Awk Cheatsheet

awk <command> <file1> <file2> ... <filen>

• code is enclosed in {}
• code in {} can be separated with ;
• command is enclosed in ''
• run from an awk file: -f progfile
• built-in function https://www.gnu.org/software/gawk/manual/htmlnode/Built002din.html#Built_002din

Printing fields by delimiter

• print the first field of each line, delimited by , awk -F',' '{print $1}' filename

Choosing the output delimiter

awk -F"," -v OFS=";" '{print $2}' filename

Match by regex

• simple match awk '/J/ {print}' filename

• match only field against regex (compared to whole line above) awk -F"," '$1 ~ /J/ {print}' filename // or !~ for not matching

Boolean condition

• Prints where snd field in line is > 200 awk -F"," '$2>200 {print $0}' filename

• Multiple conditions can be && || !

BEGIN and END

awk 'BEGIN { print "before first line" } { print $0 } END { print "After last line" }' filename

• Using begin and end with variables (total file size of all files > 200kb) ls -l | awk 'BEGIN {sum=0} $5>200 {sum+=$5} END{print sum}'

Useful commands

{ print $0; }  # prints $0. In this case, equivalent to 'print' alone
{ exit; }      # ends the program
{ next; }      # skips to the next line of input
{ a=$1; b=$0 } # variable assignment
{ c[$1] = $2 } # variable assignment (array)

{ if (BOOLEAN) { ACTION }
  else if (BOOLEAN) { ACTION }
  else { ACTION }
}
{ for (i=1; i<x; i++) { ACTION } }
{ for (item in c) { ACTION } }

Script template

BEGIN { # Can be modified by the user
  FS = ",";   # Field Separator
  RS = "\n";  # Record Separator (lines)
  OFS = " ";  # Output Field Separator
  ORS = "\n"; # Output Record Separator (lines)

  # Set variables
  Var = 22;
  print "Running the script"
}

/J/ && Var == 22 {printArg($1)}

END {
  print "Done with script"
}

function printArg(arg) { print arg; }