Find and Replace text, database sort/validate/index.
Syntax
awk <options> 'Program' Input-File1 Input-File2 ...
awk -f PROGRAM-FILE <options> Input-File1 Input-File2 ...
Key
-F FS
--field-separator FS
Use FS for the input field separator (the value of the 'FS' predefined variable).
-f PROGRAM-FILE
--file PROGRAM-FILE
Read the awk program source from the file PROGRAM-FILE, instead of from the first
command line argument.
-mf NNN
-mr NNN
The 'f' flag sets the maximum number of fields, and the 'r' flag sets the maximum
record size. These options are ignored by 'gawk', since 'gawk' has no predefined limits;
they are only for compatibility with the Bell Labs research version of Unix awk.
-v VAR=VAL
--assign VAR=VAL
Assign the variable VAR the value VAL before program execution begins.
-W traditional
-W compat
--traditional
--compat
Use compatibility mode, in which 'gawk' extensions are turned off.
-W lint
--lint
Give warnings about dubious or non-portable awk constructs.
-W lint-old
--lint-old
Warn about constructs that are not available in the original V.7 Unix version of awk.
-W posix
--posix
Use POSIX compatibility mode, 'gawk' extensions are turned off and additional restrictions apply.
-W re-interval
--re-interval
Allow interval expressions, in regexps.
-W source=PROGRAM-TEXT
--source PROGRAM-TEXT
Use PROGRAM-TEXT as awk program source code.
This option allows mixing command line source code with source code from files, and is
particularly useful for mixing command line programs with library functions.
--
Signal the end of options. This is useful to allow further arguments to the awk program
itself to start with a '-'. This is mainly for consistency with POSIX argument parsing conventions.
'Program'
A series of patterns and actions: see below
Input-File
If no Input-File is specified then awk applies the Program to "standard input",
(piped output of some other command or the terminal.
Typed input will continue until end-of-file (typing 'Control-d')
The basic function of awk is to search files for lines (or other units of text) that contain a pattern.
When a line matches, awk performs a specific action on that line.
Suppose we have a file in which each line is a name followed by a phone number. Let’s say the file contains the line "Audrey 5550164."
In AWK, the first field is referred to as $1, the second as $2 and so on.
So an AWK program to retrieve Audrey’s phone number is:
awk '$1 == "Audrey" {print $2}' numbers.txt
which means if the first field matches Audrey, then print the second field.
In awk, $0 is the whole line of arguments.
The Program statement that tells awk what to do; consists of a series of "rules".
Each rule specifies one pattern to search for, and one action to perform when that pattern is found.
For ease of reading, each line in an awk program is normally a separate Program statement , like this:
pattern { action }
pattern { action }
...
e.g. Display lines from samplefile containing the string "123" or "abc" or "some text":
awk '/123/ { print $0 }
/abc/ { print $0 }
/some text/ { print $0 }' samplefile
A regular expression enclosed in slashes (/) is an awk pattern that matches every input record whose text belongs to that set. e.g. the pattern /foo/ matches any input record containing the three characters 'foo', *anywhere* in the record.
awk patterns can be one of the following:
/Regular Expression/ - Match = Pattern && Pattern - AND Pattern || Pattern - OR ! Pattern - NOT Pattern ? Pattern : Pattern - If, Then, Else Pattern1, Pattern2 - Range Start - end BEGIN - Perform action BEFORE input file is read END - Perform action AFTER input file is read
The special patterns BEGIN and END can be used to capture control before the first input line is read and after the last. BEGIN and END do not combine with other patterns.
Variable names with special meanings:
CONVFMT conversion format used when converting numbers
(default %.6g)
FS regular expression used to separate fields; also
settable by option -Ffs.
