Getting Started

# => 5
awk 'BEGIN{print length("hello")}'
# => HELLO
awk 'BEGIN{print toupper("hello")}'
# => hel
awk 'BEGIN{print substr("hello", 1, 3)}'

See: Functions

awk 'BEGIN {
   fruits["mango"] = "yellow";
   fruits["orange"] = "orange"
   for(fruit in fruits) {
     print "The color of " fruit " is " fruits[fruit]
   }
}'

See: Arrays

awk 'BEGIN{
    while (a++ < 1000)
        s=s " ";
    print s
}'

See: Loops

awk -F: '$3>30 {print $1}' /etc/passwd

See: Conditions

awk 'BEGIN {print "hello world"}'        # Prints "hello world"
awk -F: '{print $1}' /etc/passwd         # -F: Specify field separator
# /pattern/ Execute actions only for matched pattern
awk -F: '/root/ {print $1}' /etc/passwd                     
# BEGIN block is executed once at the start
awk -F: 'BEGIN { print "uid"} { print $1 }' /etc/passwd     
# END block is executed once at the end
awk -F: '{print $1} END { print "-done-"}' /etc/passwd

          $1      $2/$(NF-1)    $3/$NF
           ▼          ▼           ▼ 
        ┌──────┬──────────────┬───────┐
$0/NR ▶ │  ID  │  WEBSITE     │  URI  │
        ├──────┼──────────────┼───────┤
$0/NR ▶ │  1   │  quickref.me │  awk  │
        ├──────┼──────────────┼───────┤
$0/NR ▶ │  2   │  google.com  │  25   │
        └──────┴──────────────┴───────┘

# First and last field
awk -F: '{print $1,$NF}' /etc/passwd
# With line number
awk -F: '{print NR, $0}' /etc/passwd
# Second last field
awk -F: '{print $(NF-1)}' /etc/passwd
# Custom string 
awk -F: '{print $1 "=" $6}' /etc/passwd

See: Variables

BEGIN          {<initializations>} 
   <pattern 1> {<program actions>} 
   <pattern 2> {<program actions>} 
   ...
END            {< final actions >}

#Example

awk '
    BEGIN { print "\n>>>Start" }
    !/(login|shutdown)/ { print NR, $0 }
    END { print "<<<END\n" }
' /etc/passwd

$ awk -F: '{print $1, $NF}' /etc/passwd