Shell Introduction, Command history, command completion and aliases, wildcard characters, input and output redirection

Shell Introduction

• The shell is a command interpreter that provides interaction between the user and the machine
• Supports specific syntax, such as logical judgment, looping
• Each user can have their own specific shell
• CentOS7 default shell is bash (Bourne Agin Shell)
• and Zsh,ksh and so on.

Command history

• Maximum Deposit 1000.

• Variable Histsize modified in/etc/profile

  vi /etc/profile找到HOSTNAME=`/usr/bin/hostname 2>/dev/null`HISTSIZE=1000if [ "$HISTCONTROL" = "ignorespace" ] ; then如果觉得1000条不够可以改成5000

After the change, you must exit the terminal to re-enter or source/etc/profile change

• Variable Value re-assignment

histtimeformat= "%y/%m/%d%h:%m:%s"

[[email protected] ~]# history     1  ls    2  ls /etc/passwd    3  cat /etc/passwd    4  [[email protected] ~]# cat /etc/passwd    5  root:x:0:0:root:/root:/bin/bash    6  bin:x:1:1:bin:/bin:/sbin/nologin    7  daemon:x:2:2:daemon:/sbin:/sbin/nologin    8  adm:x:3:4:adm:/var/adm:/sbin/nologin    9  lp:x:4:7:lp:/var/spool/lpd:/sbin/nologin

After the value is re-assigned

[[email protected] ~]# HISTTIMEFORMAT="%Y/%m/%d %H:%M:%S "[[email protected] ~]# history     1  2017/08/30 19:20:18 ls    2  2017/08/30 19:20:18 ls /etc/passwd    3  2017/08/30 19:20:18 cat /etc/passwd    4  2017/08/30 19:20:18 [[email protected] ~]# cat /etc/passwd    5  2017/08/30 19:20:18 root:x:0:0:root:/root:/bin/bash    6  2017/08/30 19:20:18 bin:x:1:1:bin:/bin:/sbin/nologin    7  2017/08/30 19:20:18 daemon:x:2:2:daemon:/sbin:/sbin/nologin    8  2017/08/30 19:20:18 adm:x:3:4:adm:/var/adm:/sbin/nologin

Then open a new terminal, this environment variable is not in effect.

If you want this environment variable to take effect globally, you need to edit/etc/profile to add histtimeformat= "%y/%m/%d%h:%m:%s" to the inside

fiHOSTNAME=`/usr/bin/hostname 2>/dev/null`HISTSIZE=5000HISTTIMEFORMAT="%Y/%m/%d %H:%M:%S"if [ "$HISTCONTROL" = "ignorespace" ] ; then    export HISTCONTROL=ignoreboth

Effective after Source/etc/profile

• Permanently save command history

  Chattr +a ~/.bash_history

Can only append cannot delete

• If you do not exit normally, the history command is not fully saved
• !!

  Represents running the last history command

• !n

  Specify the number of Run history rows command

• ! command

  Represents the last command in command history to enter this command

Command completion and aliases

• tab, knock, Knock, double click.
• CENTOS7 support parameter completion, the default is not, you need to install Yum install-y bash-completion after restarting the system to take effect.
• Alias aliases, give the command a new name

Alias exists in the. bashrc file in the user's home directory.

There are still some/etc/profile.d/below

Unalias to cancel a custom alias

Wildcard characters *

[[email protected] ~]# ls111  1eer  1.txt  2.txt  anaconda-ks.cfg  erwe[[email protected] ~]# ls *.txt1.txt  2.txt[[email protected] ~]# [[email protected] ~]# ls 1*1eer  1.txt111:[[email protected] ~]# ls *1*1eer  

?

Question mark denotes any one character

[[email protected] ~]# ls ?.txt1.txt  2.txt[[email protected] ~]# ls *.txt1.txt  2.txt  bbcc.txt  

[]

Select Range

[[email protected] ~]# ls [123].txt1.txt  2.txt[[email protected] ~]# ls [0-9].txt1.txt  

{}

It's also a choice, similar to [], but with a comma in the middle.

[[email protected] ~]# ls {1,2}.txt1.txt  

Input/Output redirection >

Remove the content from the > front to redirect to the back content.

>>

Append the contents of the >> front to the following content.

2>

Indicates that the information for the run error is directed to a file

[[email protected] ~]# fddd-bash: fddd: 未找到命令[[email protected] ~]# fddd 2> 1.txt [[email protected] ~]# cat 1.txt -bash: fddd: 未找到命令

2>>

Error Append redirect

&>

Error and correct output redirection

<

Input redirect

Enter the contents of the < right side of the file into the < left command.

Shell Introduction, Command history, command completion and aliases, wildcard characters, input and output redirection