, we constructed some simple menus and built the logic used to act on a user’s selection. To do this, we used a series of if commands to identify which of the possible choices had been selected. This type of construct appears frequently in programs, so much so that many programming languages (including the shell) provide a flow-control mechanism for multiple-choice decisions., we see the logic used to act on a user’s selection shows some valid patterns.Table 31-1. case Pattern Examples
Pattern
Description
a)
Matches if word equals a.
[[:alpha:]])
Matches if word is a single alphabetic character.
???)
Matches if word is exactly three characters long.
*.txt)
Matches if word ends with the characters .txt.
*)
Matches any value of word. It is good practice to include this as the last pattern in a case command to catch any values of word that did not match a previous pattern; that is, to catch any possible invalid values.
Table 31-1. case Pattern Examples
Pattern | Description |
|---|---|
| Matches if |
| Matches if |
| Matches if |
| Matches if |
| Matches any value of |
Here is an example of patterns at work:
#!/bin/bash read -p "enter word > " case $REPLY in [[:alpha:]]) echo "is a single alphabetic character." ;; [ABC][0-9]) echo "is A, B, or C followed by a digit." ;; ???) echo "is three characters long." ;; *.txt) echo "is a word ending in '.txt'" ;; *) echo "is something else." ;; esac
It is also possible to combine multiple patterns using the vertical pipe character as a separator. This creates an “or” conditional pattern. This is useful for such things as handling both upper- and lowercase characters. For example:
#!/bin/bash # case-menu: a menu driven system information program clear echo " Please Select:A.Display System InformationB.Display Disk SpaceC.Display Home Space UtilizationQ.Quit " read -p "Enter selection[A, B, C or Q]> " case $REPLY inq|Q)echo "Program terminated." exit ;;a|A)echo "Hostname: $HOSTNAME" uptime ;;b|B)df -h ;;c|C)if [[ $(id -u) -eq 0 ]]; then echo "Home Space Utilization (All Users)" du -sh /home/* else echo "Home Space Utilization ($USER)" du -sh $HOME fi ;; *) echo "Invalid entry" >&2 exit 1 ;; esac
Here, we modify the case-menu program to use letters instead of digits for menu selection. Notice that the new patterns allow for entry of both upper- and lowercase letters.
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