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comamnds running interactively, failed in script wrigint

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Top Forums Shell Programming and Scripting comamnds running interactively, failed in script wrigint
# 1  
Old 09-25-2012
comamnds running interactively, failed in script wrigint
Hi all,
I am trying to run these commands in shell script, but there seem to be some mistake. Somehow it is not accepting the last important comamnd "eval `scram runtime -sh`". However, when I try them interactively, it works all fine.
Code:
[pooja04@cmslpc07 v6]$ SOURCEPATH=/uscms_data/d3/pooja04/CMSSW_5_3_3_patch2/src/ElectroWeakAnalysis/MultiBosons/test/
[pooja04@cmslpc07 v6]$ cd $SOURCEPATH
[pooja04@cmslpc07 test]$  eval `scram runtime -sh`

SCRIPT
====
Code:
SOURCEPATH=/uscms_data/d3/pooja04/CMSSW_5_3_3_patch2/src/ElectroWeakAnalysis/MultiBosons/test/

SetEnv () {
    SCRIPT=`readlink -f $0`

    SCRIPTPATH=`dirname $SCRIPT`
    cd $SOURCEPATH
    echo  $SOURCEPATH
    eval `scram runtime -sh`
    cd $SCRIPTPATH
}

any piece of hint is appreciable.

Thanks
# 2  
Old 09-25-2012
You cannot depend on $0. It may be an absolute path, relative path, or no path depending on how the program is run.
# 3  
Old 09-25-2012
hi corona,
I did not understand. I have tested that piece of code. It just cd in the current working directory.
# 4  
Old 09-25-2012
Quote:
Originally Posted by nrjrasaxena
hi corona,
I did not understand. I have tested that piece of code. It just cd in the current working directory.
You've tested it in your home dir, by running it in a manner where $0 can be depended on.

Except, you can't depend on $0. When something that's not you runs it, especially automatic things like cron and so forth, you have no idea what your current dir, and the contents of $0, are going to be. It might start in / with a useless $0 like -bash or something. Or it might give an absolute path you weren't expecting. etc. I keep telling people not to do this but until it breaks down like this, they never understand why.

Try typing echo $0 into your shell for example. I get -bash. That's not any sort of directory.
# 5  
Old 09-25-2012
Quote:
Originally Posted by Corona688
You've tested it in your home dir, by running it in a manner where $0 can be depended on.

Except, you can't depend on $0. When something that's not you runs it, especially automatic things like cron and so forth, you have no idea what your current dir, and the contents of $0, are going to be. It might start in / with a useless $0 like -bash or something. Or it might give an absolute path you weren't expecting. etc. I keep telling people not to do this but until it breaks down like this, they never understand why.

Try typing echo $0 into your shell for example. I get -bash. That's not any sort of directory.

I just tested that piece of code as script like this [1] and the output is [2] just as I want it to be.
It take me back to my working directory.

[1]
Code:
SetEnv () {
    SCRIPT=`readlink -f $0`
    echo $SCRIPT
    SCRIPTPATH=`dirname $SCRIPT`
    cd $SOURCEPATH
    echo  $SOURCEPATH
    eval `scram runtime -sh`
    cd $SCRIPTPATH
    echo $SCRIPTPATH
}

[2]
Code:
[pooja04@cmslpc17 v6]$ ./script.sh  setenv
Tue Sep 25 15:33:30 CDT 2012
/uscms/home/pooja04/script/AnalysisCode/Code42012/v6/Script4JobSubmit.sh
/uscms_data/d3/pooja04/CMSSW_5_3_3_patch2/src/ElectroWeakAnalysis/MultiBosons/test/
/uscms/home/pooja04/script/AnalysisCode/Code42012/v6
[pooja04@cmslpc17 v6]$

# 6  
Old 09-25-2012
$0 does not mean "path to my program". That's what it traditionally is, and it's what you get whenever a shell runs a program, but when something that's not a shell runs your program, that's not guaranteed by any means. cron will give weird values for $0. CGI gives weird values for $0. And so forth.

So yes... It does when you run it, from a terminal, giving it an absolute path. When things other than you run it, from non-terminals, in ways and from places you never did, you might get something else.

These two C programs show how it works:

Code:
$ cat printzero.c

#include <stdio.h>

int main(int argc, char *argv[])
{
        printf("$0 is %s\n", argv[0]);
}

$ cat zero.c

#include <unistd.h>
#include <stdio.h>

int main(int argc, char *argv[])
{
        if(argc < 2)
        {
                fprintf(stderr, "usage:  ./zero program zeroth-argument\n");
                return(1);
        }

        // First argument is the program name and path.  Second is $0.
        // Note that NOTHING forces them to be the same.
        execl(argv[1], argv[2], NULL);
        return(1);
}

$ gcc zero.c -o zero
$ gcc printzero.c -o printzero
$ ./printzero

$0 is ./printzero

$ ./zero ./printzero slartibartfast

$0 is slartibartfast

$

So, when you run ./printzero by itself, the shell runs it, and $0 is what you expect.

When the zero program runs printzero, it can give whatever weird and wild value it wants to $0, and does.

Some shells will make a halfhearted attempt to correct the value of $0 into something 'useful', but they're not psychic. They can't recover paths they were never given in the first place.

So $0 is only what the program calling it says it is. It's not necessarily the information you want. Do not depend on it if you want your scripts to be run by cron and the like.
Last edited by Corona688; 09-25-2012 at 06:14 PM..
# 7  
Old 09-25-2012
What's the output of scram runtime -sh ? Is it different in the script or from the command line?
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