This article is the (thirteenth) part of the Linux Shell Scripting Series . For more Linux Shell tutorials, please see: Linux Shell Scripting Series Tutorials
After the last article , branch statements are very practical. Basically, high-level languages support branch statements (python does not). Most of them use the switch … case format, but there is no switch … case in Shell, but don’t worry, Shell supports branch statements. Yes, but using the case ... esac format. Both are essentially the same.
1. Shell branch statement case esac syntax
case value in
Mode 1)
command1
command2
command3
;;
Mode 2)
command1
command2
command3
;;
*)
command1
command2
command3
;;
esac
Description: The case is followed by the value, the value is followed by the keyword in, followed by various matching patterns, each pattern must end with a closing parenthesis.
Values can be variables or constants.
The pattern supports regular expressions and can use the following characters:
* any string ? any character [abc] one of the three characters a, b, or c [an] any character from a to n | Multiple selection
After the match finds that the value matches a certain pattern, all commands during the period start to be executed until ;;.
;; Similar to break in other languages, it means skip to the end of the entire case statement without executing the following statement.
*) is similar to default, if there is no matching pattern above, the content in *) is executed.
2. Shell branch statement case...esac usage example
Learn the case...esac command with an example:
#!/bin/sh
#auther:linuxdaxue.com
#date:2016-05-30
case $1 in
start | begin)
echo "I am started!"
;;
stop | end)
echo "I am stopped!"
;;
*)
echo "Other command!"
;;
esac
Description: This script exercises pattern matching. Pattern matching supports the '|' character. If a condition is met, the command will be executed.
output:
$./test.sh start I am started! $./test.sh stop I am stopped! $./test.sh begin I am started! $/test.sh hello Other command!
Next, I will show you an example of generating a menu through the case...esac statement:
#!/bin/bash #Author:linuxdaxue.com #Date:2016-05-30 #Desc: Shell case menu exercise clear # Clear the screen. echo " Contact List" echo " ------- ----" echo "Choose one of the following persons:" echo echo "[E]vans, Roland" echo "[J]ones, Mildred" echo "[S]mith, Julie" echo "[Z]ane, Morris" echo read person case "$person" in # Note that variables are referenced by "". "E" | "e" ) # Accept uppercase or lowercase input. echo echo "Roland Evans" echo "4321 Floppy Dr." echo "Hardscrabble, CO 80753" echo "(303) 734-9874" echo "(303) 734-9892 fax" echo "[email protected]" echo "Business partner & old friend" ;; # Note that every option must end with a double semicolon ;;. "J" | "j" ) echo echo "Mildred Jones" echo "249 E. 7th St., Apt. 19" echo "New York, NY 10009" echo "(212) 533-2814" echo "(212) 533-9972 fax" echo "[email protected]" echo "Ex-girlfriend" echo "Birthday: Feb. 11" ;; # The following information about Smith and Zane is omitted here. * ) # Default options. # Empty input (enter RETURN), also works here. echo echo "Not yet in database." ;; esac echo # practise: # ----- # Modify this script to accept multiple inputs, #+ and can display multiple addresses. exit 0
Description: This example mainly demonstrates how to use the case...esac statement to generate the menu, so that everyone can learn the usage of the case...esac statement more vividly and flexibly.
output:
Contact List
------- ----
Choose one of the following persons:
[E]vans, Roland
[J]ones, Mildred
[S]mith, Julie
[Z] ane, Morris
E
Roland Evans
4321 Floppy Dr.
Hardscrabble, CO 80753
(303) 734-9874
(303) 734-9892 fax
[email protected]
Business partner & old friend
The above is the output of the input E parameter, input S or Z, the output will be as follows:
Contact List
------- ----
Choose one of the following persons:
[E]vans, Roland
[J]ones, Mildred
[S]mith, Julie
[Z] ane, Morris
WITH
Not yet in database.
Well, let's introduce the usage of branch statement case...esac in Shell first. case...esac is a very powerful command, and you can use it to do a lot of things. This article is just for introductory purposes. More needs everyone to try and practice a lot in actual use.
For more Linux Shell tutorials, please see: Linux Shell Scripting Series Tutorials
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This article is transferred from: Linux Shell Scripting Tutorial Series (13) Shell branch statement case ... esac tutorial