of lines in the example below

localhost ~]$ awk ‘ { print length($0) }’ testfile
31
29
29
29

match(string, regexp [, array])

match alphabet characters in file  and print whole line

localhost ~]$ awk ‘ match($0, /[a-z]/) { print $0 }’ testfile
column1 column2 column3 column4

split(string, array [, fieldsep [, seps ] ])

Split a list of rpm names at  dashes.
content of the files – rpms
libhbalinux-1.0.16-2.fc20.x86_64
gucharmap-3.10.1-1.fc20.x86_64
libplist-1.11-2.fc20.x86_64
libgcc-4.8.3-7.fc20.i686
glx-utils-8.1.0-4.fc20.x86_64
vlgothic-fonts-20140801-1.fc20.noarch
Split along  dashes , keep in array and  print selected index values , keep separators in a array called sep .

localhost ~]$ cat rpms | awk ‘{split($0, ary, “-“, seps) ; print ary[1],ary[2],ary[3]}’
libhbalinux 1.0.16 2.fc20.x86_64
gucharmap 3.10.1 1.fc20.x86_64
libplist 1.11 2.fc20.x86_64
libgcc 4.8.3 7.fc20.i686
glx utils 8.1.0
vlgothic fonts 20140801

print both arrays , ary and sep , the seprator arry contents

localhost ~]$ cat rpms | awk ‘{split($0, ary, “-“, seps) ; print ary[1],ary[2],ary[3],seps[1],seps[2]}’
libhbalinux 1.0.16 2.fc20.x86_64 —
gucharmap 3.10.1 1.fc20.x86_64 —
libplist 1.11 2.fc20.x86_64 —
libgcc 4.8.3 7.fc20.i686 —
glx utils 8.1.0 —
vlgothic fonts 20140801 —

sub(regexp, replacement [, target])

Substitute a pattern with a string ,  in the example below replace dash followed by any number with –>

localhost ~]$ cat rpms | awk ‘sub(/-[0-9]/, ” –> ” )’;
libhbalinux –> .0.16-2.fc20.x86_64
gucharmap –> .10.1-1.fc20.x86_64
libplist –> .11-2.fc20.x86_64
libgcc –> .8.3-7.fc20.i686
glx-utils –> .1.0-4.fc20.x86_64
vlgothic-fonts –> 0140801-1.fc20.noarch

substr(string, start [, length ])

Get a  substring of defined length  from  a given position
Lets use this file having two fields
localhost ~]$ cat nums
123456789 abcdef
find 3rd position and print two values from first field.

localhost ~]$ awk ‘{print substr($1,3,2) }’ nums
34
find 3rd position and print two values from second field.
localhost ~]$ awk ‘{print substr($2,3,2) }’ nums
cd

tolower(string)

Convert alphabet string into lower case

tolower(“MiXeD cAsE 123”) returns “mixed case 123”.
Changing entire files to lowercase in the example below

localhost ~]$ cat letters
This is Just Some Random Text Here ..

localhost ~]$ awk ‘{ print tolower($0)}’ letters

this is just some random text here ..

toupper(string)
Convert alphabet string into upper case

localhost ~]$ awk ‘{ print toupper($0)}’ letters

THIS IS JUST SOME RANDOM TEXT HERE ..

Selective fields can be used for this operation, to make only first field as upper case:

awk ‘{ print toupper($1)}’ letters
THIS

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