Pipe and job control, shell variables, environment variable configuration files

Pipe character and job control

• | Give the result of the previous command to the following command processing.

  [[email protected] ~]# cat 1.txt |wc -l  统计行数5[[email protected] ~]# cat 1.txt |grep ‘aaa‘aaaa   剪切出aaa的行

• CTRL Z pauses a task, which can only be operated at the current terminal, and the other terminal will be able to check the process
• Jobs view the tasks in the background
• BG [ID] The task to the background, no ID default last
• FG [ID] The task to the foreground, no ID default last
• command to add & drop directly into the background,

  [[email protected] ~]# sleep 200    暂停200秒^Z[1]+  已停止               sleep 200[[email protected] ~]# jobs[1]+  已停止               sleep 200[[email protected] ~]# fg 1sleep 200[[email protected] ~]# bg 1[1]+ sleep 200 &[[email protected] ~]# jobs[1]+  运行中               sleep 200 &[[email protected] ~]# [[email protected] ~]# sleep 100 &[1] 2213[[email protected] ~]# jobs[1]+  运行中               sleep 100 &

Shell variables

• Path,home,pwd,logname are all variables.
• EVN command displays the environment variables of the system
• The set command not only can view the environment variables of the system, but also can view the user-defined variables, many of which are set |less to see more convenient
• Custom variable: a=111

  [[email protected] ~]# a=111[[email protected] ~]# echo $a111[[email protected] ~]# set |grep 111_=111a=111

• Rules for variable names: letters, numbers, underscores, numbers cannot be the first

  [[email protected] ~]# a1=1[[email protected] ~]# a_1=2[[email protected] ~]# 1a=3-bash: 1a=3: 未找到命令

• The value of a variable must be enclosed in single quotation marks when it has a special symbol, not double quotes, and some special symbols cannot be used.

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

• The sum of the variables, if one variable refers to another variable, enclose the double quotation mark, cannot add the single quotation mark.

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

• Global variables Export a=12 set a global variable, just down the sub-shell copy down, in its upper level shell and other terminals do not take effect, script 1 inside the nested script 2,2 can use the variables inside 1

  [[email protected] ~]# w09:41:58 up 57 min,  1 user,  load average: 0.00, 0.01, 0.05USER     TTY      FROM             [email protected]   IDLE   JCPU   PCPU WHATroot     pts/0    192.168.16.1     08:48    6.00s  0.62s  0.16s w[[email protected] ~]# echo $SSH_TTY 查看自己的登录TTY/dev/pts/0pstree命令以树状图的方式展现进程之间的派生关系，显示效果比较直观

• Unset variable name---cancel variable

environment variable configuration file

• /etc/profile user Environment variables, interaction, login to execute, this is a system-level global variable
• /ETC/BASHRC the user does not need to log in, executes the shell to be effective, usually does not edit
• ~/.bash_profile there is a need to edit the user's own environment variables
• source. Bash_profile make its changes effective
• ~/.bashrc
• The. Bash_profile startup invokes the. BASHRC,.BASHRC calls the system's BASHRC
• To configure environment variables, the most insurance is written in the. bashrc file. Because the file will always be called, whether it be landed or not!
• ~/.bash_history User's command history file
• ~/.bash_logout allows the user to delete the command history each time they exit the command can be added to this file
• Ps1= ' [[\033[01;32m]\[email protected]\h[\033[00m]:[\033[01;36m]\w[\033[00m]]\$ ' with color display settings command input to the left to display information, PS2 settings into other terminal display such as MySQL command input effect display

  [[email protected] ~]# echo $PS1[\[email protected]\h \W]\$u显示登录的用户，h显示登录的机器名，W显示当前目录名，$显示用户级别普通用户显示$root用户显示#[[email protected]]$PS1=‘[\[email protected]\h \w]\$‘[[email protected] /etc/sysctl.d]#

Extended

• Bash_profile and BASHRC differences
• Simple Audit system
• About the meaning of Prompt_command environment variables

Pipe and job control, shell variables, environment variable configuration files