Shell Scripting Practices

1. The script determines whether the command output is empty

(1) Determine if the string is empty

If ["$str" = ""]
If [x "$str" = x]
If [-Z ' $str '] (-n is not null)
Note: You have to double quotation marks, or some commands will be error, form a good habit!

2. Enter y/n

You can use the judgment symbol for data judgment, such as checking if a variable is empty [-Z $SHELL], and note that the components within the brackets ("[]") must be separated by a space. The following script is available:

#!/bin/bashread-p "Input You Choice (y/n):" choice["$choice" = = "Y"] | | ["$choice" = = "Y"] && echo "Ok,continue" && exit 0["$choice" = = "n"] | | ["$choice" = = "N"] && echo "oh,interrupt!" && exit 0echo "I don ' t know what's your choice" && E XIT 0

#! /bin/shecho "Is it morning? Please answer yes or No. " Read Yes_or_noif ["$YES _or_no" = "YES"]; Then  echo "Good morning!" elif ["$YES _or_no" = "NO"]; Then  echo "Good afternoon!" else  echo "Sorry, $YES _or_no not recognized. Enter yes or No. "  Exit 1fiexit 0

　　

(3) While condition loop

Similar to the C language. Like a script that validates the password: #! /bin/shecho "Enter password:" Read trywhile ["$TRY"! = "secret"]; Do  echo "Sorry, try again"  Read Trydone The following example controls the number of cycles by arithmetic operations: #!/bin/shcounter=1while ["$COUNTER"-lt];  do echo "Here's Go Again"  counter=$ (($COUNTER + 1)) done

(3) Case and while combination

#!/bin/bashwhile:                                   : True, always loop                                        do the command to loop execution        echo-n "Enter any number [1-5]:" Enter the ordinal 1-5        read Nu                            Set the read variable case        $nu in                        to select, enter if 1-5 of the number        1|2|3|4|5)                echo "Enter Anumber 1 and 5" on the loop this line, let you keep the input 1-5                ;;        *)                                   If you enter a number that is not 1-5                echo-n "wrong numbers, continue (y/n?:)"   Ask if you continue                read con                     setting read variable case                $con in                 make a selection to see if it is y|yes| y| Yes these few                y|yes| y| Yes)                        continue              If yes, then skip and let you re-enter, if not                        ;                *)                             then execute this break exit loop break                        ;;                Esac        Esacdone

　

　　

Shell Scripting Practices