Awk

Basics

awk -F"," -v VAR=<value> '{<code}'

In awk: Use "," as field-separator, set VAR to <value> in.

awk '{ for(i = 1; i <= NF; i++) { print $i; } }'

Iterate over all fields

Standard variables

• NF Number of fields on the line
• FS The field seperator (default is whitespace)
• $0 The entire line
• $1 First field in line

a=length(field)

Get the length of a field.

String manipulation

substr(<string>,<start>,<num>)

From <sting> return <num> characters, starting from <start>

n=split(var,ARR,<fs>)

Split var in array ARR, n holds the number of elements in ARR, <fs> is the field separator, if not given the variable FS is used as field separator (default white space).

Default action of awk for read line is:

NF=split(var,ARR," ")
NR++
$0=var
for ( i=1 ; i<=NF ; i++ ) {
 $i=ARR[i]
}

gsub(<regexp>,<string>,<variable>)

Replace <regexp> with <string> in <variable>. Return number of replacements.

<variable> is modified.

printf "%-10s %05d\n", $1, $2

Format output like in Python:Strings#Advanced

Calculations

Print average of field 4 for all records in <file> containing 'GW'

awk 'BEGIN {}
/GW/ {GW+=$4}
END {print GW/NR}' <file>

Matching

/<pattern>/ {code}

Execute code if the current line matches <pattern>

var ~ /<pattern>/ {code}

Execute code if var matches <pattern>

!~ to negate the match

Magic

gawk '{if (NR%3 == 0) {print p$0;p=""}else{p=p$0}}'

Combine lines per 3 (Basic code found on stackoverflow [1])