Print specific columns from a file

awk '{print $1, $3}' file.txt

Print with custom field separator (CSV)

awk -F',' '{print $1, $2}' data.csv

Filter rows by column value

awk '$3 > 100 {print $1, $3}' data.txt

Compute sum of a column

awk '{sum += $2} END {print sum}' data.txt

Print formatted report with headers

awk 'BEGIN {print "Name\tScore"} {print $1 "\t" $2}' data.txt

Count lines per category

awk '{count[$1]++} END {for (c in count) print c, count[c]}' data.txt

Can be used to execute arbitrary commands on a system and spawn shells.

awk 'BEGIN{system("/bin/sh")}'

Can be used to execute arbitrary commands on a system.

awk 'BEGIN {system("ls"); exit}' /dev/null

The file must exist and command will be executed as many rows there are in the file.

awk 'system("ls")' /etc/passwd

If spaces cannot be inserted, we can use `sprintf(%c,32)` to emulate them.

awk '//{}BEGIN{system(sprintf("uname%c-aa",32))}'

Read an arbitrary file.

awk 'BEGIN{while((getline line<"/etc/passwd")>0){print line}}' /dev/null

Argument injection: execute arbitrary command: Can be used to execute arbitrary commands on a system.

awk 'BEGIN {system("ls"); exit}' /dev/null

Argument injection: execute arbitrary command: The file must exist and command will be executed as many rows there are in the file.

awk 'system("ls")' /etc/passwd

Argument injection: execute arbitrary command: If spaces cannot be inserted, we can use `sprintf(%c,32)` to emulate them.

awk '//{}BEGIN{system(sprintf("uname%c-aa",32))}'

Argument injection: read local file: Read an arbitrary file.

awk 'BEGIN{while((getline line<"/etc/passwd")>0){print line}}' /dev/null

Argument injection: read local file: Print the contents of multiple files.

awk '//' /etc/passwd /etc/hostname /root/.ssh/id_rsa

Argument injection: write to local file: Write to an arbitrary file

awk 'BEGIN{print "ssh-rsa ..." > "/root/.ssh/authorized_keys}' /dev/null

Sum integers from a file or STDIN, one integer per line.

printf '1\n2\n3\n' | awk '{sum += $1} END {print sum}'

Using specific character as separator to sum integers from a file or STDIN.

printf '1:2:3' | awk -F ":" '{print $1+$2+$3}'

Print line number 12 of file.txt

awk 'NR==12' file.txt

Print first field for each record in file.txt

awk '{print $1}' file.txt

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Print only lines that match regex in file.txt

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awk '/regex/' file.txt

Print only lines that do not match regex in file.txt

awk '!/regex/' file.txt

Print any line where field 2 is equal to "foo" in file.txt

awk '$2 == "foo"' file.txt

Print lines where field 2 is NOT equal to "foo" in file.txt

awk '$2 != "foo"' file.txt

Print line if field 1 matches regex in file.txt

awk '$1 ~ /regex/' file.txt

Print line if field 1 does NOT match regex in file.txt

awk '$1 !~ /regex/' file.txt

Print lines with more than 80 characters in file.txt

awk 'length > 80' file.txt

Print a multiplication table.

awk -v RS='' '

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{

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for(i=1;i<=NF;i++){

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printf("%dx%d=%d%s", i, NR, i*NR, i==NR?"\n":"\t")

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}

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}

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' <<< "$(seq 9 | sed 'H;g')"

Specify output separator character.

printf '1 2 3' | awk 'BEGIN {OFS=":"}; {print $1,$2,$3}'

Search paragraph for the given REGEX match. Paragraphs will be collapsed together.

awk -v RS='' '/42B/' file

Search paragraph for the given REGEX match. Paragraphs will be separated with a new line.

awk -v RS= ORS='\n\n' '/42B/' file

Display only first field in text taken from STDIN.

echo 'Field_1  Field_2  Field_3' | awk '{print $1}'

Use AWK solo; without the need for something via STDIN.

awk 'BEGIN {print("Example text.")}'

Access environment variables from within AWK.

awk 'BEGIN {print ENVIRON["LS_COLORS"]}'

Count number of lines taken from STDIN.

free | awk '{L++} END {print(L)}'

Cleaner, more efficient approach to the above.

free | awk 'END {print(NR)}'

Output unique list of available sections under which to create a DEB package.

awk '!A[$1]++ {print($1)}' <<< "$(dpkg-query --show -f='${Section}\n')"

Using process substitution (`<()` is NOT command substitution), with AWK and its associative array variables, we can print just column 2 for lines whose first column is equal to what's between the double-quotes.

awk '{NR != 1 && A[$1]=$2} END {print(A["Mem:"])}' <(free -h)

While below is an easier and simpler solution to the above, it's not at all the same, and in other cases, the above is definitely preferable.

awk '/^Mem:/ {print($2)}' <(free -h)

Output list of unique uppercase-only, sigil-omitted variables used in FILE.

awk '

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{

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for(F=0; F<NF; F++){

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if($F~/^\$[A-Z_]+$/){

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A[$F]++

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}

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}

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}

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END {

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for(I in A){

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X=substr(I, 2, length(I))

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printf("%s\n", X)

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}

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}

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' FILE

Output only lines from FILE between PATTERN_1 and PATTERN_2. Good for logs.

awk '/PATTERN_1/,/PATTERN_2/ {print}' FILE

Pretty-print a table of an overview of the non-system users on the system.

awk -F ':' '

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BEGIN {

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printf("%-17s %-4s %-4s %-s\n", "NAME", "UID", "GID", "SHELL")

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}

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$3 >= 1000 && $1 != "nobody" {

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printf("%-17s %-d %-d %-s\n", $1, $3, $4, $7)

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}

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' /etc/passwd

Display the total amount of MiB of RAM available in the machine. This is also a painful but useful workaround to get the units comma-separated, as would be doable with Bash's own `printf` built-in.

awk '/^MemTotal:/ {printf("%'"'"'dMiB\n", $2 / 1024)}'

It's possible to sort strings in AWK, as well as uniq-ing, meaning you can replace uniq(1) and sort(1) calls with just the one call of AWK. Granted, you can use `sort -u` to do both, but AWK offers much more functionality. Unlike when using AWK to uniq-ify, uniq(1) only works by adjacency, meaning the duplicate lines must be adjacent to one another for them to be handled.

awk '

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{

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!Lines[$0]++

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}

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END {

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asorti(Lines, Sorted)

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for (Line in Sorted) {

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print(Sorted[Line])

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}

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}

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' FILE

Remove duplicate lines

awk '!seen[$0]++' file.txt

Remove all empty lines

awk 'NF > 0' file.txt