awk - KeynesYouDigIt/Knowledge GitHub Wiki

Basic Structure

pattern { action }

BEGIN pattern { action } { action } END pattern { action }

Print Options

• print - The action to print
• /t - Tab
• Invoke awk -F, to comma-separate

Regex

• word ~ /(first_word|second_word)/ - Matches
• word !~ /WORD/ - Doesn't match

Scripting

• ' nests
• exit - Early-exit the script

awk Syntax

#!/bin/awk -f
BEGIN { print "File\tOwner" } 
    { print $8, "\t", $3}   
END { print " - DONE -" } 

bash Syntax

    #!/bin/sh
    awk '{print $'$column'}'

Variables

• name="Kyle" - Assignment
• $0 is the whole line
• $1, $4, etc. - Gives you each column
• $name - Named variable
• Globals
  • You can use more than one character
  • NF - Number of fields
  • NR - Number of records, or the current record
  • ORS Record separator
  • FS - Column separator
  • FILENAME - Current filename
  • ARGV[1] - An array of arguments
  • ENVIRON["name"] - Array of variables

#!/bin/sh
column=${1:-1} # 1 is first variable passed in, -1 is default value
awk '{print $'$column'}'

Conditionals

#!/bin/awk

if (conditional){
} else if {
} else {
}

Loops

while ( conditional ) {
    next
}
for ( expression ; conditional ; expression ) {
    continue
}
for ( variable in array ) statement {
    break
}

Functions

• substr(string,position,length)
• split(string,array,separator)
• tolower(string)
• toupper(string)
• sub(/pattern/, replacement, string)
• match(string, pattern)
  • RSTART - Index of start
  • RLENGTH - Length of match
• system("unix_command") - Returns exit code
• function(parameter){}

No input processing

#!/bin/awk -f
# Doesn't process any text
BEGIN {
    print "File\tOwner"
    exit;
}

Notes

• You can't interpolate variables in actions