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AWK - Part 3 Cheat Sheet (DRAFT) by

This is a draft cheat sheet. It is a work in progress and is not finished yet.

Semicolon in AWK

As in many progra­mming languages like Java, the semicolon marks the end of one stateùent and the begin of another one.
 
awke '{print $1 ; print $0}' awk.txt 
 >>> AWK 
 >>> AWK is awesome 
 >>> Let 
 >>> Let learn AWK together 
 ...

The special variable FS

We can put the field separator within an AWK program vy assigning a value to the special variable FS.
 
awk 'BEGIN {FS =","} {print $2}' 
 Yellow­,Bl­ue,Red 
 >>> Blue

The special variable RS

By default, AWK treats each line of its input as a separate record. But what if the input line is not devided into lines ? Let take the file OneLin­e.txt as an example:
 
cat OneLin­e.txt 
 AWK,is­,aw­eso­me!­Let­,le­arn­,AW­K!H­ell­o,AWK
In this file, fields are separated by comma and records are separated by exclam­ation point. Let see the following code which print the second field of each record.
 
awk 'BEGIN {RS="!";­FS=­"­,"} {print $2}' OneLin­e.txt 
 >>> is 
 >>> learn 
 >>> AWK
 

OFS and ORS

AWK has also the output version of FS and RS which are respec­tively OFS and ORS. Let take an example using the file names.txt.
 
awk 'BEGIN {OFS=",­"­;OR­S="!­"} {print $1,$2}' names.txt 
 >>> Albert­,Ei­nst­ein­!Ba­rak­,Ob­ama­!St­eve­,Jobs!
Note that the setting of OFS has no effect on the output of $0.

The special variable NR

NR is a special variable whose value is the record number or line number of the record that is currently being examined .
 
awk '{print NR,$0}' awk.txt 
 >>> 1 AWK is awesome 
 >>> 2 Let learn AWK together 
 >>> 3 AWK is used for text processing
If we put two input files the result will be the concat­enation of the two files.

The special variable FNR

FNR is a special variable whose value is the record number of each file.
 
awk '{print FNR, $0}' names.txt awk.txt 
 >>> 1 Albert Einstein 
 >>> 2 Barak Obama 
 >>> 3 Steve Jobs 
 >>> 1 AWK is awesome 
 >>> 2 Let  learn AWK together 
 >>> 3 AWK is used for text processing
 

The special variable FILENAME

The special variable FILENAME print the name of a file.
 
awk '{print FILENA­ME,$0}' names.txt awk.txt 
 >>> names.txt Albert Einshtein 
 >>> names.txt Barak Obama 
 >>> names.txt Steve Jobs 
 >>> awk.txt AWK is awesome 
 >>> awk.txt Let learn AWK together 
 >>> awk.txt AWK is used for text processing