Perl: Run perl script in the current process - Shell Programming and Scripting

vino · #1 (**permalink**) 12-07-2005

I have a question regarding running perl in the current process.

I shall demonstrate with an example.

Look at this.

Code:

sh-2.05b$ pwd
/tmp
sh-2.05b$ cat test.sh
#! /bin/sh
cd /etc
sh-2.05b$ ./test.sh 
sh-2.05b$ pwd
/tmp
sh-2.05b$ . ./test.sh 
sh-2.05b$ pwd
/etc
sh-2.05b$

So invoking ./test.sh spawns a sub-shell and runs the script. Whereas . ./test.sh will run the script in the current shell.

Now, how can I simulate the latter behavior with a perl script. I tried the following but it did not help.

Code:

sh-2.05b$ pwd
/tmp
sh-2.05b$ cat test.pl
#! /usr/bin/perl
chdir("/etc");
sh-2.05b$ ./test.pl 
sh-2.05b$ pwd
/tmp
sh-2.05b$ . ./test.pl 
sh: ./test.pl: line 2: syntax error near unexpected token `"/tmp"'
sh: ./test.pl: line 2: `chdir("/tmp");'
sh-2.05b$

Is there any other way of running the script to make sure that the changes made by the script will affect the current process ?

Thanks,
Vino

jim mcnamara · #2 (**permalink**) 12-07-2005

AFAIK perl always creates a child.

Is there a reason you can't read the other script and do what it does in the context of the current process? ie., find the chdir and then do what it does in your perl script?

vino · #3 (**permalink**) 12-07-2005

Quote:

Originally Posted by jim mcnamara

Is there a reason you can't read the other script and do what it does in the context of the current process?

Yes, it can be done that way. That would work.

I am curious to know if it can be done this way.

Thanks,
vino

grasper · #4 (**permalink**) 12-07-2005

Just a guess, but I think the . command is instructing the current shell to interpret the script - which it can't because it has perl commands/functions in it.

cbkihong · #5 (**permalink**) 12-07-2005

The "exec" builtin in bash (sh on Linux seems to be too) will run the perl process without creating a new process by replacing the original shell process, just like the C exec* family of functions.

So you ought to be able to run a script by "./script.sh" to create a new process and then "exec perl script.pl" to continue execution without introducing a new process, but the original shell script will terminate (control will not return to the shell script).

zazzybob · #6 (**permalink**) 12-07-2005

Quote:

Originally Posted by cbkihong

The "exec" builtin in bash (sh on Linux seems to be too).....

On most (recent) Linux distros sh is soft/hard linked to bash...

Code:

# ls -l /bin/sh /bin/bash
-rwxr-xr-x  1 root root 616312 Dec  7  2004 /bin/bash
lrwxrwxrwx  1 root root      4 May 18  2005 /bin/sh -> bash

vino · #7 (**permalink**) 12-07-2005

Quote:

Originally Posted by cbkihong

The "exec" builtin in bash (sh on Linux seems to be too) will run the perl process without creating a new process by replacing the original shell process, just like the C exec* family of functions.

So you ought to be able to run a script by "./script.sh" to create a new process and then "exec perl script.pl" to continue execution without introducing a new process, but the original shell script will terminate (control will not return to the shell script).

Hmm...okie. So I used exec. This is what I got.

Code:

sh-2.05b$ pwd
/tmp
sh-2.05b$ cat test.sh
#! /bin/sh
exec perl /tmp/test.pl
sh-2.05b$ cat test.pl
chdir("/etc");
sh-2.05b$ ./test.sh
sh-2.05b$ pwd
/tmp
sh-2.05b$

I did a . ./test.sh and my xterm window just disappeared.

I changed test.pl to contain

Code:

#! usr/bin/perl
chdir("/etc");

and test.sh to

Code:

#! /bin/sh
exec /tmp/test.pl

The pwd still shows /tmp.

vino

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