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Pipe symbol, Job control

1. Pipe symbol | : Outputs a command to the following command execution

[[email protected] ~]# ls111  1.txt   2_hard.txt  2.txt.bak.bak  4.txt              apr-1.4.5123  1.txt~  2_soft.txt  3.txt          anaconda-ks.cfg.1  apr-1.4.5.tar.gz[[email protected] ~]# ls | wc -l12

2.ctrl+z: Pause execution of the command:

[[email protected] ~]# vim 1.txt[1]+  已停止               vim 1.txt

3. Use command FG to continue execution of the paused command: Put the command to the foreground

[[email protected] ~]# fgvim 1.txt

4.jobs command: Lists the stopped commands to

[[email protected] ~]# jobs[1]-  已停止               vim aa.txt[2]+  已停止               vim 1.txt

5.bg: Move the command to the background to continue running
6.sleep time: How long is it suspended?
7. Add & to the command, and put the command directly in the background to execute.

Shell variables

1.ENV: View System Variables

[[email protected] ~]# envXDG_SESSION_ID=1HOSTNAME=weix-01SELINUX_ROLE_REQUESTED=TERM=xtermSHELL=/bin/bashHISTSIZE=1000SSH_CLIENT=192.168.127.1 53879 22SELINUX_USE_CURRENT_RANGE=SSH_TTY=/dev/pts/0USER=root

The 2.set command can view system variables as well as user-defined variables:

[[email protected] ~]# setBASH=/bin/bashBASHOPTS=checkwinsize:cmdhist:expand_aliases:extquote:force_fignore:histappend:hostcomplete:interactive_comments:login_shell:progcomp:promptvars:sourcepathBASH_ALIASES=()BASH_ARGC=()BASH_ARGV=()BASH_CMDS=()BASH_LINENO=()BASH_SOURCE=()BASH_VERSINFO=([0]="4" [1]="2" [2]="46" [3]="2" [4]="release" [5]="x86_64-redhat-linux-gnu")BASH_VERSION=‘4.2.46(2)-release‘COLUMNS=80DIRSTACK=()EUID=0GROUPS=()

3. Variable naming rules: Alphanumeric underline, the first cannot be a number

[[email protected] ~]# a1=2[[email protected] ~]# echo $a12[[email protected] ~]# a_1=3[[email protected] ~]# echo $a_13[[email protected] ~]# _a1=4[[email protected] ~]# echo $_a14[[email protected] ~]# 1aa=5-bash: 1aa=5: 未找到命令

4. When the variable value has a special symbol, it needs to be expanded with single quotation marks.

[[email protected] ~]# a=a b c-bash: b: 未找到命令[[email protected] ~]# a=‘a b c‘

Double quotes may not display correctly:

[[email protected] ~]# a="a$bc"[[email protected] ~]# echo $aa[[email protected] ~]# a=‘a$bc‘[[email protected] ~]# echo $aa$bc

5. Variable overlay: Multiple variable overlays can be caused by double quotation marks

[[email protected] ~]# a=1[[email protected] ~]# b=2[[email protected] ~]# echo $a$b12[[email protected] ~]# a=‘a$bc‘[[email protected] ~]# echo $a$ba$bc2[[email protected] ~]# c="a$bc"[[email protected] ~]# c="a$b"c[[email protected] ~]# echo $ca2c

6. Define variables as local variables directly on one terminal, not valid on other terminals
7. Define global variables: export, for a shell below the sshd in a backward-compatible global, cannot upward

[[email protected] ~]# export weix=linux[[email protected] ~]# echo $weixlinux[[email protected] ~]# bash[[email protected] ~]# echo $weixlinux

8.pstree: Can see under which bash

[[email protected] ~]# pstreesystemd─┬─NetworkManager───2*[{NetworkManager}]        ├─VGAuthService        ├─agetty        ├─auditd───{auditd}        ├─chronyd        ├─crond        ├─dbus-daemon───{dbus-daemon}        ├─firewalld───{firewalld}        ├─lvmetad        ├─master─┬─pickup        │        └─qmgr        ├─polkitd───5*[{polkitd}]        ├─rsyslogd───2*[{rsyslogd}]        ├─sshd───sshd───bash───bash───pstree        ├─systemd-journal        ├─systemd-logind        ├─systemd-udevd        ├─tuned───4*[{tuned}]        └─vmtoolsd───{vmtoolsd}

9. Cancel Assignment: unset

[[email protected] ~]# echo $weixlinux[[email protected] ~]# unset weix[[email protected] ~]# echo $weix

environment variable configuration file

1.profile: User login is automatically loaded
2.BASHRC: Execute shell script to load automatically without login
3.bash-logout: Defines what needs to be done when a user exits

4. PS1: Changing the display

   [[email protected] ~]# PS1=‘[\[email protected]\h \w]\$‘[[email protected] ~]#ls111    1.txt~      2.txt.bak.bak  aa.txt             apr-1.4.5.tar.gz123    2_hard.txt  3.txt          anaconda-ks.cfg.11.txt  2_soft.txt  4.txt          apr-1.4.5[[email protected] ~]#cd /etc/Display all 186 possibilities? (y or n)[[email protected] ~]#cd /etc/                    [[email protected] /etc]#cd /root/123[[email protected] ~/123]#PS1=‘[\[email protected]\h \W]\$‘            #大写W，显示相对路径[[email protected] 123]#cd                            #小写w显示绝对路径

Shell Foundation (middle)