Syntax knowledge of shell scripts--Process Control

①if-elif-elif-else-fi

If-fi

' if ($a >); then echo $a; fi ' or ' if [$a-gt];then echo $a; Fi '

If-else-fi

' if ($a =), then echo $a; else echo 30;fi ' or ' if [$a-eq];then echo $a; else echo 30;fi '

If-elif-elif-else-fi

' if ($a >) && (($a =)); then echo $a; elif (($a > 20)) | | ($a =); then echo $[$a +1];else echo ' Sorry '; Fi '

Note: If you enclose the condition in square brackets [], there must be a space between the if and the [,] operand and [,]
> * * * *-gt = * *-EQ >= * * *-ge <= * *-le < * * * * * *-LT

If Judge document properties

' If [-defrwx filename] '-D exists && directory-E exists-F exists && normal file-R readable-W writable-X Executable

②case $a in value1) command;; value2) command;; VALUE3) command;; *) command; Esac

' Read-p ' please input a number: ' A;

Case $[$a%2] in

0)

echo "The number is even!";;

1)

echo "The number is odd!";;

*)

echo "This is impossible!";;

Esac '

③for Cycle

For variable name in loop condition; do command[;] Done

eg

A= ' seq 1 10 ';

For i in $a;d o echo $i;d One or for i in ' seq 1 ';d o echo $i;d One or for I in 1 2 3 4 5;do echo $i;d One

Note: ' seq a b ' denotes a sequence from a to B, e.g. ' SEQ 1 10 ' generates a sequence from 1 to 10

④while Cycle

　　　　while condition; do Command;done

eg

a=10;

While [$a-ge 1];d o

echo $a;

A=$[$-1];

Done

Syntax knowledge of shell scripts--Process Control