Perl 5 version 28.3 documentation


  • grep BLOCK LIST

  • grep EXPR,LIST


    Evaluates the BLOCK or EXPR for each element of LIST (locally setting $_ to each element) and returns the list value consisting of those elements for which the expression evaluated to true. In scalar context, returns the number of times the expression was true.

    1. my @foo = grep(!/^#/, @bar); # weed out comments

    or equivalently,

    1. my @foo = grep {!/^#/} @bar; # weed out comments

    Note that $_ is an alias to the list value, so it can be used to modify the elements of the LIST. While this is useful and supported, it can cause bizarre results if the elements of LIST are not variables. Similarly, grep returns aliases into the original list, much as a for loop's index variable aliases the list elements. That is, modifying an element of a list returned by grep (for example, in a foreach, map or another grep) actually modifies the element in the original list. This is usually something to be avoided when writing clear code.

    See also map for a list composed of the results of the BLOCK or EXPR.