One way would be this: 
next if $field =~ /^(first|second|third)$/;

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The '^' matches the beginning of a string, and the '$' matches the end, emulating an 'eq' function for whatever's in between them. The '|'s are roughly equivalent to an 'or' statement: this will match 'first' or 'second' or 'third'.

Update: added explanation, and parens, thanks to Enlil.
--
Love justice; desire mercy.

In reply to Re: Fine tuning my condition statement by strider corinth
in thread Fine tuning my condition statement by Anonymous Monk

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