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Awk is a unix tool, or programming language designed to process and transform text files which are arranged in a series of 'fields' (chunks of text separated by spaces, or any other delimiter) and records. This document is mainly about the 'mawk' variant of 'awk'.
find out the version of mawk
mawk -W version
[+] The so-called "gotchas" are small but potentially frustating problems which arise and which stop a program from working or which make the awk program work in an unexpected way. Gotcha derives from the contraction of the english phrase "got you".
00- On a unix system the awk phrase <<awk "{print $1}">> doesnt work as expected because the unix (bash) shell expands or "interpolates" the "$1" variable. It is necessary to write "awk '{print $1}'" -
BEGIN and and variables such as FS must be uppercase
begin{FS=","}{print $2} No!! this doesnt worksimple usage of awk on different operating systems.
Unix: awk '/pattern/ {print "$1"}' # standard Unix shells
DOS/Win: awk '/pattern/ {print "$1"}' # compiled with DJGPP, Cygwin
awk "/pattern/ {print \"$1\"}" # GnuWin32, UnxUtils, Mingw
Users of MS-DOS or Microsoft Windows must remember that the percent sign (%) is used to indicate environment variables, so this symbol must be doubled (%%) to yield a single percent sign visible to awk.
run an awk script
cat file1 | awk -f a.awk > file2
awk -f a.awk file1 > file2 the same
Concatenation is the fancy term for joining 2 strings (bits of text) together.
print the first two columns of the space/tab delimited file 'data.txt'
awk '{print $1 $2}' data.txt $1 and $2 are printed with no space between awk '{print $1$2}' data.txt the same, at least on my mawk version awk '{print $1 $2;}' data.txt the same again awk '{print $1 "" $2}' data.txt the same again, but why would you?awk doesnt have variable 'interpolation' in strings
awk '{print "$1 ..."}' data.txt this prints '$1 ...' literallyprint the first column of 'data.txt' with 3 dots '...' appended to it
awk '{print $1 "..."}' data.txtappend a string to itself (string concatenation)
s = s "xxx"; this appends 3 x's to the end of the string 's'
determine if the variable "s" contains the letter "r"
s ~ /r/
print the first field of each line if it does *not* contain "a" or "b"
$1 !~ /(a|b)/ { print $1 } $1 !~ /[ab]/ { print $1 } the sameadd an "X" between every letter of every line
{ gsub(//, "X") ; print }split the string "s" into the array A using the pattern "r"
split(s, A, r)
make a multiline string..
print "\
<html> \n\
<head> \n\
"
print multiple expressions
print "variable a is " a "."
Its not possible to break printing expressions across lines
print "variable a is"
a ".";
this doesnt work, at least not with mawk 1.3.3display the file 'days.txt' with all newline characters removed
awk '{ printf "%s", $0 }' days.txt cat days.txt | awk '{ printf "%s", $0 }' the samedisplay 'days.txt' with newline characters replaced with spaces
awk '{ printf "%s ", $0 }' days.txt cat days.txt | awk '{ printf "%s ", $0 }'delete an array called record
delete record
assign a value to an associative style array
a["cars"] = 3
regular expression meta-characters: ^ $ . [ ] | ( ) * + ?
print all lines which start with an awk identifier
BEGIN { identifier = "[_a-zA-Z][_a-zA-Z0-9]*" }
$0 ~ "^" identifier
use tolower
tolower($0) ~ /bhp/ {print $0}set the ignorecase var
BEGIN {IGNORECASE=1} /bhp/ {print $0}loop through each field of each record
awk '{ for(i = 1 ; i <= NF ; i++) print $i }' /usr/share/dict/wordsprint each element of an array
for ( i in aa ) print aa[i]
# The field separator variable FS is interpreted as a regular # expression
split fields with any character followed by a colon ":" character
BEGIN {FS=".:"}split quoted comma delimited fields (csv)
BEGIN {FS="\" *, *\""}
| man gawk - the gnu awk man page |
| man ed - contains regular expression examples |
| man mawk - contains good examples |
| man regex - regular expression syntax |
Awk has no simple way to print a range of fields such as $[1-4] A 'for' loop must be used to loop through the range and print each one. One may use cut instead
use 'cut' to print fields 1 to 5 from a comma delimited file
cut -d, -f1-5
These one line scripts were taken from http://www.pement.org/awk/awk1line.txt
30 April 2008, by Eric Pement - eric [at] pement.org, version 0.27
double space a file
awk '1;{print ""}' awk 'BEGIN{ORS="\n\n"};1' another waydouble 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"}'sum up all the numbers in column 2 and print out the total at the end
awk '{ a+=$2 } END { print "total=" a }' data.txtsum a column between 2 lines in a file (with help from sed)
sed -n '/#1/,/#2/p' data.txt | awk -F, '{a+=$2; print $2, a}' | lessprecede 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};1' 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}' fileprint the total number of lines that contain "Beth"
awk '/Beth/{n++}; END {print n+0}' fileprint 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'
create a string of a specific length (e.g., generate 513 spaces)
awk 'BEGIN{while (a++<513) s=s " "; print s}'insert a string of specific length at a certain character position Example: insert 49 spaces after column #6 of each input line. gawk --re-interval 'BEGIN{while(a++<49)s=s " "};{sub(/^.{6}/,"&" s)};1'
These next 2 entries are not one-line scripts, but the technique is so handy that it merits inclusion here.
