- The GNU Awk User's Guide (www-zeuthen.desy.de)
- AWK cheatsheet (gist.github.com)
Awk Cheat Sheet
This is a one page quick reference cheat sheet to the GNU awk, which covers commonly used awk expressions and
Also see
Miscellaneous
Run script
$ cat demo.awk
#!/usr/bin/awk -f
BEGIN { x = 23 }
{ x += 2 }
END { print x }
$ awk -f demo.awk /etc/passwd
69
Escape Sequences
- | - |
---|---|
\b |
Backspace |
\f |
Form feed |
\n |
Newline (line feed) |
\r |
Carriage return |
\t |
Horizontal tab |
\v |
Vertical tab |
Regex Metacharacters
\
^
$
.
[
]
|
(
)
*
+
?
Awk Formatted Printing
Header
awk -F: 'BEGIN {
printf "%-10s %s\n", "User", "Home"
printf "%-10s %s\n", "----","----"}
{ printf "%-10s %s\n", $1, $(NF-1) }
' /etc/passwd | head -n 5
Outputs
User Home
---- ----
root /root
bin /bin
daemon /sbin
Space
awk -F: '{
printf "%-10s %s\n", $1, $(NF-1)
}' /etc/passwd | head -n 3
Outputs
root /root
bin /bin
daemon /sbin
Common specifiers
Character | Description |
---|---|
c |
ASCII character |
d |
Decimal integer |
e , E , f |
Floating-point format |
o |
Unsigned octal value |
s |
String |
% |
Literal % |
Awk Conditions
switch
awk -F: '{
switch (NR * 2 + 1) {
case 3:
case "11":
print NR - 1
break
case /2[[:digit:]]+/:
print NR
default:
print NR + 1
case -1:
print NR * -1
}
}' /etc/passwd
if-else statement
awk -v count=2 'BEGIN {
if (count == 1)
print "Yes";
else
print "Huh?";
}'
#Ternary operator
awk -v count=2 'BEGIN {
print (count==1) ? "Yes" : "Huh?";
}'
Awk Arrays
Multi-dimensional iteration
awk 'BEGIN {
array[1,2]=3;
array[2,3]=5;
for (comb in array) {
split(comb,sep,SUBSEP);
print sep[1], sep[2],
array[sep[1],sep[2]]
}
}'
Multi-dimensional
awk 'BEGIN {
multidim[0,0] = "foo";
multidim[0,1] = "bar";
multidim[1,0] = "baz";
multidim[1,1] = "boo";
}'
Array with asort
awk 'BEGIN {
arr[0] = 3
arr[1] = 2
arr[2] = 4
n = asort(arr)
for (i = 1; i <= n ; i++)
print(arr[i])
}'
Array with split
awk 'BEGIN {
split("foo:bar:baz", arr, ":");
for (key in arr)
print arr[key];
}'
Array with key
awk 'BEGIN {
assoc["foo"] = "bar";
assoc["bar"] = "baz";
print("baz" in assoc); # => 0
print("foo" in assoc); # => 1
}'
Array with index
awk 'BEGIN {
arr[0] = "foo";
arr[1] = "bar";
print(arr[0]); # => foo
delete arr[0];
print(arr[0]); # => ""
}'
Awk Functions
User defined function
awk '
# Returns minimum number
function find\_min(num1, num2){
if (num1 < num2)
return num1
return num2
}
# Returns maximum number
function find\_max(num1, num2){
if (num1 > num2)
return num1
return num2
}
# Main function
function main(num1, num2){
result = find\_min(num1, num2)
print "Minimum =", result
result = find\_max(num1, num2)
print "Maximum =", result
}
# Script execution starts here
BEGIN {
main(10, 60)
}
'
Common functions
Function | Description |
---|---|
index(s,t) |
Position in string s where string t occurs, 0 if not found |
length(s) |
Length of string s (or $0 if no arg) |
rand |
Random number between 0 and 1 |
substr(s,index,len) |
Return len-char substring of s that begins at index (counted from 1) |
srand |
Set seed for rand and return previous seed |
int(x) |
Truncate x to integer value |
split(s,a,fs) |
Split string s into array a split by fs, returning length of a |
match(s,r) |
Position in string s where regex r occurs, or 0 if not found |
sub(r,t,s) |
Substitute t for first occurrence of regex r in string s (or $0 if s not given) |
gsub(r,t,s) |
Substitute t for all occurrences of regex r in string s |
system(cmd) |
Execute cmd and return exit status |
tolower(s) |
String s to lowercase |
toupper(s) |
