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WHAT'S NEW?

Mar 01: Michael Sanders demos an X-windows GUI for AWK.

Mar 01: Awk100#24: A. Lahm and E. de Rinaldis' patent search, in AWK

Feb 28: Tim Menzies asks this community to write an AWK cookbook.

Feb 28: Arnold Robbins announces a new debugger for GAWK.

Feb 28: Awk100#23: Premysl Janouch offers a IRC bot, In AWK

Feb 28: Updated: the AWK FAQ

Feb 28: Tim Menzies offers a tiny content management system, in Awk.

Jan 31: Comment system added to awk.info. For example, see discussion bottom of ?keys2awk

Jan 31: Martin Cohen shows that Gawk can handle massively long strings (300 million characters).

Jan 31: The AWK FAQ is being updated. For comments/ corrections/ extensions, please mail tim@menzies.us

Jan 31: Martin Cohen finds Awk on the Android platform.

Jan 31: Aleksey Cheusov released a new version of runawk.

Jan 31: Hirofumi Saito contributes a candidate Awk mascot.

Jan 31: Michael Sanders shows how to quickly build an AWK GUI for windows.

Jan 31: Hyung-Hwan Chung offers QSE, an embeddable Awk Interpreter.

[More ...]

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categories: OneLiners,Learn,Jan,2009,EricP

Handy One-Liners For Awk (v0.22)

Eric Pement
pemente@northpark.edu

Latest version of this file is usually at:
http://www.student.northpark.edu/pemente/awk/awk1line.txt

USAGE

Unix:     awk '/pattern/ {print "$1"}'    # standard Unix shells
DOS/Win:  awk '/pattern/ {print "$1"}'    # okay for DJGPP compiled
          awk "/pattern/ {print \"$1\"}"  # required for Mingw32

Most of my experience comes from version of GNU awk (gawk) compiled for Win32. Note in particular that DJGPP compilations permit the awk script to follow Unix quoting syntax '/like/ {"this"}'. However, the user must know that single quotes under DOS/Windows do not protect the redirection arrows (<, >) nor do they protect pipes (|). Both are special symbols for the DOS/CMD command shell and their special meaning is ignored only if they are placed within "double quotes." Likewise, DOS/Win users must remember that the percent sign (%) is used to mark DOS/Win environment variables, so it must be doubled (%%) to yield a single percent sign visible to awk.

If I am sure that a script will NOT need to be quoted in Unix, DOS, or CMD, then I normally omit the quote marks. If an example is peculiar to GNU awk, the command 'gawk' will be used. Please notify me if you find errors or new commands to add to this list (total length under 65 characters). I usually try to put the shortest script first.

File Spacing

Double space a file

 awk '1;{print ""}'
 awk 'BEGIN{ORS="\n\n"};1'

Double space a file which already has blank lines in it. Output file should contain no more than one blank line between lines of text. NOTE: On Unix systems, DOS lines which have only CRLF (\r\n) are often treated as non-blank, and thus 'NF' alone will return TRUE.

awk 'NF{print $0 "\n"}'

Triple space a file

awk '1;{print "\n"}'

Numbering and Calculations

Precede each line by its line number FOR THAT FILE (left alignment). Using a tab (\t) instead of space will preserve margins.

awk '{print FNR "\t" $0}' files*

Precede each line by its line number FOR ALL FILES TOGETHER, with tab.

awk '{print NR "\t" $0}' files*

Number each line of a file (number on left, right-aligned) Double the percent signs if typing from the DOS command prompt.

awk '{printf("%5d : %s\n", NR,$0)}'

Number each line of file, but only print numbers if line is not blank Remember caveats about Unix treatment of \r (mentioned above)

awk 'NF{$0=++a " :" $0};{print}'
 awk '{print (NF? ++a " :" :"") $0}'

Count lines (emulates "wc -l")

awk 'END{print NR}'

Print the sums of the fields of every line

awk '{s=0; for (i=1; i<=NF; i++) s=s+$i; print s}'

Add all fields in all lines and print the sum

awk '{for (i=1; i<=NF; i++) s=s+$i}; END{print s}'

Print every line after replacing each field with its absolute value

 awk '{for (i=1; i<=NF; i++) if ($i < 0) $i = -$i; print }'
 awk '{for (i=1; i<=NF; i++) $i = ($i < 0) ? -$i : $i; print }'

Print the total number of fields ("words") in all lines

 awk '{ total = total + NF }; END {print total}' file

Print the total number of lines that contain "Beth"

 awk '/Beth/{n++}; END {print n+0}' file

Print the largest first field and the line that contains it Intended for finding the longest string in field #1

awk '$1 > max {max=$1; maxline=$0}; END{ print max, maxline}'

Print the number of fields in each line, followed by the line

awk '{ print NF ":" $0 } '

Print the last field of each line

awk '{ print $NF }'

Print the last field of the last line

awk '{ field = $NF }; END{ print field }'

Print every line with more than 4 fields

awk 'NF > 4'

Print every line where the value of the last field is > 4

awk '$NF > 4'

Text Conversion and Substitution

IN UNIX ENVIRONMENT: convert DOS newlines (CR/LF) to Unix format

awk '{sub(/\r$/,"");print}'   # assumes EACH line ends with Ctrl-M

IN UNIX ENVIRONMENT: convert Unix newlines (LF) to DOS format

awk '{sub(/$/,"\r");print}

IN DOS ENVIRONMENT: convert Unix newlines (LF) to DOS format

awk 1

IN DOS ENVIRONMENT: convert DOS newlines (CR/LF) to Unix format Cannot be done with DOS versions of awk, other than gawk:

gawk -v BINMODE="w" '1' infile >outfile

Use "tr" instead.

