System, backticks, open, and exec

Perl offers many ways to call external programs

# launch an editor for the user
my $EDITOR = $ENV{VISUAL} || $ENV{EDITOR} || 'vi';
system( "vi $tmpfile" );

# Find the user accessing /tmp/somefile
my $abuser = `/bin/fuser /tmp/somefile`;

# ROT13 decode the userinput
open ROT13, "|rot13";
print ROT13 $userinput;
close ROT13;

# stop our perl script entirely, run something else
exec "/usr/bin/nmap -A www.microsoft.com"