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# Basic usage
awk [options] '/<search_pattern>/ { <action_1>; <action_2>; }' <file>
# Either of the search pattern or the action can be omited.
# Default action is print, default pattern is every line.

awk '{print}' <file> # Print every line
awk '/spam/' <file> # Print lines containing `spam`
awk '/^spam/' <file> # Print lines starting with `spam`

awk '/^spam/ {print $1;}' <file> # Print only the first column ($1)
# $2 refers to the second column, $0 to the entire line

Built-in variables

awk built-in variables
  • FILENAME: Current input file.
  • NF: Number of fields in the current record.
  • NR: Number of the current record.
  • FNR: Number of the current record relative to the current input file.
  • FS: Current field separator (default: whitespace).
  • OFS: Field separator for the output (default: whitespace).
  • RS: Record separator for the input file (default: newline).
  • ORS: Record separator for the output (default: newline).
# Print the first column of `/etc/passwd`
# Change the field separator variable to `:` before processing
awk 'BEGIN { FS=":"; }
{ print $1; }' /etc/passwd

awk -F ':' '{print $1;}' /etc/passwd # Equivalent to above
awk -F: '{print $1;}' /etc/passwd # Equivalent to above

# Transform the data into a table
awk 'BEGIN { FS=":"; print "User\t\tUID\t\tGID\t\tHome\t\tShell\n--------------"; }
{print $1,"\t\t",$3,"\t\t",$4,"\t\t",$6,"\t\t",$7;}
END { print "---------\nFile Complete" }' /etc/passwd

Field searching

awk '$2 ~ /^bin/' <file> # Print lines where the second field starts with `bin`
awk '$2 !~ /^bin/' <file> # The second field does _not_ start with `bin`
awk '$2 !~ /^bin/ && $1 < 5' <file> # The second field does not start with `bin` _and_ the value of the first column is less than 5


awk -f script.awk <file> # Run script.awk on file