Awk Cheat Sheet

Process and transform structured text field by field.

Basic Syntax

awk [OPTIONS] 'program' [FILE...]
awk -F: 'program' [FILE...]          # set field separator to :
awk -v var=value 'program' [FILE...] # pass variable from shell

Built-in Variables

Variable	Meaning
$0	Entire current line
$1, $2, $NF	Field 1, field 2, last field
NF	Number of fields in current record
NR	Current record (line) number
FNR	Record number within current file
FS	Field separator (default: whitespace)
OFS	Output field separator (default: space)
RS	Record separator (default: newline)
ORS	Output record separator
FILENAME	Name of current input file

Program Structure

BEGIN { setup }    # runs once before input
/pattern/ { action }  # runs when pattern matches
{ action }         # runs for every line
END { summary }    # runs once after all input

Common Patterns

# Print specific field
awk '{print $1}' file.txt
awk -F: '{print $1, $7}' /etc/passwd    # fields 1 and 7, space-separated
awk -F: '{print $1 ":" $7}' /etc/passwd # with custom separator

# Conditional
awk '$3 > 1000 {print $1}' /etc/passwd  # lines where field 3 > 1000
awk '/error/ {print NR, $0}' log.txt    # numbered error lines
awk 'NF > 3' data.txt                   # lines with more than 3 fields

# Sum a column
awk '{sum += $1} END {print sum}' numbers.txt

# Count matches
awk '/error/ {count++} END {print count}' log.txt

# Average
awk '{sum += $1; n++} END {print sum/n}' numbers.txt

# Print last field
awk '{print $NF}' file.txt

# Print all except first field
awk '{$1=""; print $0}' file.txt

# Format output with printf
awk '{printf "%-20s %5d\n", $1, $2}' data.txt

Text Transformation

# Swap fields
awk '{print $2, $1}' file.txt

# Change delimiter (CSV to TSV)
awk -F, '{print $1 "\t" $2 "\t" $3}' data.csv

# Add header line
awk 'BEGIN {print "NAME UID SHELL"} -F: {print $1, $3, $7}' /etc/passwd

# Skip header and process data
awk 'NR > 1 {print $1, $2}' data.csv

# Print lines between two patterns
awk '/START/,/END/' file.txt

Associative Arrays (awk maps)

# Count by category
awk '{count[$2]++} END {for (k in count) print k, count[k]}' data.txt

# Find unique values in field 1
awk '!seen[$1]++' file.txt

# Accumulate per key
awk '{sum[$1] += $2} END {for (k in sum) print k, sum[k]}' data.txt

Common Recipes

# Lines longer than 80 characters
awk 'length($0) > 80' file.txt

# Remove duplicate lines (keeping order)
awk '!seen[$0]++' file.txt

# Count requests per IP in access log
awk '{print $1}' access.log | sort | uniq -c | sort -rn | head -10

# Sum file sizes from ls -l
ls -l | awk 'NR > 1 {sum += $5} END {print "Total:", sum, "bytes"}'

# Print lines where field 2 matches pattern
awk '$2 ~ /pattern/' data.txt

# Print lines where field 2 does NOT match
awk '$2 !~ /pattern/' data.txt

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Related: grep, sed, pipes-redirection