Detailed explanation and examples of awk

AWK language

V option:

-F: indicates the field delimiter used when entering

-v var=value: define variables

V delimiters, fields, and records

When awk is executed, the field (field) separated by a delimiter is marked $1 ~ 2.

Identifies the domain. $0 is all fields. Note: the meaning of the variable $symbol in shell is different.

Each line of the file is called a record

If the action line is omitted, the print $0

$0: print all

V example:

Awk'{print "hello,awk"}'

Awk-F:'{print}'/ etc/passwd

Awk-F:'{print "wang"}'/ etc/passwd

Awk-F:'{print $1}'/ etc/passwd

Awk-F:'{print $0}'/ etc/passwd

Awk-F:'{print $1 "\ t" $3}'/ etc/passwd

Tail-3 / etc/fstab | awk'{print $2 recording 4}'

Awk variable

V variables: built-in and custom variabl

V FS: enter the field delimiter, which defaults to a blank character

Awk-v FS=':''{print $1m FS journal 3}'/ etc/passwd

Awk-F:'{print $1, 3, 7}'/ etc/passwd

V OFS: output field delimiter, default is white space character

Awk-v FS=':'-v OFS=':''{print $1 recording 3 memes 7}'/ etc/passwd

VRS: enter the record delimiter and specify the newline character when entering. The original newline character is still valid.

Awk-v RS='''{print}'/ etc/passwd

V ORS: output record delimiter, using the specified symbol instead of the newline character

Awk-v RS=''- v ORS='###'' {print}'/ etc/passwd

Print odd or even lines:

Some simple methods of calculation

Count the number of words in a file:

NF: number of field

Awk-FRV:'{print NF}'/ etc/fstab, no $is needed to refer to the built-in variable

Awk-F:'{print $(NF-1)}'/ etc/passwd

V NR: line number

FNR: count each file separately, line number

Awk'{print FNR}'/ etc/fstab / etc/inittab

FILENAME: current file name

Awk'{print FILENAME}'/ etc/fstab

Print out the file name when you print it out.

ARGC: the number of command line arguments

Awk'{print ARGC}'/ etc/fstab / etc/inittab

Awk 'BEGIN {print ARGC}' / etc/fstab / etc/inittab

V ARGV: array that holds the parameters given by the command line

Custom variables (case sensitive)

(1)-v var=value

(2) in program

The difference between putting variables in {} and outside:

{} inside: assign a value each time it is executed

{} outside: assign values before execution and recycle later

-f: invoke the script

Printf command

There are several variables behind, and there should be several format definitions in front of them, that is, several% definitions, percent sign definitions and variables should correspond one to one.

V formatted output: printf "FORMAT", item1, item2,...

(1) FORMAT must be specified

(2) the line wrapping will not occur automatically, and the newline control character needs to be given explicitly,\ n

(3) format characters need to be specified for each subsequent item in FORMAT

V format character: one-to-one correspondence with item

% c: ASCII code for display characters

% d,% I: show decimal integers

% e,% E: display scientific counting values

% f: displayed as a floating point number

10.3: a total of 10 digits, including 3 zeros, one decimal point

% g,% G: display values in scientific counting or floating point form

% s: display string

% u: unsigned integer

The following figure shows 10 characters:

%%: show% itself

V modifier:

# [. #]: the first number controls the width of the display; the second # indicates the precision after the decimal point,% 3.1f

-: left alignment (default right alignment)%-15s

+ sign: displays the plus or minus sign% + d of the numeric value

BEGIN: add a header in front of it

Operator

V arithmetic operator:

X% y, x ^ y, x% y

-x: convert to negative number

+ x: convert to numeric value

V string operator: unsigned operator, string concatenation

V assignment operator:

=, +, -, *, /,%, ^ =

+,-

V comparison operator:

=,!, >, >, v2?var=v1:var=v2

Return var

}

BEGIN {axiom 3 / b / b / 2 / print max (b)}

Awk script

V will write the awk program as a script, which can be called or executed directly

V example:

# cat f1.awk

{if ($3 > = 1000) print $1

# awk-F:-f f1.awk / etc/passwd

# cat f2.awk

#! / bin/awk-f

# this is an awk script

{if ($3 > = 1000) print $1

# chmod + x f2.awk

# f2.awk-F: / etc/passwd

Pass parameters to the awk script

V format:

Awkfile var=value var2=value2... Inputfile

V Note: not available during BEGIN. Until the first line of input is complete, change

Quantity is only available. You can use the-v parameter to let awk get it before executing BEGIN

The value of the variable Each specified variable on the command line requires a-v argument

V example:

# cat test.awk

#! / bin/awk-f

{if ($3 > = min & & $3)