AWK

# Set input field separator to colon
awk -F: '{print $1}' /etc/passwd

# Set input and output separators
awk 'BEGIN{FS=":"; OFS="\t"} {print $1, $3}' /etc/passwd

# Use a regex as field separator (gawk)
awk -F'[,;:]' '{print $1, $2}' file

# Use null byte as record separator for paragraph mode
awk 'BEGIN{RS=""} {print NR, $0}' file

awk 'BEGIN { <initialization> } <pattern> { <action> } END { <cleanup> }' <file>

/regex/              # Regular expression match
$3 > 100             # Expression (field comparison)
/start/,/end/        # Range pattern (inclusive)
NR == 5              # Specific line number
NR % 2 == 0          # Every even line

awk '/pattern/ {print "$1"}'    # standard Unix shells

awk '/pattern/ {print "$1"}'    # compiled with DJGPP, Cygwin
awk "/pattern/ {print \"$1\"}"  # GnuWin32, UnxUtils, Mingw

# 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"}'

# 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}'

# 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-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

# Process a large CSV efficiently: set FS once, exit early on match
awk -F, 'BEGIN{OFS=","} $3 == "ERROR" {print; count++} END{print count " errors found"}' large.csv

# Parallel processing with GNU parallel and awk
parallel --pipepart -a large.csv --block 10M awk -F, "'{print \$1, \$3}'"