Any errors in /var/cron/log or wherever you system keeps them? If you can't view that log, add 2>&1 (or whatever is appropriate on your system) to redirect STDERR to your own log file.

Your cron entry starts with "perl". Why, when you have #!/usr/bin/perl in your script?

I'd also add #!/path/to/expect -f to the .tcl, to simplify your $cmd.

And excessive pipe alert in your grep...

[root@perflnx14 SCRIPTS]# crontab -l
* * * * * /root/nfs_share/SCRIPTS/cron_ncp.pl >>/root/nfs_share/SCRIPT
+S/temp.txt 

---------------- cron_tab.pl script: 
#!/usr/bin/perl
use warnings;
use strict;
#my $cmd='nohup expect -f /root/nfs_share/SCRIPTS/ncp_run.tcl &';
my $cmd='nohup /root/nfs_share/SCRIPTS/ncp_run.tcl &';

#my $tmp= `ps -ef | grep -v grep | grep ncp_run.tcl | wc -l`;
my $tmp= `ps -ef | grep -c [n]cp_run.tcl`;

if($tmp == 1) {
print"already running\n";
} else {
print"not running\n";
system $cmd;
}

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