String s to uppercase |
getline |
Set $0 to next input record from current input file. |
Awk Variables
Defining variable
awk -v var1="Hello" -v var2="Wold" '
END {print var1, var2}
' </dev/null
#Use shell variables
awk -v varName="$PWD" '
END {print varName}' </dev/null
GNU awk only
- | - |
---|---|
ENVIRON |
Environment variables |
IGNORECASE |
Ignore case |
CONVFMT |
Conversion format |
ERRNO |
System errors |
FIELDWIDTHS |
Fixed width fields |
Environment Variables
- | - |
---|---|
ARGC |
Number or arguments |
ARGV |
Array of arguments |
FNR |
F ile N umber of R ecords |
OFMT |
Format for numbers (default "%.6g") |
RSTART |
Location in the string |
RLENGTH |
Length of match |
SUBSEP |
Multi-dimensional array separator (default "\034") |
ARGIND |
Argument Index |
Examples
Print sum and average
awk -F: '{sum += $3}
END { print sum, sum/NR }
' /etc/passwd
Printing parameters
awk 'BEGIN {
for (i = 1; i < ARGC; i++)
print ARGV[i] }' a b c
Output field separator as a comma
awk 'BEGIN { FS=":";OFS=","}
{print $1,$2,$3,$4}' /etc/passwd
Position of match
awk 'BEGIN {
if (match("One Two Three", "Tw"))
print RSTART }'
Length of match
awk 'BEGIN {
if (match("One Two Three", "re"))
print RLENGTH }'
Expressions
- | - |
---|---|
$1 == "root" |
First field equals root |
{print $(NF-1)} |
Second last field |
NR!=1{print $0} |
From 2th record |
NR > 3 |
From 4th record |
NR == 1 |
First record |
END{print NR} |
Total records |
BEGIN{print OFMT} |
Output format |
{print NR, $0} |
Line number |
{print NR " " $0} |
Line number (tab) |
{$1 = NR; print} |
Replace 1th field with line number |
$NF > 4 |
Last field > 4 |
NR % 2 == 0 |
Even records |
NR==10, NR==20 |
Records 10 to 20 |
BEGIN{print ARGC} |
Total arguments |
ORS=NR%5?",":"\n" |
Concatenate records |
Build-in variables
- | - |
---|---|
$0 |
Whole line |
$1, $2...$NF |
First, second⦠last field |
NR |
N umber of R ecords |
NF |
N umber of F ields |
OFS |
O utput F ield S eparator (default " ") |
FS |
input F ield S eparator (default " ") |
ORS |
O utput R ecord S eparator (default "\n") |
RS |
input R ecord S eparator (default "\n") |
FILENAME |
Name of the file |
Getting Started
Generate 1000 spaces
awk 'BEGIN{
while (a++ < 1000)
s=s " ";
print s
}'
See: Loops
Conditions
awk -F: '$3>30 {print $1}' /etc/passwd
See: Conditions
Awk program examples
awk 'BEGIN {print "hello world"}' # Prints "hello world"
awk -F: '{print $1}' /etc/passwd # -F: Specify field separator
# /pattern/ Execute actions only for matched pattern
awk -F: '/root/ {print $1}' /etc/passwd
# BEGIN block is executed once at the start
awk -F: 'BEGIN { print "uid"} { print $1 }' /etc/passwd
# END block is executed once at the end
awk -F: '{print $1} END { print "-done-"}' /etc/passwd
Variables
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# First and last field
awk -F: '{print $1,$NF}' /etc/passwd
# With line number
awk -F: '{print NR, $0}' /etc/passwd
# Second last field
awk -F: '{print $(NF-1)}' /etc/passwd
# Custom string
awk -F: '{print $1 "=" $6}' /etc/passwd
See: Variables
Awk program
BEGIN {<initializations>}
<pattern 1> {<program actions>}
<pattern 2> {<program actions>}
...
END {< final actions >}
#Example
awk '
BEGIN { print "\n>>>Start" }
!/(login|shutdown)/ { print NR, $0 }
END { print "<<<END\n" }
' /etc/passwd
Have a try
$ awk -F: '{print $1, $NF}' /etc/passwd
- | - | - |
---|---|---|
-F: |
Colon as a separator | |
{...} |
Awk program | |
print |
Prints the current record | |
$1 |
First field | |
$NF |
Last field | |
/etc/passwd |
Input data file |