Linux shell basic programming 2, linuxshell BASIC Programming

Linux shell basic programming 2, linuxshell BASIC Programming

While Loop

Syntax 1:

While [condition]

Do

Command Sequence

Done

Syntax 2:

While read-r line

Do

Command Sequence

Done

(Remember that while and left brackets must have spaces)

Example

1 #!/bin/bash2 j=13 SUM=04 while [ $j -lt 10 ]5 do6 SUM=$((SUM+j))7 j=$[j+1]8 done9 echo $SUM

 

If judgment statement

Syntax 1:

If condition

Then

Command Sequence

Fi

Syntax 2:

If condition

Then

Conditional Sequence

Else

Conditional Sequence

Fi

Syntax 3:

If condition

Then

Conditional Sequence

Elif Condition

Then

Conditional Sequence

Elif Condition

Then

Conditional Sequence

Else

Conditional Sequence

Fi

Example

#!/bin/bashif  [ -d /tmp/123 ];thenecho "this is directory"else echo "this is not directory"fi

　　

Case statement

Syntax 1:

Case $ variable name in

Condition 1)

Command Sequence

;;

Condition 2)

Command Sequence

;;

Condition 3)

Command Sequence

;;

*)

Command Sequence

Esac

Syntax 2:

Case $ variable name in

Condition 1 | Condition 4)

Command Sequence

;;

Condition 2 | condition 5)

Command Sequence

;;

Condition 3 | Condition 6)

Command Sequence

;;

*)

Command Sequence

Esac

 1 #!/bin/bash 2 case $1 in  3 top) 4     top 5     ;; 6 free) 7     free 8     ;; 9 df)10     df11      ;;12 *)13     echo "no param"14 esac

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Function Definition:

Syntax 1:

Method Name (){

Command Sequence

}

Syntax 2:

Function Method Name {

Command Sequence

}

1 #!/bin/bash2 sum(){3   echo $(($1+$2))4 }5 sum 5 6