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perlfunc:grep

by gods
on Aug 24, 1999 at 22:42 UTC ( #267=perlfunc: print w/replies, xml ) Need Help??

grep

See the current Perl documentation for grep.

Here is our local, out-dated (pre-5.6) version:


grep - locate elements in a list test true against a given criterion



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 a 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, because $_ is a reference into the list value, it can be used to modify the elements of the array. While this is useful and supported, it can cause bizarre results if the LIST is not a named array. Similarly, grep returns aliases into the original list, much like the way that 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.

See also map for an array composed of the results of the BLOCK or EXPR.


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[Corion]: Cosmic37: Basically, you read one file into a hash, keyed by your key, and then match the lines from the second file to that hash
[Cosmic37]: note that the two files only have datetimes which may match whereas other data per line is different format in file1 and file2 - is that really intersection?
[jedikaiti]: Hi Monks
[Corion]: Cosmic37: Well, if you want to use only parts of a line for the key, see split or whatever other mechanism to extract the key from the line
[Corion]: Hi jedikaiti!
[Cosmic37]: is there a webpage for full CB for this chat rather than side panel chat?
[Cosmic37]: thank you for advice
[Cosmic37]: peach greets jedi
[Cosmic37]: ok this one works better fullpage chat
[Cosmic37]: test

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