AWK one liners

UNIX Basics Examples with awk A short introduction

A colleague of mine used AWK to extract the first column from a file with the command:

awk '  '{print $1}'   file

Easy, isn't it? This simple task does not need complex programming in C. One line of AWK does it. Once we have learned the lesson on how to extract a column we can do things such as renaming files (append .new to "files_list"):

ls files_list | awk '{print "mv "$1" "$1".new"}' | sh

... and more:

1. Renaming within the name:
   ls -1 *old* | awk '{print "mv "$1" "$1}' | sed s/old/new/2 | sh
   (although in some cases it will fail, as in file_old_and_old)
2. Remove only files:
   ls -l * | grep -v drwx | awk '{print "rm "$9}' | sh
   or with awk alone:
   ls -l|awk '$1!~/^drwx/{print $9}'|xargs rm
   Be careful when trying this out in your home directory. We remove files!
3. Remove only directories
   ls -l | grep '^d' | awk '{print "rm -r "$9}' | sh
   or
   ls -p | grep /$ | wk '{print "rm -r "$1}'
   or with awk alone:
   ls -l|awk '$1~/^d.*x/{print $9}'|xargs rm -r
   Be careful when trying this out in your home directory. We remove things!
4. Killing processes by name (in this example we kill the process called netscape):
   kill `ps auxww | grep netscape | egrep -v grep | awk '{print $2}'`
   or with awk alone:
   ps auxww | awk '$0~/netscape/&&$0!~/awk/{print $2}' |xargs kill
   It has to be adjusted to fit the ps command on whatever unix system you are on. Basically it is: "If the process is called netscape and it is not called 'grep netscape' (or awk) then print the pid"

Recommended Links

The AWK Manual - One-liners  Useful "One-liners"

Useful awk programs are often short, just a line or two. Here is a collection of useful, short programs to get you started. Some of these programs contain constructs that haven't been covered yet. The description of the program will give you a good idea of what is going on, but please read the rest of the manual to become an awk expert!

awk '{ if (NF > max) max = NF }

     END { print max }'

This program prints the maximum number of fields on any input line.

awk 'length($0) > 80'

This program prints every line longer than 80 characters. The sole rule has a relational expression as its pattern, and has no action (so the default action, printing the record, is used).

awk 'NF > 0'

This program prints 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 '{ if (NF > 0) print }'

This program also prints every line that has at least one field. Here we allow the rule to match every line, then decide in the action whether to print.

awk 'BEGIN { for (i = 1; i <= 7; i++)

               print int(101 * rand()) }'

This program prints 7 random numbers from 0 to 100, inclusive.

ls -l files | awk '{ x += $4 } ; END { print "total bytes: " x }'

This program prints the total number of bytes used by files.

expand file | awk '{ if (x < length()) x = length() }

                  END { print "maximum line length is " x }'

This program prints the maximum line length of file. The input is piped through the expand program to change tabs into spaces, so the widths compared are actually the right-margin columns.

awk 'BEGIN { FS = ":" } { print $1 | "sort" }' /etc/passwd

This program prints a sorted list of the login names of all users.

awk '{ nlines++ }

     END { print nlines }'

This programs counts lines in a file.

awk 'END { print NR }'

This program also counts lines in a file, but lets awk do the work.

awk '{ print NR, $0 }'

This program adds line numbers to all its input files, similar to `cat -n'.

HANDY ONE-LINERS FOR AWK 22 July 2003 compiled by Eric Pement ...

HANDY ONE-LINERS FOR AWK                                  22 July 2003
compiled by Eric Pement <pemente@northpark.edu>           version 0.22
   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 <infile >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.

#---end of file---

AWK One-Liners

Although awk can be used to write programs of some complexity, many useful programs are not complicated. Here is a collection of short programs that you might find handy and/or instructive:

1. Print the total numnber of input lines:

   END { print NR }

2. Print the tenth input line:

   NR == 10

3. Print the last field of every input line:

   { print $NF }

4. Print the last field of the last input line:

   { field = $NF}
   END { print field } 

5. Print every input line with more than 4 fields:

   NF > 4

6. Print every input line in which the last field is more than 4:

   $NF > 4

7. Print the total number of fields in all input lines:

   { nf = nf + NF }
   END { print nf }      

8. Print the total number of lines that contain Beth:

   /Beth/ { nlines = nlines + 1 }
   END { print nlines }      

9. Print the largest first fields and the line that contains it ( assumes some $1 is positive):

   $1 > max { max = $1 ; maxlines = $0 }
   END { print max, maxline)
          

