Shell Programming and Scripting

#!/bin/bash
BASH='/bin/bash'
KSH='/bin/ksh'
if [$SHELL == "$BASH"]
then
echo "it's Bash"
else
echo "it's not Bash"
fi

$ bash -x a.sh
+ BASH=/bin/bash
+ KSH=/bin/ksh
+ '[/bin/bash' == '/bin/bash]'
a.sh: line 4: [/bin/bash: No such file or directory
+ echo 'it'\''s not Bash'
it's not Bash

echo $0

 cat vartest.sh
#!/bin/sh

usage()
{
   echo "Usage:"
   echo "      $0 \$0"
}

if [ $# -lt 1 ] ; then
   echo "Don't forget to send the shell information"
   usage
   exit 1
fi

echo "the shell is $1"
exit 0

./vartest.sh
Don't forget to send the shell information
Usage:
      ./vartest.sh $0

./vartest.sh $0
the shell is -bash

#!/bin/bash

if [ "$SHELL"  == "/bin/bash" ]
then
    echo "blah"
else
    echo "aaa"
fi