Difference between source and dot command in Linux

itismohit · 06-14-2010, 01:26 AM

Hi,

I have written a set of aliases in a file.
When i tried to dot it( "Prompt> . filename" ). It said
" .: Permission denied. "
But, when I sourced it ("Prompt> source filename"). It worked perfectly.

Linux manual has one entry for both the commands. Then what am I missing ?

RockDoctor · 06-14-2010, 07:09 AM

Quote:

Originally Posted by itismohit

Hi,

I have written a set of aliases in a file.
When i tried to dot it( "Prompt> . filename" ). It said
" .: Permission denied. "
But, when I sourced it ("Prompt> source filename"). It worked perfectly.

Linux manual has one entry for both the commands. Then what am I missing ?

Check the file's permissions with

Code:

ls -l <filename>

It's probably something like rw-rw-r--; in other words, it's not marked as executable. You'll need to use the chmod command to change the permissions; something like

Code:

chmod 775 <filename>

colucix · 06-14-2010, 07:26 AM

@RockDoctor: actually the files don't need executable permissions, just for the fact they are sourced and not executed.

@itismohit: in BASH the . and the source built-ins are synonyms. Historically the . is the name of the source command for the Bourne Shell, whereas source is the name for C-shells.

I suspect your user's shell is not BASH, since it should manage the two versions properly. Unlike C-shells (e.g. /bin/tcsh) that recognize only source and not dot.

itismohit · 06-15-2010, 02:39 AM

@colucix

Thanks man. Yes, my shell is tsch.
I completely agree with you, but that entails another question.

I am wondering why am I getting an error of ".: permission denied" and not ".:command not found".

"prompt> which ." on tsch gave me ".:command not found", but typing
"prompt> . " on tsch is giving ".: permission denied."

what is dot being mapped to by tsch ?

colucix · 06-15-2010, 02:54 AM

The C-shell interprets the "command" . as the "current working directory". It tries to execute a current working directory somewhere in the PATH. You can easily verify it using this dummy script:

Code:

#/bin/tcsh -x
.

On my system it results in:

Code:

$ chmod 744 test.csh
$ ./test.csh
.
/usr/bin/.: Permission denied.

The -x option echoes the commands before the execution (first line echoes the dot). As you can see, here the dot (as command) is mapped to /usr/bin/. hence the permission denied error (since a directory has the executable bit, but you don't have permission to actuall "execute" it).

itismohit · 06-16-2010, 03:42 AM

That pretty much wraps it all.
Thanks again.