10. Print every line that has at least one field:

    NF > 0

11. Pritn every line longer than 80 characters:

    length($0) > 80

12. Print the numer of fields in every line, followed by the line itself:

    { print NF, $0 }

13. Print the first two fields, in opposite order, of every line:

    { print $2, $1 }

14. Exchange the first two fields of every line and then print the line:

    { temp = $1 ; $1 = $2 ; $2 = temp ; print }

15. Print every line witg rge first field replaced by the line number:

    { $1 = NR ; print }

16. Print every line after erasing the second field:

    { $2 = ""; print }

17. Print in reverse order the fields of every line:

    { for (i=NF ; i>0 ; i=i-1) printf( "%s ", $1)
           printf("\n")
    }       

18. Print the sums of the fields of every line:

    { sum = 0
           for ( i=1 ; i<=NF ; i=i+1) sum = sum + $i
           print sum
    }       

19. Ad up all fields in all lines and print the sum:

    { for ( i=1 ; i<=NF ; i=i+1 ) sum = sum + $i}
    END { print sum }       
           

20. Print every line after replacing each field by its absolute value:

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

Source: The AWK Programming Language

One-liners

Useful "One-liners"
*******************

   Useful `awk' programs are often short, just a line or two.  Here is a
collection of useful, short programs to get you started.  Some of these
programs contain constructs that haven't been covered yet.  The
description of the program will give you a good idea of what is going
on, but please read the rest of the manual to become an `awk' expert!

   Since you are reading this in Info, each line of the example code is
enclosed in quotes, to represent text that you would type literally.
The examples themselves represent shell commands that use single quotes
to keep the shell from interpreting the contents of the program.  When
reading the examples, focus on the text between the open and close
quotes.

`awk '{ if (NF > max) max = NF }'
`     END { print max }''
     This program prints the maximum number of fields on any input line.

`awk 'length($0) > 80''
     This program prints every line longer than 80 characters.  The sole
     rule has a relational expression as its pattern, and has no action
     (so the default action, printing the record, is used).

`awk 'NF > 0''
     This program prints 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 '{ if (NF > 0) print }''
     This program also prints every line that has at least one field.
     Here we allow the rule to match every line, then decide in the
     action whether to print.

`awk 'BEGIN { for (i = 1; i <= 7; i++)'
`               print int(101 * rand()) }''
     This program prints 7 random numbers from 0 to 100, inclusive.

`ls -l FILES | awk '{ x += $4 } ; END { print "total bytes: " x }''
     This program prints the total number of bytes used by FILES.

`expand FILE | awk '{ if (x < length()) x = length() }'
`                  END { print "maximum line length is " x }''
     This program prints the maximum line length of FILE.  The input is
     piped through the `expand' program to change tabs into spaces, so
     the widths compared are actually the right-margin columns.

`awk 'BEGIN { FS = ":" }'
`     { print $1 | "sort" }' /etc/passwd'
     This program prints a sorted list of the login names of all users.

`awk '{ nlines++ }'
`     END { print nlines }''
     This programs counts lines in a file.

`awk 'END { print NR }''
     This program also counts lines in a file, but lets `awk' do the
     work.

`awk '{ print NR, $0 }''
     This program adds line numbers to all its input files, similar to
     `cat -n'.
 

The GAWK Manual - Useful One-liners

Useful awk programs are often short, just a line or two. Here is a collection of useful, short programs to get you started. Some of these programs contain constructs that haven't been covered yet. The description of the program will give you a good idea of what is going on, but please read the rest of the manual to become an awk expert!

awk '{ if (NF > max) max = NF }

END { print max }'

This program prints the maximum number of fields on any input line.

awk 'length($0) > 80'

This program prints every line longer than 80 characters. The sole rule has a relational expression as its pattern, and has no action (so the default action, printing the record, is used).

awk 'NF > 0'

This program prints 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 '{ if (NF > 0) print }'

This program also prints every line that has at least one field. Here we allow the rule to match every line, then decide in the action whether to print.

awk 'BEGIN { for (i = 1; i <= 7; i++)

print int(101 * rand()) }'

This program prints 7 random numbers from 0 to 100, inclusive.

ls -l files | awk '{ x += $4 } ; END { print "total bytes: " x }'

This program prints the total number of bytes used by files.

expand file | awk '{ if (x < length()) x = length() }

END { print "maximum line length is " x }'

This program prints the maximum line length of file. The input is piped through the expand program to change tabs into spaces, so the widths compared are actually the right-margin columns.

awk 'BEGIN { FS = ":" }

{ print $1 | "sort" }' /etc/passwd

This program prints a sorted list of the login names of all users.

awk '{ nlines++ }

END { print nlines }'

This programs counts lines in a file.

awk 'END { print NR }'

This program also counts lines in a file, but lets awk do the work.

awk '{ print NR, $0 }'

This program adds line numbers to all its input files, similar to `cat -n'

Last modified: March 15, 2008