A perl issue when execute system call

[jeanwelly]

Hi,
I met with a hang issue when using perl in some Unix server, don't
why? Could you help?

print "start...\n";
my $result = `which command`;
print "Stop...\n"; # can not call to here.
chomp($result);

It looks really strange to me. Thanks!

 

[Mirco Wahab]

I met with a hang issue when using perl in some
Unix server, don't why? Could you help?

print "start...\n";
my $result = `which command`;
print "Stop...\n"; # can not call to here.
chomp($result);

What is "command"?

What happens if you put the "command"
into a shell?

$~jeanwelly> command [enter]


Regards

M.

 

[Mirco Wahab]

Not "what" - "which". It's a *nix command that crawls your PATH and reports
where it finds the first occurrence of "command".

Of course, you are correct. I didn't
really touch the problem here, sorry.

Regards & thanks for corrections

M.

 

[jeanwelly]

Hi Everyone,
Sorry for not presented my problem clearly, here is clarification.
`which whois`; # it will hang.

It is executed in SUN UNIX OS, and some seems fine, some no; if key
the command in shell directly, it tell me "shell built in command" in
the issued SUN server; while in another SUN server that without this
hang issue, the shell tells me the correct directory.

For how long that I waited for the response, the answer is whole
night

 

[jeanwelly]

One more info: in perl script, `which who`; will not hang, but `which
whois`;.

Thanks!

 

[jeanwelly]

Hi Glenn,
Actually I was using `which upd` to got the full datapath of clearcase
bin/upd command, when I debug, I found similar hang issue of `which
whois`, due to different server setup, I can't rely on the PATH to
tell where is the bin/upd.

The interesting thing is in SUN server1 I have the issue, but no in
SUN server2, and the two with same kernel version and perl verison.

 

[jeanwelly]

Hi Glenn,
Actually I was using `which upd` to got the full datapath of clearcase
bin/upd command, when I debug, I found similar hang issue of `which
whois`, due to different server setup, I can't rely on the PATH to
tell where is the bin/upd.

The interesting thing is in SUN server1 I have the issue, but no in
SUN server2, and the two with same kernel version and perl verison.

At 2007-07-20 07:05AM, "jeanwelly" wrote:

What shell do you use that has whois as a builtin command?

Doesn't 'which' read your .cshrc to learn about aliases? Do you have
anything in .cshrc that might be interfering?

Anyway, you shouldn't be relying on the PATH in a Perl program -- it's a
security issue. Either specify the full path /usr/bin/whois where you
need it, or set $ENV{PATH} yourself to something like '/usr/bin:/bin'.

Anyone has any suggestions to check? I'm still in the trouble.
One of my workmate can use his account in the server (I encountered
with hang issue) with NO the hang issue. I sourced his .cshrc, but
still does not work.

 

[Joseph.Trapasso]

Anyone has any suggestions to check? I'm still in the trouble.
One of my workmate can use his account in the server (I encountered
with hang issue) with NO the hang issue. I sourced his .cshrc, but
still does not work.

Rewrite your own version of which within perl:
#!/usr/bin/env perl

use strict;
use warnings FATAL => 'all';

unless(@ARGV){
print "Too few arguments\n";
exit;
}

foreach my $file(@ARGV){
my $path = (grep {-e "$_/$file"} split(/:+/, $ENV{PATH}))[0];
if($path){
print "$path/$file\n";
}else{
print "$file: Command not found.\n";
}
}

Running it gives me:
l-xterm-7:~/sandbox/scratch> ./perlWhich.pl perl doggy fish gdb whois
/home/utils/perl-5.8.8/bin//perl
doggy: Command not found.
fish: Command not found.
/usr/bin/gdb
/usr/bin/whois
l-xterm-7:~/sandbox/scratch>