 tr -d \r outfile # GNU tr version 1.22 or higher

Delete leading whitespace (spaces, tabs) from front of each line aligns all text flush left

awk '{sub(/^[ \t]+/, ""); print}'

Delete trailing whitespace (spaces, tabs) from end of each line

awk '{sub(/[ \t]+$/, "");print}'

Delete BOTH leading and trailing whitespace from each line

awk '{gsub(/^[ \t]+|[ \t]+$/,"");print}'
awk '{$1=$1;print}'           # also removes extra space between fields

Insert 5 blank spaces at beginning of each line (make page offset)

awk '{sub(/^/, "     ");print}'

Align all text flush right on a 79-column width

awk '{printf "%79s\n", $0}' file*

Center all text on a 79-character width

awk '{l=length();s=int((79-l)/2); printf "%"(s+l)"s\n",$0}' file*

Substitute (find and replace) "foo" with "bar" on each line

awk '{sub(/foo/,"bar");print}'           # replaces only 1st instance
gawk '{$0=gensub(/foo/,"bar",4);print}'  # replaces only 4th instance
awk '{gsub(/foo/,"bar");print}'          # replaces ALL instances in a line

Substitute "foo" with "bar" ONLY for lines which contain "baz"

awk '/baz/{gsub(/foo/, "bar")};{print}'

Substitute "foo" with "bar" EXCEPT for lines which contain "baz"

awk '!/baz/{gsub(/foo/, "bar")};{print}'

Change "scarlet" or "ruby" or "puce" to "red"

awk '{gsub(/scarlet|ruby|puce/, "red"); print}'

Reverse order of lines (emulates "tac")

awk '{a[i++]=$0} END {for (j=i-1; j>=0;) print a[j--] }' file*

If a line ends with a backslash, append the next line to it (fails if there are multiple lines ending with backslash...)

awk '/\\$/ {sub(/\\$/,""); getline t; print $0 t; next}; 1' file*

Print and sort the login names of all users

awk -F ":" '{ print $1 | "sort" }' /etc/passwd

Print the first 2 fields, in opposite order, of every line

awk '{print $2, $1}' file

Switch the first 2 fields of every line

awk '{temp = $1; $1 = $2; $2 = temp}' file

Print every line, deleting the second field of that line

awk '{ $2 = ""; print }'

Print in reverse order the fields of every line

awk '{for (i=NF; i>0; i--) printf("%s ",i);printf ("\n")}' file

Remove duplicate, consecutive lines (emulates "uniq")

awk 'a !~ $0; {a=$0}'

Remove duplicate, nonconsecutive lines

awk '! a[$0]++'                     # most concise script
awk '!($0 in a) {a[$0];print}'      # most efficient script

Concatenate every 5 lines of input, using a comma separator between fields

awk 'ORS=%NR%5?",":"\n"' file

Selective Printing of Certain Lines

Print first 10 lines of file (emulates behavior of "head")

awk 'NR < 11'

Print first line of file (emulates "head -1")

awk 'NR>1{exit};1'

Print the last 2 lines of a file (emulates "tail -2")

awk '{y=x "\n" $0; x=$0};END{print y}'

Print the last line of a file (emulates "tail -1")

awk 'END{print}'

Print only lines which match regular expression (emulates "grep")

awk '/regex/'

Print only lines which do NOT match regex (emulates "grep -v")

awk '!/regex/'

Print the line immediately before a regex, but not the line containing the regex

awk '/regex/{print x};{x=$0}'
 awk '/regex/{print (x=="" ? "match on line 1" : x)};{x=$0}'

Print the line immediately after a regex, but not the line containing the regex

awk '/regex/{getline;print}'

Grep for AAA and BBB and CCC (in any order)

awk '/AAA/; /BBB/; /CCC/'

Grep for AAA and BBB and CCC (in that order)

awk '/AAA.*BBB.*CCC/'

Print only lines of 65 characters or longer

awk 'length > 64'

Print only lines of less than 65 characters

awk 'length < 64'

Print section of file from regular expression to end of file

awk '/regex/,0'
awk '/regex/,EOF'

Print section of file based on line numbers (lines 8-12, inclusive)

awk 'NR==8,NR==12'

Print line number 52

awk 'NR==52'
awk 'NR==52 {print;exit}'          # more efficient on large files

Print section of file between two regular expressions (inclusive)

awk '/Iowa/,/Montana/'             # case sensitive

Selective Deletion of Certain Lines:

Delete ALL blank lines from a file (same as "grep '.' ")

awk NF
awk '/./'

Credits and Thanks

Special thanks to Peter S. Tillier for helping me with the first release of this FAQ file.

For additional syntax instructions, including the way to apply editing commands from a disk file instead of the command line, consult:

  • "sed & awk, 2nd Edition," by Dale Dougherty and Arnold Robbins O'Reilly, 1997
  • "UNIX Text Processing," by Dale Dougherty and Tim O'Reilly Hayden Books, 1987
  • "Effective awk Programming, 3rd Edition." by Arnold Robbins O'Reilly, 2001

To fully exploit the power of awk, one must understand "regular expressions." For detailed discussion of regular expressions, see

  • "Mastering Regular Expressions, 2d edition" by Jeffrey Friedl (O'Reilly, 2002).

The manual ("man") pages on Unix systems may be helpful (try "man awk", "man nawk", "man regexp", or the section on regular expressions in "man ed"), but man pages are notoriously difficult. They are not written to teach awk use or regexps to first-time users, but as a reference text for those already acquainted with these tools.

USE OF '\t' IN awk SCRIPTS: For clarity in documentation, we have used the expression '\t' to indicate a tab character (0x09) in the scripts. All versions of awk, even the UNIX System 7 version should recognize the '\t' abbreviation.

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