Awk Quick Start | Young's Blog

This article is a quick start for beginner. The common usage is as following:

awk <Action> <File Name>

awk will use space and tab to split every line into multiple setions using $1,$2 to represent.

Variable

we use $+Number variable to represent the sections of a line. The normal variable is as following:
NF: the number of the sections in current line.
$NF: the last section of current line
$(NF-1): the last two section of current line

Built-in variable

• FILENAME File name
• FS Field spilitor
• RS Row spilitor
• OPS Output spilitor
• ORS Output record spilitor
• OFMT Ouput format of numbers

Built-in function

• tolower()
• toupper()
• length()
• substr()
• sin()
• cos()
• sqrt()
• rand()
• …

Condition

Condition is for juding the output. The normal format is as following:
awk '<condition> <action>' <FileName>

awk -F ':' '/usr/' demo.txt
awk -F ':' 'NR %2 ==1 {print $1}' demo.txt

IF expression

IF expression is a kind of condition. The example is as following:

awk -F ':' '{if ($1 >"m") print $1}' demo.txt
awk -F ':' '{if ($1 >"m") print $1; else print "==="}' demo.txt

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