Shell Variables

Shell Variables#

Shell variables are a general term. If you are using a specific shell, such as Bash, you can call it a Bash variable. But it is important to note that shell variables are not environment variables, do not be confused by their capitalization, here are the relevant official documents.

You can also view it by using the man command and searching for Shell Variables.

man bash

/Shell Variables

Common Shell Variables#

PS1#

Shell command prompt.

echo $PS1

\[\e]0;\u@\h: \w\a\]${debian_chroot:+($debian_chroot)}\[\033[01;32m\]\u@\h\[\033[00m\]:\[\033[01;34m\]\w\[\033[00m\]\$

UID#

Current user ID.

echo $UID

1000

PPID#

ps -fp $PPID

UID          PID    PPID  C STIME TTY          TIME CMD
kuga       46635   46570  0 10:56 ?        00:00:00 sshd: kuga@pts/0

You can see that the parent process of bash is sshd.

BASH_VERSION#

echo $BASH_VERSION

5.1.16(1)-release

BASH_SUBSHELL#

Subshell nesting level, starting from 0.

echo $BASH_SUBSHELL

0

SECONDS#

Seconds since the shell started.

echo $SECONDS

13963

RANDOM#

0 ~ 32767 random number.

echo $RANDOM

1024

Custom Shell Variables#

Refer to the later chapter on environment variables