[SOLVED] Use of cmd=`basename $0` in shell scripting

shivaa · 10-05-2012, 09:03 PM

Hello friends,
I have seen in many shell scripts, the variable used cmd=`basename $0`
What's use of this variable in a shell script? Is it necessory?
Though I've read one thread on the same, but that was not so informative.
So please give your expert opinions.
Thanks in advance!

unSpawn · 10-05-2012, 09:41 PM

Quote:

Originally Posted by meninvenus

What's use of this variable in a shell script?

That depends on the script ;-p You could use it for instance to find out what the script is called as. Like altering script execution by calling it via different named symbolic links.

Quote:

Originally Posted by meninvenus

Is it necessory?

If you need it, and there's no other or more efficient method, then it's necessary ;-p

Toggan · 10-05-2012, 10:26 PM

From what it looks like, basename is a way to get the name of a file without an extension and the $0 variable is the name of the script being run.

This would mean that if you're running a script called script.sh, when cmd is called, it will just be equal to script.

colucix · 10-06-2012, 03:29 AM

Quote:

Originally Posted by Toggan

From what it looks like, basename is a way to get the name of a file without an extension and the $0 variable is the name of the script being run.

This would mean that if you're running a script called script.sh, when cmd is called, it will just be equal to script.

Not really true. basename removes the leading path and leaves the filename intact. For example

Code:

/directory/somewhere/in/my/system/script.sh

becomes

Code:

script.sh

Regarding the suffix, it is an additional feature: if you specify a second argument to basename it will be treated as a suffix to remove, so that in the previous example the command

Code:

basename /directory/somewhere/in/my/system/script.sh .sh

leaves only script.

Toggan · 10-06-2012, 10:29 AM

Quote:

Originally Posted by colucix

Not really true. basename removes the leading path and leaves the filename intact. For example

Code:

/directory/somewhere/in/my/system/script.sh

becomes

Code:

script.sh

Regarding the suffix, it is an additional feature: if you specify a second argument to basename it will be treated as a suffix to remove, so that in the previous example the command

Code:

basename /directory/somewhere/in/my/system/script.sh .sh

leaves only script.

Thanks for clearing that up, that explains why most of where I've seen basename used is in init scripts. They don't have file extensions and it may be necessary to call back to what service is being started/stopped.

H_TeXMeX_H · 10-06-2012, 11:12 AM

Read 'man basename' for all of its features.

Do not use backticks use this instead:

Code:

cmd="$(basename $0)"

One use that I often use it for is to provide usage information, and you don't know if someone has retitled your script. You can also use it to remove a suffix, but that is not its main feature.

pan64 · 10-06-2012, 12:01 PM

pretty strange, noone mentioned, basename is an external utility, and this can be solved inside bash.

Code:

X=$0        # save $0 in a local variable
Y=${X##*/}  # remove dir part
Z=${Y%.*}   # remove extension - if you want to do so

http://splike.com/wiki/Bash_Scriptin...unctions.29.3F - there is a typo on that page, so probably this one is better: http://linuxgazette.net/18/bash.html

TobiSGD · 10-06-2012, 12:48 PM

As long as you use Bash you are right, no need for basename. But many scripts are written POSIX compliant, which doesn't nknow of that substitution features of Bash (and other shells). So if you aim at portability basename is the preferred solution.