Powerful query character matching commands and shell scripts in Linux

Variable:

Local variable: valid only for the current

Environment variable: valid for both the current shell and sub-shell

Export A = 3 define a as a variable and assign 3 to

A = 3

Export a reference does not need to be added &

Export also views Environment Variables

[Root @ server56 ~] # Export

Declare-x cvs_rsh = "ssh"

Declare-x g_broken_filenames = "1"

Declare-x histsize = "1000"

Declare-x home = "/root"

Declare-x hostname = "server56.example.com"

Declare-x inputrc = "/etc/inputrc"

Declare-x lang = "zh_cn.gbk"

Declare-x lessopen = "|/usr/bin/lesspipe. sh % s"

Declare-x LOGNAME = "root"

Declare-x ls_colors = "NO = 00: fi = 00: di = 00; 34: Ln = 00; 36: Pi = 40; 33: So = 00; 35: BD = 40; 33; 01: Cd = 40; 33; 01: OR = 01; 05; 37; 41: MI = 01; 05; 37; 41: Ex = 00; 32 :*. cmd = 00; 32 :*. EXE = 00; 32 :*. COM = 00; 32 :*. BTM = 00; 32 :*. bat = 00; 32 :*. SH = 00; 32 :*. CSH = 00; 32 :*. tar = 00; 31 :*. tgz = 00; 31 :*. ARJ = 00; 31 :*. taz = 00; 31 :*. lzh = 00; 31 :*. zip = 00; 31 :*. z = 00; 31 :*. z = 00; 31 :*. gz = 00; 31 :*. bz2 = 00; 31 :*. bz = 00; 31 :*. TZ = 00; 31 :*. rpm = 00; 31 :*. cpio = 00; 31 :*. JPG = 00; 35 :*. GIF = 00; 35 :*. BMP = 00; 35 :*. xbm = 00; 35 :*. XPM = 00; 35 :*. PNG = 00; 35 :*. TIF = 00; 35 :"

Declare-x mail = "/var/spool/mail/root"

Declare-x oldpwd

Declare-x Path = "/usr/Kerberos/sbin:/usr/Kerberos/bin:/usr/local/sbin:/usr/local/bin:/sbin:/bin: /usr/sbin:/usr/bin:/root/bin"

Declare-x Pwd = "/root"

Declare-x shell = "/bin/bash"

Declare-x shlvl = "1"

Declare-x ssh_askpass = "/usr/libexec/OpenSSH/gnome-ssh-askpass"

Declare-x ssh_client = "192.168.0.211 49242 22"

Declare-x ssh_connection = "192.168.0.211 49242 192.168.0.156 22"

Declare-x ssh_tty = "/dev/pts/0"

Declare-x term = "xterm"

Declare-x user = "root"

Display: You can define which Desktop you are on

Histsize: Number of historical commands defined

Home: current home directory

PS1 base name

Env: displays the current variable.

Mainly used in characteristic Environments

 

Special variable: Bash

$? : Whether the previous command is successfully executed. 0 indicates successful, and 1-indicates different errors.

Location variable: $1: directly pass a variable to the script

$2, $3, more than 10, it is recommended to add {}

Arithmetic Operation echo "$ [$ A + $ B]"

"$ ($ A + $ B ))"

Bash command alias:

Alias is only valid for the moment

When the following command has spaces, it must be enclosed by quotation marks.

Alias cdnet = 'CD/etc/sysconfig/network-scripts'

Unalias Revocation

Global:/etc/profile,/etc/profile. d/*,/etc/bashrc

Local :~ /. Bash_profile ,~ /. Bashrc ,~ /. Bash_logout

Profile class:

It is usually used to set environment variables and run some commands to be executed during user logon.

Bashrc class:

Set the alias and local variables, only valid for the current Shell

Shell:

Interactive login shell: user login required <input type = "text"

Step 1: Read/etc/profile -->/etc/profile. d/> * --> ~ /. Bash --> ~ /. Bashrc -->/etc/bashrc

Non-interactive login shell: script shell that can be run without user logon

Log on first ~ /. Bashrc -->/etc/profile. d /*

Define alias declaration Variables

Source/etc/profile repeat this file

./Etc/profile re-reading this file is not recommended

\ Avoid Intention

Input/Output redirection

The default value is standard input/output.

Standard output device:/dev/stdout, 1 monitor,>

Error output:/dev/stderr, 2, monitor, 2>

Standard Input Device:/dev/stdin, 0 indicates standard input, keyboard, <

Merge output streams &>

> Overwrite output redirection> append output redirection 2> error message append redirection &> not append

Set-C force append to prohibit Overwrite

> | Force Overwrite

Ls/var>/tmp/var. out 2>/tmp/var. Err

Output stream

2> & 1 = &>

Pipeline: | used to connect commands. The output result of the previous command is treated as the input result of the next command.

Command | command

Tee separates input streams

Ls/etc | tee/tmp/LS. Out | less

The output of multiple commands must be saved to the same file.

Custom output redirection

0, 1, 2

Exec 3>/tmp/myout. Out defines a fixed File

Ls> & 3 overwrite fixed files

Exec 3> &-Undo

The input usage is the same as above.

&>/Dev/null: sets unwanted files to a data black hole.

>/Dev/null

Program execution flow:

Sequential execution

Select Branch

Loop execution: 1 +... + 100

For I in 1 2 3 4 5; do

Statement1

Statement2

Done

1 2 3 4 5 = 'seq 1 10'

= $ Seq 1 10 $

= {1 .. 10}

Text processing command:

The cut-D Delimiter is:

Cut-D:-F1 remove the first segment

Ifs: built-in line break

Ifs = $ '\ N'

Grep:

Grep, egrep, fgrep

Grep [Options] "pattern [mode]" File

Regular Expression: Basic regular expression, extended Regular Expression

Metacharacter re

Grep-I is case insensitive

-V is opposite to the default action. The matching result is not displayed.

-N: The matched row number is displayed in the text.

-A [after] n: the matching n rows are displayed.

-B [before] n

-C [] n context, displaying n rows online

-- Color: highlight matched items.

-E = egrep

^: Locates the first line of the line and matches the rivet.

$: Locate the end of a row

. Match a single character

*: Match the previous character 0 or any times

[]: Match any one of them

[X-y]

\ <

\>

\(..\)

$? : Execution result of the previous command

0: Execution successful

1-255: Failed

Short-circuit OPERATOR:

&&:

Command & command: execution after successful execution

|: After execution fails