create an array named "month", indexed by numbers, so that month[1] is 'Jan', month[2] is 'Feb', month[3] is 'Mar' and so on.
split("Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec", month, " ")create an array named "mdigit", indexed by strings, so that mdigit["Jan"] is 1, mdigit["Feb"] is 2, etc. Requires "month" array
for (i=1; i<=12; i++) mdigit[month[i]] = i
IN UNIX ENVIRONMENT: convert DOS newlines (CR/LF) to Unix format
awk '{sub(/\r$/,"")};1' # assumes EACH line ends with Ctrl-MIN UNIX ENVIRONMENT: convert Unix newlines (LF) to DOS format
awk '{sub(/$/,"\r")};1'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
awk '{sub(/^[ \t]+/, "")};1' aligns all text flush leftdelete trailing whitespace (spaces, tabs) from end of each line
awk '{sub(/[ \t]+$/, "")};1'delete BOTH leading and trailing whitespace from each line
awk '{gsub(/^[ \t]+|[ \t]+$/,"")};1' awk '{$1=$1};1' # also removes extra space between fieldsinsert 5 blank spaces at beginning of each line (make page offset)
awk '{sub(/^/, " ")};1'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")}; 1' # replace only 1st instance gawk '{$0=gensub(/foo/,"bar",4)}; 1' # replace only 4th instance awk '{gsub(/foo/,"bar")}; 1' # replace ALL instances in a linesubstitute "foo" with "bar" ONLY for lines which contain "baz"
awk '/baz/{gsub(/foo/, "bar")}; 1'substitute "foo" with "bar" EXCEPT for lines which contain "baz"
awk '!/baz/{gsub(/foo/, "bar")}; 1'change "scarlet" or "ruby" or "puce" to "red"
awk '{gsub(/scarlet|ruby|puce/, "red")}; 1'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/passwdprint the first 2 fields, in opposite order, of every line
awk '{print $2, $1}' fileswitch the first 2 fields of every line
awk '{temp = $1; $1 = $2; $2 = temp}' fileprint 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);print ""}' fileconcatenate every 5 lines of input, using a comma separator between fields
awk 'ORS=NR%5?",":"\n"' file
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 any line where field #5 is equal to "abc123"
| ARGC - number of command line arguments. | |
| ARGV - array of command line arguments | 0..ARGC-1. |
| CONVFMT - format for conversion of numbers to string | default "%.6g". |
| ENVIRON - array indexed by environment variables. An environment string | var=value is stored as ENVIRON[var] = value. |
| FILENAME - name of the current input file. | |
| FNR - current record number in FILENAME. | |
| FS - splits records into fields as a regular expression. | |
| NF - number of fields in the current record. | |
| NR - current record number in the total input stream. | |
| OFMT - format for printing numbers; initially = "%.6g". | |
| OFS - inserted between fields on output | initially = " ". |
| ORS - terminates each record on output | initially = "\n". |
| RLENGTH - length set by the last call to the built-in function | match(). |
| RS - input record separator | initially = "\n". |
| RSTART - index set by the last call to match(). | |
| SUBSEP - used to build multiple array subscripts | initially = "\034". |
print only those lines where field #5 is NOT equal to "abc123" This will also print lines which have less than 5 fields.
awk '$5 != "abc123"'
matching a field against a regular expression
awk '$7 ~ /^[a-f]/' # print line if field #7 matches regex
awk '$7 !~ /^[a-f]/' # print line if field #7 does NOT match regex
print the line immediately before a regex, but not the line containing the regex
awk '/regex/{print 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 on the same line)
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)
print line number 52
print section of file between two regular expressions (inclusive)
awk '/Iowa/,/Montana/' # case sensitive
delete ALL blank lines from a file (same as "grep '.' ")
awk NF
awk '/./'
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 scriptThis technique allows each line generated by an awk script to be executed by the shell
move files to the "iraf" folder and add .dat to the names
ls junk* | awk '{print "mv "$0" ../iraf/"$0".dat"}' | shPrint first two fields in opposite order
awk '{ print $2, $1 }' filePrint lines longer than 72 characters
awk 'length > 72' file
Print length of string in 2nd column
awk '{print length($2)}' fileAdd up first column, print sum and average
{ s += $1 } END { print "sum is", s, " average is", s/NR }Print fields in reverse order
awk '{ for (i = NF; i > 0; --i) print $i }' filePrint the last line
{line = $0} END {print line}Print the total number of lines that contain the word Pat
/Pat/ {nlines = nlines + 1} END {print nlines}Print all lines between start/stop pairs
awk '/start/, /stop/' file
Print all lines whose first field is different from previous one
awk '$1 != prev { print; prev = $1 }' filePrint column 3 if column 1 > column 2
awk '$1 > $2 {print $3}' filePrint line if column 3 > column 2
awk '$3 > $2' file
Count number of lines where col 3 > col 1
awk '$3 > $1 {print i + "1"; i++}' filePrint sequence number and then column 1 of file
awk '{print NR, $1}' filePrint every line after erasing the 2nd field
awk '{$2 = ""; print}' filePrint hi 28 times
yes | head -28 | awk '{ print "hi" }'Print hi.0010 to hi.0099 (NOTE IRAF USERS!)
