Links & files

Awk reference and ressources	Example files
gnu.org	`mail-list`
oreilly effective awk programming	`inventory-shipped`

📑 Expressions#

Constants, Variables, and Conversions#

Constant expressions#

Three kinds of constants: numeric, string, and regexp.

Numeric and string constants
Octal and hexadecimal numbers

awk 'BEGIN { printf "%d, %d, %d\n", 011, 11, 0x11 }'

Regular expression constants

Using regular expression constants#

ls -1 | awk '{
if ($0 ~ /name/ || $0 ~ /phone/) print $0
}'

is exactly equivalent to

ls -1 | awk '{
if (/name/ || /phone/) print $0
}'

Constant regular expressions are also used:

as the first argument for the gensub() , sub() , and gsub() functions
as the second argument of the match() function
as the third argument of the split() and patsplit() functions

Variables#

Variables assignments:

variable=text
-v variable=text

awk '{ print $n }' n=4 inventory-shipped n=2 mail-list

awk -v n=4 '{ print $n }' inventory-shipped n=2 mail-list

Conversion of strings and numbers#

awk program make conversion if the context demands it.

awk 'BEGIN { t = 2 ; r = 3
print (t r) + 3
print t + r + 3
print t r 3
}'

26
8
233

CONVFMT The conversion format for numbers, “%.6g”, by default.

Locales can influence conversion#

Locale decimal point versus a period

Feature	Default	–posix or –use-lc-numeric
%’g	Use locale	Use locale
%g	Use period	Use locale
Input	Use period	Use locale
strtonum()	Use period	Use locale

export export POSIXLY_CORRECT=1
gawk 'BEGIN { printf "%g\n", 3.1415927 }'

3.14159

LC_ALL=fr_FR.utf8 gawk 'BEGIN { printf "%g\n", 3.1415927 }'

3,14159

echo 4,321 | gawk '{ print $1 + 1 }'

5

echo 4,321 | LC_ALL=fr_FR.utf-8 gawk '{ print $1 + 1 }'

5,321

Operators: Doing Something with Values#

Arithmetic Operators#

x ^ y	exponentiation
x y**	exponentiation
- x	negation
+ x	unary plus
*x y**	multiplication
x / y	division
x % y	remainder
x + y	addition
x - y	subtraction

cat grades
Pat   100 97 58
Sandy 84 72 93
Chris 72 92 89

awk '{ sum = $2 + $3 + $4 ; avg = sum / 3
     printf "%-5s => %d\n", $1, avg }' grades

String Concatenation#

There is only one string operation: concatenation with no operator.

awk 'BEGIN { print -12 " " -24 }'
-12-24
awk 'BEGIN { print -12 " " (-24) }'
-12 -24

Assignment Expressions#

Multiple assignments:

x = y = z = 5

Operator	Effect
lvalue += increment	add increment to the value of lvalue
lvalue -= decrement	subtract decrement from the value of lvalue
*lvalue = coefficient**	multiply the value of lvalue by coefficient
lvalue /= divisor	divide the value of lvalue by divisor
lvalue %= modulus	set lvalue to its remainder by modulus
lvalue ^= power	raise lvalue to the power power
lvalue = power**	raise lvalue to the power power (c.e.)

Increment and Decrement Operators#

++lvalue	increment lvalue , returning the new value as the value of the expression
lvalue++	increment lvalue , returning the old value of lvalue as the value of the expression
- -lvalue	decrement lvalue , returning the new value as the value of the expression
lvalue- -	decrement lvalue , returning the old value of lvalue as the value of the expression

awk 'BEGIN { max = 3
    for (i=1; i <= max; i++)
        printf "file_%.3d\n", i
}'

Truth Values and Conditions#

True and False in awk#

true	any nonzero numeric value or any nonempty string value
false	any other value (zero or the null string, “” )

Variable Typing and Comparison Expressions#

String type versus numeric type#

UPPER operand type

lower comparison type

	STRING	NUMERIC	STRNUM
STRING	string	string	string
NUMERIC	string	numeric	numeric
STRNUM	strig	numeric	numeric

Comparison operators#

Expression	Result
x < y	true if x is less than y
x <= y	true if x is less than or equal to y
x > y	true if x is greater than y
x >= y	true if x is greater than or equal to y
x == y	true if x is equal to y
x != y	true if x is not equal to y
x ~ y	true if the string x matches the regexp denoted by y
x !~ y	true if the string x does not match the regexp denoted by y
subscript in array	true if the array array has an element with the subscript subscript

String comparison with POSIX rules#

POSIX string comparison is performed based on the locale’s collating order.

awk 'BEGIN { printf("ABC < abc = %s\n",
                   ("ABC" < "abc" ? "TRUE" : "FALSE")) }'
ABC < abc = TRUE

awk --posix 'BEGIN { printf("ABC < abc = %s\n",
                   ("ABC" < "abc" ? "TRUE" : "FALSE")) }'
ABC < abc = FALSE

Boolean Expressions#

“or”	\|\|	boolean1 \|\| boolean2	true if boolean1 or boolean2 is true
“and”	&&	boolean1 && boolean2	true if both boolean1 and boolean2 are true
“not”	!	! boolean	true if boolean is false

awk 'BEGIN { if (! ("HOME" in ENVIRON))
print "no home!" }'

Conditional Expressions#

selector ? if-true-exp : if-false-exp

awk 'BEGIN { "whoami" | getline who_ami ; close("whoami")
     printf "%s\n%s\n", ( who_ami ~ /guillaume|guigui/ ? "guisam is here" : "no guisam here" ), "bye"
     exit }'

Function Calls#

Function calls return a value that may be used.

function(argument)

awk '{ print "The square root of", $1, "is", sqrt($1) }'

Type crtl-d to terminate.

Operator Precedence (How Operators Nest)#

Operators in order of highest to lowest precedence
Operator	Description
( … )	grouping
$	field reference
++ –	increment, decrement
^ **	exponentiation, these operators group right to left
+ - !	unary plus, minus, logical “not.”
* / %	multiplication, division, remainder
+ -	addition, subtraction
no operator	string concatenation
< <= == != > >= >> \| \|&	relational and redirection
~ !~	matching, nonmatching
in	array membership
&&	logical “and.”
\|\|	logical “or.”
?:	conditional, this operator groups right to left
*= += -= = /= %= ^= =	assignment, these operators group right to left

Where You Are Makes a Difference#

Locales can affect dates, times, the value of the decimal point character. Setting “LC_ALL=C” in the environment will give you much better performance.

📑 Expressions

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