- 论坛徽章:
- 0
|
grep BLOCK LIST
grep EXPR,LIST
This is similar in spirit to, but not the same as, grep(1) and
its relatives. In particular, it is not limited to using regular
expressions.
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.
@foo = grep(!/^#/, @bar); # weed out comments
or equivalently,
@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. |
|