Shulou(Shulou.com)06/01 Report--

This article mainly introduces how to use awk, has a certain reference value, interested friends can refer to, I hope you can learn a lot after reading this article, the following let the editor take you to understand it.

1. First of all, a brief summary of some text processing three Musketeers:

Grep families: text filtering tool

Sed: line editing tool

two。 Let's take a look at what awk is.

Awk now uses GNU awk, or gawk, on linux, and awk is now a symbolic link file for gawk on centos systems. So what exactly is awk used for on centos systems? Awk is a report generator, a tool for formatting text output.

3. What is the help of learning awk?

Learning awk, we can easily view the text we want to deal with, etc., to facilitate us to solve problems.

4. The basic usage of gawk:

Gawk-pattern scanning and processing language mode scanning and processing language

Syntax: gawk [options] 'program' file...

To elaborate on the following:

4.1 [options]:

-F indicates the field separator at the time of input

-v VAR=VALUE is mainly used to implement custom variables

4.2 program:PATTERN {ACTION STATEMENTS}

Statements are separated by semicolons

Built-in command: print,printf

5. The variables used in the

5.1Variables (Note: you can't add a $sign to your own variables in awk, which is different from bash)

Built-in variables:

FS:input field seperator input field delimiter, which defaults to blank characters

This is equivalent to the-F delimiter

OFS:output field seperator output field delimiter, which defaults to a blank character

Eg:

[root@bucktan ~] # tail-2 / etc/fstab | awk-v OFS=':''{print $1J 3}'

Sysfs:sysfs

Proc:proc

[root@bucktan] # tail-2 / etc/fstab

Sysfs / sys sysfs defaults 0 0

Proc / proc proc defaults 0 0

[root@bucktan ~] # tail-2 / etc/passwd | awk-v FS=':''{print $1J 3}'

Apple 2000

Zabbix 495

RS:input record sepereator specifies the newline character when entering

ORS:output record sepereator specifies the newline character for output

Eg:

[root@bucktan ~] # awk-v RS=''- v ORS='##''{print}'/ etc/passwd

Root:x:0:0:root:/root:/bin/bash

Bin:x:1:1:bin:/bin:/sbin/nologin

Daemon:x:2:2:daemon:/sbin:/sbin/nologin

Adm:x:3:4:adm:/var/adm:/sbin/nologin

Lp:x:4:7:lp:/var/spool/lpd:/sbin/nologin

Sync:x:5:0:sync:/sbin:/bin/sync

Shutdown:x:6:0:shutdown:/sbin:/sbin/shutdown

Halt:x:7:0:halt:/sbin:/sbin/halt

Mail:x:8:12:mail:/var/spool/mail:/sbin/nologin

Uucp:x:10:14:uucp:/var/spool/uucp:/sbin/nologin

Operator:x:11:0:operator:/root:/sbin/nologin

Games:x:12:100:games:/usr/games:/sbin/nologin

Gopher:x:13:30:gopher:/var/gopher:/sbin/nologin

Ftp:x:14:50:FTP##User:/var/ftp:/sbin/nologin

Nobody:x:99:99:Nobody:/:/sbin/nologin

Dbus:x:81:81:System##message##bus:/:/sbin/nologin

Pay attention to the # in it.

NF:number of field counts the number of fields in each row

{print NF}

{print $NF}: print the last field

~] # awk'{print NF}'/ etc/passwd

Eg:

[root@bucktan ~] # awk-F:'{print $NF}'/ etc/passwd

NR:number of record prints the line number of each line, but in fact counts the total number of lines in the file

FNR: count each file and count the lines separately

FILENAME: the name of the file currently being processed

ARGC: the number of command line arguments

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

ARGV [0]: the first parameter

.