yes | head -90 | awk '{printf("hi00%2.0f \n", NR+9)}'Print out 4 random numbers between 0 and 1
yes | head -4 | awk '{print rand()}'Print out 40 random integers modulo 5
yes | head -40 | awk '{print int(100*rand()) % 5}'Replace every field by its absolute value
{ for (i = 1; i <= NF; i=i+1) if ($i < 0) $i = -$i print}The field delimiter or separator, determines how awk divides up each line of the text file into 'fields' or 'columns' which can then be accessed with the $1, $2, ... variables. The delimiter can be a regular expression (unlike 'cut' for example)
The default awk field delimiter is a single space " " or a tab.
use '|' as the field delimiter and print the 4th field
awk -F"|" '{print $4}' filename awk -F'|' '{print $4}' filename the same awk -F\| '{print $4}' filename should work awk 'BEGIN {FS="|"} {print $4}' filename the sameset the field delimiter to be a comma followed by a space, print 2nd field
awk -F', ' '{print $2}' data.txtset the field delimiter to be a comma followed by any number of spaces
awk -F', *' '{print $2}' data.txt awk 'BEGIN{FS=", *"}{print $2}' data.txt the same awk 'BEGIN{FS=", *";};{print $2;}' data.txt the same againset the field delimiter to be the double quote character
awk -F'"' '{print $2}' data.txt awk -F\" '{print $2}' data.txt the sameset the field delimiter to be any number of '+' plus signs
awk -F'\+*' '{print $2}' data.txtset the field delimiter to a space following by one or more '*' star signs
awk -F' \*+' '{print $2}' data.txtSome looping commands Remove a bunch of print jobs from the queue
BEGIN{ for (i=875;i>833;i--){ printf "lprm -Plw %d\n", i } exit } ,,,
Find maximum and minimum values present in column 1
| e.g. printf("howdy %-8s What it is bro. %.2f\n" | $1, $2*$3) |
| %s - string | |
| %-8s - 8 character string left justified | |
| %.2f - number with 2 places after . | |
| %6.2f - field 6 chars with 2 chars after . | |
| \n - newline | |
| \t - tab |
Example of defining variables, multiple commands on one line
Example of defining and using a function, inserting values into an array and doing integer arithmetic mod(n). This script finds the number of days elapsed since Jan 1, 1901. (from http://www.netlib.org/research/awkbookcode/c
h3) function daynum(y, m, d, days, i, n)
Example of using substrings substr($2,9,7) picks out characters 9 thru 15 of column 2
{print "imarith", substr($2,1,7) " - " $3, "out."substr($2,5,3)} {print "imarith", substr($2,9,7) " - " $3, "out."substr($2,13,3)} {print "imarith", substr($2,17,7) " - " $3, "out."substr($2,21,3)} {print "imarith", substr($2,25,7) " - " $3, "out."substr($2,29,3)} ,,,
A useful capability of awk may be in the generation of password 'dictionary' files, for the use with security auditing programs ('password crackers') such as "john" and "aircrack-ng". Awk may be used to amplify and multiplex a text password dictionary file.
print each line joining to the preceding line
awk '{print last$0; last=$0}' /usr/share/dict/words | lessas above but with all punctuation removed
awk '{gsub(/[[:punct:]]/,"");print last$0; last=$0}' /usr/share/dict/words | lesshttp://www.soimort.org/translate-shell/ a very good command line script to access Google translate
awk is particularly good handling 'csv' (comma separated values) data or other tabular style data.
cut - perl - sed -
"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)
"GAWK: Effective awk Programming," 3d edition, by Arnold D. Robbins (O'Reilly, 2003) or at http://www.gnu.org/software/gawk/manual/
"Mastering Regular Expressions, 3d edition" by Jeffrey Friedl (O'Reilly, 2006).
The info and manual ("man") pages on Unix systems may be helpful (try "man awk", "man nawk", "man gawk", "man regexp", or the section on regular expressions in "man ed").
Peter S. Tillier (U.K.); Daniel Jana; Yisu Dong
Awk was created by Aho, W? and Kernighan. Mr Aho has written some dense books about computer science. Brian Kernighan has been an important figure in the early development of Unix. Kernighan co-authored the first 'c' book- the C programming language, he also has maintained nroff (used for man pages) as well as other obscure unix tools.
Convert numbers to SI notation
$ awk '{ split(sprintf("%1.3e", $1), b, "e"); p = substr("yzafpnum_kMGTPEZY", (b[2]/3)+9, 1); o = sprintf("%f", b[1] * (10 ^ (b[2]%3))); gsub(/\./, p, o); print substr( gensub(/_[[:digit:]]*/, "", "g", o), 1, 4); }' < test.datDOCUMENT-NOTES: