Both pattern and procedure are optional If no pattern then all lines are processed If no procedure then matched lines are printed pattern can be: regular expression # For instance see relational expression # For instance NR == 9 pattern-matching expression # range: expression,expresion # For instance BEGIN END Except for BEGIN and END, patterns ca be combined with the boolean operators || && ! Range of lines can be expressed using comma: pattern1,pattern2 expressions can be composed of quoted strings numbers operators function calls user-defined variables built-in variables

$0 # Entire line $1 # First field $2 # Second field

ARGC The number of command line arguments (does not include options to awk, the program source or defined variables). ARGIND Current index into the ARGV array, and therefore ARGV[ARGIND] is always the current filename (FILENAME = ARGV[ARGIND] is always true. It can be modified, allowing you to skip over files. ARGV Array containing the list of arguments (or files) passed as command line arguments. CONVFMT Used to specify the format when converting a number to a string. The default value is "%.6g." ENVIRON Array containing the environment variables. ERRNO Describes the error, as a string, after a call to the getline command fails. FIELDWIDTHS Used when processing fixed width input. If you wanted to read a file that had 3 columns of data; the first one is 5 characters wide, the second 4, and the third 7: BEGIN {FIELDWIDTHS"5 4 7";} { printf("The three fields are %s %s %s\n", $1, $2, $3);} FILENAME Input filename (- for stdin) FNR Input record number. It is reset for each file read. The NR variable accumulates for all files read. FS Input line field separator IGNORECASE Its value is normally zero. When set to non-zero, all pattern matches ignore case. NF Number of fields of current record NR Number of records so far OFMT Output format for numbers OFS Output field separator ORS Output record separator RS Record separator RT Record terminator RSTART After the match() function is called, contains the location in the string of the search pattern. RLENGTH After the match() function is called, contains the length of this match. SUBSEP Multi-dimensional array separator

• # Addition/Positive
• # Subtraction/Negative

∗ # Multiplication / # Division % # Modulo ++ # Autoincrement – # Autodecrement

+= # Add result to variable -= # Subtract result from variable *= # Multiply variable by result /= # Divide variable by result %= # Apply modulo to variable

= # Is equal to ! # Is not equal to > # Is greater than >= # Is greater than or equal to < # Is less than <= # Is less than or equal to

&& # And

# Or

! # Not

<space> # Concatenation

~ # Matches !~ # Doesn't match

function name (arguments) { body }

#+BEGIN_SRC

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

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

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

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

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

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

awk 'NF{$0=++a " :" $0};1' awk '{print (NF? ++a " :" :"") $0}'

awk 'END{print NR}'

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

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

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 }'

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

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

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

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

awk '{ print $NF }'

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

awk 'NF > 4'

awk '$NF > 4' #+END_SRC

# 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-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            # 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]+/, "")};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

# 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

# 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

# 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

1. Display only the first three columns of the file SOMEFILE, using tabs to separate the results: awk '{print $1 "\t\t" $2 "\t" $3}' SOMEFILE
2. Display the first and fifth columns of the password file with a tab between them awk -F: '{print $1 "\t" $5}' /etc/passwd -F: changes the column delimiter from spaces (the default) to a colon (:)
3. Display the second column of the file using double colons as the field separator awk -v 'FS=::' '{print $2}' ratings.dat
4. replace first column as "ORACLE" in SOMEFILE awk '{$1 = "ORACLE"; print }' SOMEFILE
5. print the last field of every input line: awk '{ print $NF }' SOMEFILE
6. print the first 50 characters of each line. if a line has fewer than 50 characters, then the line is padded with spaces. awk '{ printf("%-50.50s\n", $0) }' SOMEFILE
7. sum the values in column 1 awk 'BEGIN{total=0;} {total += $1;} END{print "total is ", total}' SOMEFILE
8. sum the values in columns 1, 2 and 4 in order to calculate precision and recall awk -F ',' 'BEGIN{TP=0; FP=0; FN=0} {TP += $1; FP += $2; FN += $4} END{print "precision is ", TP/(FP+TP); print "recall is ", TP/(FN+TP)}' prec-recall-2states.txt
9. sum each row awk '{sum=0; for(i=1; i<=NF; i++){sum+=$i}; print sum}' SOMEFILE

1. Simple test BEGIN { print ARGV[0] " " ARGV[1] " " ARGV[2] } { print "TotRec " NR " RecNum " FNR " RecSep " RS " RecTer " RT " NumFie " NF " FileSep " FS print $0 next; }
2. BEGIN { FS = OFS = ","; } FNR == NR { Descr[$1,$2] = $3; next; } { if (($3,$4) in Descr) print $0,Descr[$3,$4]; else print $0,"Unknown Account"; }

Notes: This one is the standard C quine with main replaced by BEGIN. 
BEGIN{c="BEGIN{c=%c%s%c;printf(c,34,c,34);}";printf(c,34,c,34);}

BEGIN{c="BEGIN{c=%c%s%c;printf c,34,c,34}";printf c,34,c,34}