check out the docs for system. use the multiple argument form, and check the return code. also, use taint mode to check the arguments for nasty surprises. the following code is untested...

Update: note this code applies to any system calls, not just 'mv'. there are better tools for moving files, as mentioned by other monks.

#!/usr/bin/perl -wT
use strict;

## check your arguments
@_ == 2 or die "Usage: $0 from to\n";

## specify your command
my $cmd = '/usr/bin/mv';

## untaint your input
my( $from ) = ( $ARGV[0] =~ s/(\w|[/\\])+/$1/ );
my( $to ) = ( $ARGV[1] =~ s/(\w|[/\\])+/$1/ );

## make sure the input is good
( defined $from and defined $to ) or die "ERROR: $0 - bad input\n";

## run the command without using the shell
## check return code for errors
system( $cmd, $from, $to ) or die "ERROR: $0 - can't $cmd! $!";
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Update: escaped backslash in regex

~Particle *accelerates*