Read perldoc -f eval. But here's a sample:

#!/usr/bin/perl
use strict;

eval { require foo::bar }; 
# errors stored into $@
warn $@ if $@;

# also, you can set a flag to see if the module
# was available:
my $use_foo_bar = 1 unless $@;

print "I'm still going...\n";

if ($use_foo_bar)
{
    foo::bar::function();
}
else
{
    print "No foo for you\n";
}
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