A description of some of the common environment variables and parameter variables in the shell script and examples of simple shell scripts

Environment Variables

1. $HOME
   Home directory of the current user
   
   
2. $PATH
   A colon-delimited list of directories to search for commands
   
   
3. $PS 1
   A command prompt, usually a $ character, but in bash, you can use some more complex values. For example, the string [\[email protected]\h\w]$ is a popular default value that gives the user name/machine name and the current directory name, and of course a $ prompt.
   
   
4. $PS 2
   A second-level prompt that represents the subsequent input, usually the > character.
   
   
5. $IFS
   Enter the domain delimiter. When the shell reads the input, it gives a set of characters used to separate the words, usually spaces, tabs, and line breaks.
   
   
6. $
   The name of the shell script
   
   
7. $#
   The number of arguments passed to the script
   
   
8. $$
   The process number of the shell script, which is typically used by the script to generate a unique temporary file, such as/temp/tmpfile_$$
   
   

parameter Variables

1. $, $, ...
   Parameters of the script program
   
   
2. $*
   All parameters are listed in a variable, separated by the first character in the environment variable IFS. If IFS is modified, the way $* separates the command line as a parameter will change.
   
   
3. [Email protected]
   It is an ingenious variant of $*, which does not use IFS environment variables, so even if IFS is empty, the parameters will not be squeezed together.
   
   

Shell Script Example

#!/bin/shsalutation= "Hello" Echo $salutationset foo bar Bamecho "The program was now running" echo "the second parameter W As $ "echo" the first parameter was $ "echo" The parameter list was $* "echo" The user's home directory is $HOME "echo" plea Se Enter a new greeting "read Salutationecho $salutationecho" The script is complete "exit 0<span style=" color: #cc0000; " ></span>

Test Results

The script creates the variable and displays its contents, then displays various parameter variables and the environment variable $home are already present and have the appropriate values.

A description of some of the common environment variables and parameter variables in the shell script and examples of simple shell scripts