Not just eq/ne... but any expression that returns a true or false value — which implies: any expression in scalar context. (undef, "" and 0 are false, anything else is true.)

The generic variable $_ holds the value of the current item from the list. Actually, it's even stronger than that: $_ is an alias to the current item, which means: same value (by reference; you could say: same variable); different name. If you modify $_ in that expression, the original value will have changed. Example: 

@original= (0 .. 5);
@true = grep $_*=2, @original;
local $" = ", ";  # for nicely formatted output
print "original: @original\n";
print "output: @true\n";

[download]
Result: 
original: 0, 2, 4, 6, 8, 10
output: 2, 4, 6, 8, 10

[download]

Each item in the original array has been doubled. Of those, only the nonzero (true) values have been come through the grep filter.

In reply to Re^3: Using a Regexp to match a string exactly by bart
in thread Using a Regexp to match a string exactly by brainbuz

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