AWK

AWK is an extremely versatile programming language for working on files and is named after its three original authors:

• Alfred V. Aho
• Brian W. Kernighan
• Peter J. Weinberger

They write: Awk is a convenient and expressive programming language that can be applied to a wide variety of computing and data-manipulation tasks.

Introduction

The AWK scripting language is a powerful solution for handling text. It may not give a solution for any programming issue, but it sure is a handy and convenient.

Built-in Variables

Variable	Description	Default
ARGC	Number of command line arguments	-
ARGV	Array of command-line arguments	-
FILENAME	Name of the current input file	-
FNR	Record number in the current file	-
FS	Controls the input field separator	" " (space)
NF	Number of fields in the current record	-
NR	Number of records read so far	-
OFMT	Output format for numbers (as used in printf)	%.6g"
OFS	Output field separator	" " (space)
ORS	Output record separator	"\n"
RLENGHT	Length of the input record separator	-
RS	Controls the input record separator	\n
RSTART	Start of string matched by match function	-
SUBSEP	Subscript separator, also called FS in Ascii.	Oct: \034, Dec: 28, Hex: \0x1C

Most implementations of awk are interpreters which read your awk source program and parse it and act on it directly. Example implementations:

1. nawk, AT&T's `new awk' -- probably nobody uses the `old awk' anymore-- . Interpreter, might NOT be well-maintained
2. gawk, GNU project, interpreter.
3. mawk, Michael Brennan, interpreter.
4. tawk, Thompson Automation, interpreter, compiler, MS-Windows DLL
5. mksawk, Mortice Kern Systems (MKS), interpreter, compiler,

Examples

Command	Description
awk '{ print $2, $1 }' file	Print first two fields in opposite order.
awk 'length > 80' file	Print lines longer than 80 characters.
awk '{print length($2)}' file	Print length of string in 2nd column.
awk '{ for (i = NF; i > 0; --i) print $i }' file	Print fields in reverse order.
awk '/start/, /stop/' file	Prints all lines between start/stop pairs including 'start' and 'stop'.
awk '$1 != prev { print; prev = $1 }' file	Prints all lines whose first field is different from previous one.
awk '$1 > $2 {print $3}' file	Print column 3 of column 1 > column 2.
awk '$3 > $2' file	Prints line if column 3 > column 2.
awk '$3 > $1 {print i + "1"; i++}' file	Counts number of lines where column 3 > column 1
awk '{print NR, $1}' file	Prints sequence number and column 1 of file.
awk '{$2 = ""; print}' file	Prints every line after erasing the 2nd column.
head -28 | awk '{ print "hi" }'	Prints 'hi' 28 times.
head -4 | awk '{print rand()}'	Prints 4 random numbers between 0 and 1. Always the same sequences. Use srand() to prevent this.
awk '{printf("%15s %12s %3s %12s %12s %-s\n", $5, $1, $2, $3, $4, $9)}' | sort	Sorts a directory on size and show the result.
df -P / | grep /dev | awk '{print $5}' | sed 's/%//g'	Shows the free capacity (which is a percentage) of the root directory of a hard disk

Scripts	Description
{ s += $1 } END { print "sum is", s, " average is", s/NR }	Add up first column, print sum and average,
{line = $0} END {print line}	Prints the last line.
/Pattern/ {nlines = nlines + 1} END {print nlines}	Prints the total number of lines containing the word 'pattern'.

GAWK

The GAWK implementation is also available for windows.

• gnu gawk,
  • Savannah gnu, Sources of GAWK.
  • gnuwin, gawk packages and binaries.

See also

• Grymoire, Tutorial and introduction made by Bruce Barnet.
• GNU.org, The GNU Awk User’s Guide.
• pement.org, AWK one liners by Eric Pement
• IBM, AWK Tutorial Part 1.
• IBM, AWK Tutorial Part 2.