Most Common UNIX Commands Part - V

Lets see about some more loop statements which can be used in unix shell scripting

while: while followed by condition then set of statements to be executed do,done act as flower braces

Syntax: while [condition/statement]
             do
             statement 1
             statement 2
             :
             :
              statement n
              done

 eg:

#!/bin/sh
a=0
while [ $a -lt 10 ]
do
   echo $a
   a=`expr $a + 1`
done

Output will be as follows

0
1
2
3
4
5
6
7
8
9

Until: This command functionality is viceversa of while command. In while the loops continues to execute when condition is true , but in until the loops continues to execute until the condition is false.

Syntax: until [condition/statement]
             do
             statement 1
             statement 2
             :
             :
              statement n
              done

eg:

#!/bin/sh
a=0
until [ ! $a -lt 10 ]
do
   echo $a
   a=`expr $a + 1`
done

output will be as follows

0
1
2
3
4
5
6
7
8
9

Hope this helps you in understanding unix loop commands