commify_series script in cookbook page 94



While reading perl cookbook, I came to page 94 and having a hard time understanding this particular phrase

my $sepchar = grep( /,/ => @_ ) ? ";" : ",";

I recognize the ternary operator and grep but I am not sure how they are forming the meaning together.

I thought grep needed lists to work on ? and grep(/,/ => @_), I am not sure where it's getting the list from

my @results = grep EXPR, @input_list;
my $count = grep EXPR, @input_list;

And I also don't understand what ";" is doing in the ternary operator??

I think I understand the rest of the program though..

Can someone help me out please?

thank you.

-------------------- Complete program --------------------------
#!/usr/bin/perl -w

use strict;

my @lists = (
[ 'just one thing' ],
[ qw(Mutt Jeff) ],
[ qw(peter Paul mary) ],
[ 'To our parents', 'Mother Theressa', 'God' ],
[ 'pastrami', 'ham and cheese', 'peanut butter and jelly', 'tuna' ],
[ 'recycle tired, old phrases', 'ponder big, happy thoughts' ],
[ 'recycle tired, old phrases',
'ponder big, happy thoughts',
'sleep and dream peacefully' ],
);

for my $aref ( @lists ) {
print "The list is: ". commify_series( @$aref ) . ".\n";
}

sub commify_series {
my $sepchar = grep( /,/ => @_ ) ? ";" : ",";
( @_ == 0 ) ? ''
: ( @_ == 1 ) ? $_[0]
: ( @_ == 2 ) ? join(" and ", @_ )
: join("$sepchar ", @_[0 .. ($#_-1) ], "and $_[-1]" );
}

.