Bash question....

jonnybinthemix · 05-20-2014, 04:11 AM

Hey Guys,

I've been studying Linux for several months now and am trying to get my head around bash scripting.

I'm playing around with a simple script that will echo one thing if it's run by a particular user and will echo something else if run by another user again..

I've got this so far:

Code:

!/bin/bash

if [[ $EUID -eq 0 ]]; then
   echo "root"

if [[ $EUID -eq 500 ]]; then
   echo "jon"
else
exit 1
fi
fi

The UID for jon is 500 and of course root is 0... in theory I'm sure this should work.. but maybe my syntax is wrong?

Any help would be appreciated.

Thanks
Jon

Shadow_7 · 05-20-2014, 04:49 AM

I'm more likely to enclose the values in quotes and use the = sign. Although there's probably more modern syntax options these days.

if [ "$EUID" = "0" ]; then
...
fi

Although your script seems a bit unneccessary.

$ whoami

$ groups | awk '{ print $1; }'

would both return basically the same end result. Without having to hard code an ID value or introduce conditionals.

jonnybinthemix · 05-20-2014, 04:59 AM

Hey,

I actually just figured it out.. I ended up with:

Code:

!/bin/bash

if [[ $EUID -eq 500 ]]; then
   echo "Jon"

else

if [[ $EUID -eq 0 ]]; then
   echo "root"

exit 1
fi
fi

However I'm open to a way of carrying it out more efficiently.. I like the idea of the whoami variable but I was thinking that the UID would be more solid.. but I guess it doesn't really matter in that instance. Less code is better, I'll have a play around with it more.

I guess my next step is to add another section where it will return a usage message if run by a different user.

chrism01 · 05-20-2014, 06:06 AM

I don't see why the exit cmd is called if root user? Also, 1st line is wrong...
How about

Code:

#!/bin/bash
if [[ $EUID -eq 500 ]]
then
   echo "Jon"
elif [[ $EUID -eq 0 ]]
then
   echo "root"
else
    echo "neither ..."
fi

jonnybinthemix · 05-20-2014, 07:31 AM

Hey,

Thanks for your reply.

The first line 'shebang' in my script does have the hash, it just for some reason didnt paste into here

I put the Exit in as I want the script to end if none of the statements are true.. but I guess it will end anyway based on what you said?

Tried elif before, but couldn't get it working. Must have had some incorrect syntax.

Will have another play around.

Thanks
Jon

grail · 05-20-2014, 09:32 AM

My general suggestion when performing arithmetic tests is to use the brackets designed for that:

Code:

if (( EUID == 0 ))
then
...

The nice thing about them is you can use all the traditional mathematic symbols, such >, <, >=, etc

unSpawn · 05-20-2014, 11:32 AM

Quote:

Originally Posted by jonnybinthemix

I've been studying Linux for several months now and am trying to get my head around bash scripting.