Grep to find item in Perl array

Question

Every time I input something the code always tells me that it exists. But I know some of the inputs do not exist. What is wrong?

#!/usr/bin/perl

@array = <>;
print "Enter the word you what to match\n";
chomp($match = <STDIN>);

if (grep($match, @array)) {
    print "found it\n";
}

Answer 1

The first arg that you give to grep needs to evaluate as true or false to indicate whether there was a match. So it should be:

# note that grep returns a list, so $matched needs to be in brackets to get the 
# actual value, otherwise $matched will just contain the number of matches
if (my ($matched) = grep $_ eq $match, @array) {
    print "found it: $matched\n";
}

If you need to match on a lot of different values, it might also be worth for you to consider putting the array data into a hash, since hashes allow you to do this efficiently without having to iterate through the list.

# convert array to a hash with the array elements as the hash keys and the values are simply 1
my %hash = map {$_ => 1} @array;

# check if the hash contains $match
if (defined $hash{$match}) {
    print "found it\n";
}

Answer 2

You seem to be using grep() like the Unix grep utility, which is wrong.

Perl's grep() in scalar context evaluates the expression for each element of a list and returns the number of times the expression was true. So when $match contains any "true" value, grep($match, @array) in scalar context will always return the number of elements in @array.

Instead, try using the pattern matching operator:

if (grep /$match/, @array) {
    print "found it\n";
}