Shell Programming and Scripting

#!/bin/ksh

if [ -z "$BASH_VERSION" ]
then
    echo hi

fi

-z string = True if the length of the string is 0.

echo ${#BASH_VERSION}

#!/bin/bash
echo "bash version = $BASH_VERSION, length = ${BASH_VERSION}"

bash-4.2$ echo $BASH_VERSION
4.2.50(1)-release
bash-4.2$ ksh
$ echo $BASH_VERSION

$

bash-4.2$ echo ${#BASH_VERSION}
17
bash-4.2$ ksh
$ echo ${#BASH_VERSION}
0
$

$ cat t.shl
#!/bin/bash

if [ -z "$BASH_VERSION" ]
then
    echo hi
else
    echo "characters found"
fi

Owner@Owner-PC ~
$ ./t.shl
characters found

$ cat t.shl
#!/bin/dash

if [ -z "$BASH_VERSION" ]
then
    echo hi
else
    echo "characters found"
fi

Owner@Owner-PC ~
$ ./t.shl
hi

. scriptname