Pipe and job control, shell variables, environment variable profiles

One, pipe and operation control

Pipe character |: To pass the output of a file to the following command
grep: A command used to filter a specified keyword
Application Examples:
[[email protected] ~]# ls |wc-l//list How many rows are in the current directory
8
[[email protected] ~]# Find/-type f//List all files in the current directory
./.bash_logout
./.bash_profile
./.BASHRC
./.CSHRC
./.TCSHRC
./.bash_history
./.ssh/known_hosts
./.ssh/authorized_keys
./anaconda-ks.cfg.1
./2.txt
./11.txt
./.lesshst
./1.txt
./1.txt.zip
./.viminfo
./3.txt
./4.txt
[[email protected] ~]# Find/-type f |wc-l//You can use the pipe to view the number of files
17

CTRL + Z shortcut key: Temporarily pause the current task
FG N Command (abbreviated to foreground foreground): Restarts the current task that was just paused, calls back, n represents the ID number, such as calling a process with a pause ID of 1, which can be invoked using #fg
Jobs: List the stopped tasks
BG n command (abbreviation for background background): Drop the task into the background and run, n represents the ID number, such as #bg 1, throw process 1 into the background and run
#sleep & command: Means to drop the Sleep 100 command into the background and run the command +& format
#ps aux |grep sleep//view sleep process

Second, shell variables

#env//View system built-in environment variables
#set//Not only to view the system built-in variables, but also to view user-defined variables
[Email protected] ~]# a=111//Custom environment variables, such as a=111
[Email protected] ~]# echo $a
111
#set |grep 111//Use the SET command to view a custom variable 111
Variable name rules: Letters, numbers, underscores, the first cannot be numbers

Variable values have special symbols that need to be enclosed in single quotes, for example: #a = ' A b C
[[email protected] ~]# a= ' a b C '
[Email protected] ~]# echo $a
A b C
‘
Accumulation of variables: for example, variable a b accumulates
[Email protected] ~]# a=1
[Email protected] ~]# b=2
[Email protected] ~]# echo $a $b
12

[[email protected] ~]# c= "A$BC"//Recognized as $BC
[Email protected] ~]# echo $c
A
[[email protected] ~]# c= "a$b" c//need to write $b and C separately, variable complex when using single or double quotation marks
[Email protected] ~]# echo $c
A2c

[[email protected] ~]# c=a "$b" c//assignment with complex variables enclosed in double quotes
[Email protected] ~]# echo $c
A2c

W command: View the user who is currently logged on to the system
[[Email protected] ~]# w//View the user who is currently logged on to the system
22:20:03 up min, 2 users, load average:0.00, 0.01, 0.06
USER TTY from [email protected] IDLE jcpu PCPU
Root pts/0 192.168.238.1 21:56 3.00s 0.22s 0.06s W
Root pts/1 192.168.238.1 22:19 6.00s 0.06s 0.06s-bash
[[email protected] ~]# echo $SSH _tty//To see which users are logged in
/dev/pts/0

Define global variables: formats such as: Export b=2
[[email protected] ~]# export hll=linux define global variables Hll=linux
[Email protected] ~]# echo $HLL
Linux
[[email protected] ~]# Bash//new open a child shell, directly run #bash,echo $hll or can output Linux, this is the global variable
[Email protected] ~]# echo $HLL
Linux

There is no Pstree command in the system, you can use the # yum install Psmisc #using Psmisc package for pstree installation

The Pstree command gives you a visual view of the directory structure, and you can see that Pstree is running in the new bash, Echo $hll, which is the same as the global variable, which takes effect down, and the parallel bash does not take effect.

unset custom variable name//Cancel custom variable
#bash//Enter a new sub-shell

III. environment variable configuration file

environment variable configuration file/etc/profile and/ETC/BASHRC belong to the system level, generally do not modify;
Can modify the user's home directory ~/.BASHRC ~/.bash_profile These belong to the user level, can be set to a single user

[Email protected] ~]# vim. Bash_profile//Editor home directory. Bash_profile
[[email protected] ~]# source. Bash_profile or #. Bash_profile//After editing, you need to have the configuration file take effect immediately, you can use source or. , here. As with the source effect, the configuration file configuration is loaded

In the ~/.bash_logout file, you can define a command history that allows a user to exit the login, and a command to delete the history command in this configuration file

About PS1
The PS1 can be
[[Email protected] ~]//From left to right, followed by the current user, @, hostname, current directory
[Email protected] ~]# cd/etc/sysconfig/network-scripts/
[Email protected] network-scripts]# echo $PS 1
[\[email protected]\h \w]\$//\u is user,\h is hostname,\w is the current directory
#PS1 = ' [\[email protected]\h \w]\$ '//If w is changed to lowercase w then it will display an absolute path
Instance:
[[email protected] network-scripts]# ps1= ' [\[email protected]\h \w]\$ '//change W to lowercase W
[[Email protected]/etc/sysconfig/network-scripts]#//will be displayed as an absolute path

[[email protected]/etc/sysconfig/network-scripts] #PS1 = ' <\[email protected]\h \w> \$ '//Can be modified [] for < >
<[email protected]/etc/sysconfig/network-scripts> #//after modification [] it becomes <>
$ sign, root user is #, other normal user is $
[[email protected] network-scripts] #PS1 = ' [\033[01;32m]\[email protected]\h[\033[00m]:[\033[01; 36m]\w[033[00m]\$] ' Modify Color

PS2: Enter MySQL to enter the small terminal of MySQL, into the PS2
[[email protected] network-scripts] #echo $PS 2

Pipe and job control, shell variables, environment variable profiles