Eg:

[root@bucktan ~] # awk 'BEGIN {print ARGV [0]}' / etc/passwd / etc/fstab

Awk

[root@bucktan ~] # awk 'BEGIN {print ARGV [1]}' / etc/passwd / etc/fstab

/ etc/passwd

Note: the purpose of BEGIN is to achieve results that are not printed on each line. If there is no BEGIN, each line will display a printed value

5.2 Custom variables:

(1):-v var=value variable name is case sensitive

(2): define directly in program

Eg:

[root@bucktan ~] # awk-v abc='love you''{print abc}'/ etc/passwd

Another implementation:

[root@bucktan ~] # awk 'BEGIN {abc= "love you"; print abc}'

Love you

Syntax: gawk [options] 'program' file...

Program:PATTERN {ACTION STATEMENTS}

6. Built-in commands in it

6.1:print (used in {ACTION STATEMENTS})

Print iterm1,iterm2, .

Main points: (1): commas are delimiters, but blank characters are displayed instead of commas when output

(2): each output iterm can be a string, numeric value, field of the current record, variable, or expression of awk

(3): if iterm is omitted, it is equivalent to print$0

Eg:

[root@bucktan ~] # tail-5 / etc/passwd | awk-F:'{print "hehe:

Hehe:111tcpdump 72

Hehe:111bucktan 500

Hehe:111centos 496

Hehe:111apple 2000

Hehe:111zabbix 495

[root@bucktan ~] # tail-2 / etc/passwd | awk-F:'{print}'

Apple:x:2000:2000::/home/apple:/bin/bash

Zabbix:x:495:492:Zabbix Monitoring System:/var/lib/zabbix:/sbin/nologin

6.2 printf Command

Printf-format and print

Formatted output: printf FORMAT iterm1,iterm2,...

Main points: (1): FORMAT: must be given

(2): it will not wrap automatically. You need to show the newline control character to know which line.

(3): in FORMAT, you need to specify a format symbol for each subsequent iterm.

Format character:

% c: ASCII code that displays characters

% dline% I: display decimal integers

% eGraine% E: scientific counting method numerical display

% gpeng% G: display values in scientific counting or floating-point form

% s: display string

% u: unsigned integer

%%: show% itself

Style one

[root@bucktan ~] # awk-F:'{printf "% s", $1}'/ etc/passwd

Rootbindaemonadmlpsyncshutdownhaltmailuucpoperatorgamesgopherftpnobodydbususbmuxdvcsarpcrtkitavahi-autoipdabrtrpcusernfsnobodyhaldaemongdmntpapache

Style two

[root@bucktan ~] # awk-F:'{printf "% s\ n", $1}'/ etc/passwd

Root

Bin

Daemon

Adm

Lp

Style three

[root@bucktan ~] # awk-F:'{printf "username:% s\ n", $1}'/ etc/passwd

Username: root

Username: bin

Username: daemon

Username: adm

Username: lp

Style four

[root@bucktan ~] # awk-F:'{printf "username:% s, userid:% s\ n", $1 printf 3}'/ etc/passwd

Username: root, userid: 0

Username: bin, userid: 1

Username: daemon, userid: 2

Username: adm, userid: 3

Username: lp, userid: 4

Username: sync, userid: 5

Username: shutdown, userid: 6

Username: halt, userid: 7

Username: mail, userid: 8

Modifier:

# [. #]: the first number controls the width of the display: the second # represents the precision of the decimal point

Such as% 3.1f

-: align left, do not add-default right alignment

+: symbols that display numeric values

[root@bucktan ~] # awk-F:'{printf "username:%-15s, userid:% s\ n", $1 printf 3}'/ etc/passwd

Username: root, userid: 0

Username: bin, userid: 1

Username: daemon, userid: 2

# # omitting later content

7. Operator

# (also used in execution statements, remember to separate the semicolon from the print built-in command)

Arithmetic operator:

Xquoy, xMelector x* | / | ^ |% y

-x: negative valu

+ x: convert to numeric value

String operators: unsigned operators, string concatenation

Assignment operators: =, +, -, *, /,% =, +,--

Comparison operator: >, =

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