test script to identify SHELL

Shell Programming and Scripting
1

I am new to BASH and writing a small script to identify the SHELL .

#!/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

where am I missing . PLease advice .

Thanks

2

have you tried:

echo $0

the $SHELL variable refers to the user's default shell (in /etc/passwd) - it may not reflect the shell that the user is currently running.

3

Read the error message. What command is not found? Is that the command you are trying to execute?

You are missing spaces before and after brackets:

if [ "$SHELL" = "$BASH" ]

Note that $SHELL doesn't necessarily contain the shell you are currently running; it contains your default shell.

4

You need a blank between both variables and the square brackets, otherwise neither shell can parse it correctly. And it would be advisable to put the $SHELL variable in quotes too.

5

Thankyou .

if you put "echo $0" inside the script , it will give the script name .

Thanks

6

Having said "echo $0", this won't work inside the shell script.
Calling $0 inside a sh/bash/ksh script will recall the name of the script.
You can pass this TO your script at the command line.
For example:

 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
7

Thankyou .

My problem is it's not seperate script . I have to include it in another script .

can you think of any other logic to identify the shell inside another script ..

#!/bin/bash

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

Thanks

8

Why do you need to know what shell it is?

It is better to test for the features you want.

You can check for variables $BASH_VERSION and $KSH_VERSION (the latter only in pdksh).

9 
#!/bin/sh

pid="$$"
echo "myShell->[`ps -o 'pid,comm' -p "${pid}" | nawk 'FNR==2{print $2}'`]"

YMMV - not generic

10

Using any standard version of ps (and no other external command) in any Bourne-type shell:

ps -o comm -p "$$" | { read; read comm; echo "$comm"; }

However, that doesn't necessarily tell you anything about the shell, particularly if it's sh.

11

I don't think that $SHELL is the right variable to test. Anyway, on a point of syntax the "==" is not valid in "test" when it is not bash.
cfajohnson approach to find a suitable variable which is only set by that shell is better. Use "if [ -z "${SUITABLE_VARIABLE}" ] .