awk built in variables
| 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". |
Range Of Fields ‹↑›
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
Awk One Line Recipes ‹↑›
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
- www: http://www.pement.org/awk/awk1line.txt
-
Latest version of the Eric Pement one line scripts (in English)
- www: http://ximix.org/translation/awk1line_zh-CN.txt
-
Chinese version of these one line scripts
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"}'
Summing Numeric Columns ‹↑›
sum up all the numbers in column 2 and print out the total at the end
awk '{ a+=$2 } END { print "total=" a }' data.txt
sum 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}' | less
Line Numbering ‹↑›
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};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}' 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}'
The Number Of Fields ‹↑›
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'
String Creation ‹↑›
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'
Array Creation ‹↑›
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
Text Conversion And Substitution ‹↑›
IN UNIX ENVIRONMENT: convert DOS newlines (CR/LF) to Unix format
awk '{sub(/\r$/,"")};1' # assumes EACH line ends with Ctrl-M
IN UNIX ENVIRONMENT: convert Unix newlines (LF) to DOS format
awk '{sub(/$/,"\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
delete leading whitespace (spaces, tabs) from front of each line
awk '{sub(/^[ \t]+/, "")};1'
delete 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 fields
insert 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 line
substitute "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/passwd
Rearranging Fields Or Columns ‹↑›
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);print ""}' file
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 any line where field #5 is equal to "abc123"
awk '$5 == "abc123"'
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"'
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}'
awk '/regex/{print (NR==1 ? "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 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)
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 '/./'
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
Pipe Awk Output To The Shell ‹↑›
This 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"}' | sh
More One Line Examples ‹↑›
Print first two fields in opposite order
awk '{ print $2, $1 }' file
Print lines longer than 72 characters
awk 'length > 72' file
Print length of string in 2nd column
awk '{print length($2)}' file
Add 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 }' file
Print 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 }' file
Print column 3 if column 1 > column 2
awk '$1 > $2 {print $3}' file
Print 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++}' file
Print sequence number and then column 1 of file
awk '{print NR, $1}' file
Print every line after erasing the 2nd field
awk '{$2 = ""; print}' file
Print hi 28 times
yes | head -28 | awk '{ print "hi" }'
Print hi.0010 to hi.0099 (NOTE IRAF USERS!)
yes | head -90 | awk '{printf("hi00%2.0f \n", NR+9)}'
Print out 4 random numbers between 0 and 1
yes | head -4 | awk '{print rand()}'
Print out 40 random integers modulo 5
yes | head -40 | awk '{print int(100*rand()) % 5}'
Replace every field by its absolute value
{ for (i = 1; i <= NF; i=i+1) if ($i < 0) $i = -$i print}
Field Delimiter ‹↑›
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
awk -F\| '{print $4}' filename
awk 'BEGIN {FS="|"} {print $4}' filename
set the field delimiter to be a comma followed by a space, print 2nd field
awk -F', ' '{print $2}' data.txt
set 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
awk 'BEGIN{FS=", *";};{print $2;}' data.txt
set the field delimiter to be the double quote character
awk -F'"' '{print $2}' data.txt
awk -F\" '{print $2}' data.txt
set the field delimiter to be any number of '+' plus signs
awk -F'\+*' '{print $2}' data.txt
set the field delimiter to a space following by one or more '*' star signs
awk -F' \*+' '{print $2}' data.txt
Some 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
}
,,,
example format strings for 'printf'
| 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 |
Find maximum and minimum values present in column 1
NR == 1 {m=$1 ; p=$1}
$1 >= m {m = $1}
$1 <= p {p = $1}
END { print "Max = " m, " Min = " p }
,,,
Example of defining variables, multiple commands on one line
NR == 1 {prev=$4; preva = $1; prevb = $2; n=0; sum=0}
$4 != prev {print preva, prevb, prev, sum/n; n=0; sum=0; prev = $4; preva = $1;
prevb = $2}
$4 == prev {n++; sum=sum+$5/$6}
END {print preva, prevb, prev, sum/n}
,,,
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)
{ # 1 == Jan 1, 1901
split("31 28 31 30 31 30 31 31 30 31 30 31", days)
# 365 days a year, plus one for each leap year
n = (y-1901) * 365 + int((y-1901)/4)
if (y % 4 == 0) # leap year from 1901 to 2099
days[2]++
for (i = 1; i < m; i++)
n += days[i]
return n + d
}
{ print daynum($1, $2, $3) }
,,,
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)}
,,,
Password Generation With Awk ‹↑›
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 | less
as above but with all punctuation removed
awk '{gsub(/[[:punct:]]/,"");print last$0; last=$0}' /usr/share/dict/words | less
Software Written With Awk ‹↑›
http://www.soimort.org/translate-shell/
a very good command line script to access Google translate
Alternatives To Awk ‹↑›
awk is particularly good handling 'csv' (comma separated
values) data or other tabular style data.
cut -
perl -
sed -
Books About Awk ‹↑›
"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").
Awk Contributors ‹↑›
Peter S. Tillier (U.K.); Daniel Jana; Yisu Dong
History ‹↑›
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.dat
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