Detailed explanation of PS1, PS2, PS3, PS4 variables under Linux

In the Linux system, PS1 , PS2 , PS3 and PS4 are specific environment variables , each of them plays a different role in controlling prompts and menu prompt information.

These PS variables can provide users with a flexible way to customize and control the appearance and behavior of the command line in the Linux system, thereby improving the user's interactive experience with the system.

Note:

If you want to permanently modify the prompt for a long time, you can add the command to modify the prompt to the $HOME/.bashrc or $HOME/.bash_profile file.

1, PS1 variable It is mainly used to set up the shell command prompt. Whenever you enter a command in the terminal, the string displayed is controlled by the PS1 variable.

You can customize the value of the PS1 variable according to your own preferences and needs, thereby changing the appearance and format of the command prompt.

The default value is: [u@h W]$, which means: display the user's host name working directory, you can enter the echo $PS1 command in the terminal window to view:

[root@iSCSI-server ~]# echo $PS1 [u@h W]$ [root@iSCSI-server ~] #The above is explained in detail as follows

character stands for meaning Remark [ represent[ u Represents the current user root @ represent@ h stands for host name iSCSI-server represents spaces (not displayed) W represents the current directory name ~ represents the current user’s home directory ] represent] $ stands for privileged user or ordinary user, ordinary user $ space, super user # space PS1 Variable parameters available

parameter describe d represents the date, the format is weekday month date H Full host name. h Only take the first name of the host t The display time is in 24-hour format, such as: HH:MM:SS T Display time in 12-hour format A The display time is in 24-hour format: HH:MM u Current user’s account name v BASH version information w Full working directory name. The home directory will be replaced by ~ W Use basename to get the working directory name, so only the last directory will be listed #What order was issued $ Prompt character, if it is root, the prompt is: #, for ordinary users: $ [ character"[" ] character"]" ! Command line dynamic statistics of historical command times PS1 variable usage examples

1. Simple prompt

[root@iSCSI-server ~]# PS1='u@h:w$ ' root@iSCSI-server:~$

This prompt will display the username ( u ), hostname ( h ), current working directory ( w ), and a dollar sign ( $ ).

It is suitable for users who prefer simple and straightforward prompts.

2. Display the complete path

[root@iSCSI-server ~]# PS1='[u@h w]# ' [root@iSCSI-server ~]# cd /var/log [root@iSCSI-server /var/log]# pwd /var/log [root@iSCSI-server /var/log] #Displays the full path of the current working directory ( w ), which is useful for quickly identifying the current location when working in deep directories.

3. Display time and date

[root@iSCSI-server ~]# PS1='[d]u@h w$ ' [Wed March 20]root@iSCSI-server ~$

[root@iSCSI-server ~]# PS1='[t] [u@h w]# ' [09:27:06] [root@iSCSI-server ~]# [09:27:11] [root@iSCSI-server ~]# or: [root@iSCSI-server ~]# PS1='(`date "%H:%M:%S"`)[u@h W]$ ' (09:43:59)[root@iSCSI-server ~]# (09:44:01)[root@iSCSI-server ~] #4. Color prompt

[root@iSCSI-server ~]# PS1="[e[33;1m]u[e[31;1m]@[e[33;1m]h [e[36;1m]w[e[ 34;1m]$ [e[0m]" root@iSCSI-server ~$ root@iSCSI-server ~$

Color code format: ** [e[F;Bm] **

Among them: F represents the font color, B represents the background color, the details are as follows:

Font code Background code color 30 40 black 31 41 red 32 42 green 33 43 yellow 34 44 blue 35 45 purple 36 46 cyan 37 47 White 2, PS2 variable This is the second prompt, used to display information when connecting multiple lines of one command in the interactive shell .

When your command line input is longer than one line, the system will use the PS2 prompt to continue input.

This allows users to easily enter long commands in multiple lines, improving the efficiency of command line operations.

A very long command can be displayed on separate lines by adding at the end PS2 The default prompt for multi-line commands, the default value is > #Modify the prompt from > to >

[root@iSCSI-server ~]# echo > 1 1 3, PS3 variable This environment variable is used to control the menu prompt information created by the select command.

In Linux , the select command allows the user to select one from a series of options, while the PS3 variable is responsible for defining the prompts displayed during the selection process symbol.

By customizing PS3 , you can make the menu prompts of the select command more suitable for your needs.

Do not use PS3 variables

[root@iSCSI-server ~]# cat myps3.sh #!/bin/bash

echo "Here are some options, please choose the one you want:" select option in "Option 1" "Option 2" "Exit"; do case $option in "Option 1") echo "You selected option 1" break ;; "Option 2") echo "You selected option 2" break ;; "quit") echo "Exit script" exit 0 ;; *) echo "Invalid selection, please select again" ;; esac done Run sh script:

[root@iSCSI-server ~]# bash myps3.sh Here are some options, please choose the one you want: 1) Option 1 2) Option 2 3) Exit #? 1 You selected option 1 [root@iSCSI-server ~] #Use PS3 variables

First define PS3 variables in the above script:

#!/bin/bash

# Set PS3 variables to customize the prompt for the select command # PS3="Please select an option: "

echo "Here are some options, please choose the one you want:" select option in "Option 1" "Option 2" "Exit"; do case $option in "Option 1") echo "You selected option 1" break ;; "Option 2") echo "You selected option 2" break ;; "quit") echo "Exit script" exit 0 ;; *) echo "Invalid selection, please select again" ;; esac done Then run the script:

[root@iSCSI-server ~]# bash myps3.sh Here are some options, please choose the one you want: 1) Option 1 2) Option 2 3) Exit Please select an option: 1 You selected option 1 [root@iSCSI-server ~] #4, PS4 variable set -x is used to modify the prefix of the tracking output. This variable is rarely used.

Detailed explanation of PS1, PS2, PS3, PS4 variables under Linux

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