While loop

Shell Script While Loop Examples

by Vivek Gite · 6 comments

Can you provide me a while loop control flow statement shell script syntax and example that allows code to be executed repeatedly based on a given boolean condition?

Each while loop consists of a set of commands and a condition. The general syntax as follows for bash while loop:

while [ condition ]
do
 command1
 command2
 commandN
done

1. The condition is evaluated, and if the condition is true, the command1,2…N is executed.
2. This repeats until the condition becomes false.
3. The condition can be integer ($i <>

ksh while loop syntax:

while [[ condition ]] ; do
 command1
 command1
 commandN
done
 

csh while loop syntax:

     while ( condition )
        commands
    end
 

BASH while Loop Example

#!/bin/bash
c=1
while [ $c -le 5 ]
do
 echo "Welcone $c times"
 (( c++ ))
done

KSH while loop Example

#!/bin/ksh
c=1
while [[ $c -le 5 ]]; do
 echo "Welcome $c times"
 (( c++ ))
done

CSH while loop Example

#!/bin/csh
c=1
while ( $c <= 5 )
 echo "Welcome $c times"
 @ c = $c + 1
end

Another example:

#!/bin/csh
set yname="foo"
while ( $yname != "" )
 echo -n "Enter your name : "
 set yname = $<
 if ( $yname != "" ) then
  echo "Hi, $yname"
 endif
end