NF number of fields in the current record
NR ordinal number of the current record
FNR ordinal number of the current record in the current
file
FILENAME the name of the current input file
RS input record separator (default newline)
OFS output field separator (default blank)
ORS output record separator (default newline)
OFMT output format for numbers (default %.6g)
SUBSEP separates multiple subscripts (default 034)
ARGC argument count, assignable
ARGV argument array, assignable; non-null members are
taken as filenames
ENVIRON array of environment variables; subscripts are
names.
In addition to simple pattern matching awk has a huge range of text and arithmetic Functions, Variables and Operators.
'gawk' will ignore newlines after any of the following:
, { ? : || && do else
Comments - start with a '#', and continue to the end of the line:
# This program prints a nice friendly message
The AWK language was named after its authors, Al Aho, Peter Weinberger and Brian Kernighan.
From an ls - l listing, return the fifth item ($5) from each line of the output:
$ ls -l | awk '{print $5}'
Print the Row Number (NR), then a dash and space ("- ") and then the first item ($1) from each line in samplefile.txt:
$ awk '{print NR "- " $1 }' samplefile.txt
Print the first item ($1) and then the third last item $(NF-2) from each line in samplefile.txt:
$ awk '{print $1, $(NF-2) }' samplefile.txt
Print every line that has at least one field. This is an easy way to delete blank lines from a file (or rather, to
create a new file similar to the old file but from which the blank lines have been deleted)
awk 'NF > 0' data.txt
Comparison with grep:
Running grep Dec against the following file listing would return the 3 rows shown in bold as it matches text in different places:
-rw-r--r-- 7 simon simon 12043 Jan 31 09:36 December.pdf
-rw-r--r-- 3 simon simon 1024 Dec 01 11:59 README
-rw-r--r-- 3 simon simon 5096 Nov 14 18:22 Decision.txtRunning awk '$6 == "Dec"'against the same file listing, the relational operator $6 matches the exact field (column 6 = Month) so it will list only the December file:
$ ls -l /tmp/demo | awk '$6 == "Dec"'
Print the length of the longest input line:
awk '{ if (length($0) > max) max = length($0) }
END { print max }' data
Print seven random numbers from zero to 100, inclusive:
awk 'BEGIN { for (i = 1; i <= 7; i ) print int(101 * rand()) }'
Print the total number of bytes used by FILES:
ls -lg FILES | awk '{ x = $5 } ; END { print "total bytes: " x }'
Print the average file size of all .PNG files within a directory:
ls -l *.png | gawk '{sum = $5; n ;} END {print sum/n;}'
Print a sorted list of the login names of all users:
awk -F: '{ print $1 }' /etc/passwd | sort
Count the lines in a file:
awk 'END { print NR }' data
Print the even numbered lines in the data file:
awk 'NR % 2 == 0' data
If you were to use the expression 'NR % 2 == 1' instead, it would print the odd numbered lines.
“When the Last of the Great Auks Died, It Was by the Crush of a Fisherman’s Boot” ~ Samantha Galasso (Smithsonian)
AWK Help page - Brian Kernighan.
Why you should learn just a little Awk - Gregable.
Multiversity - Tutorial aimed at beginners.
AWK tutorial and introduction - Bruce Barnett.
Learn By Example - AWK text processing.
GNU Awk User Guide - Full guide with examples.
Book: The Awk Programming Language(pdf) 1988, Archive.org by Aho, Kernighan, and Weinberger
awk one liners - Eric Pement.
awk one liners explained & pt2 - Peteris Krumin (CatOnMat.net)
Patrick Hartigan - How to use awk.
awk, 'oawk', and 'nawk' - Alternative, older and newer versions of awk.
egrep - egrep foo FILES ...is essentially the same as awk '/foo/' FILES ...
expr - Evaluate expressions.
eval - Evaluate several commands/arguments.
for - Expand words, and execute commands
grep - Search file(s) for lines that match a given pattern.
m4 - Macro processor.
tr - Translate, squeeze, and/or delete characters.
Equivalent Windows command:
FOR - Conditionally perform a command several times.