Seeking multiple defined files

DaWolf has asked for the wisdom of the Perl Monks concerning the following question:

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Re: Seeking multiple defined files by Fastolfe (Vicar) on Nov 21, 2000 at 21:07 UTC
You're using (parenthesis) when you should be using {curly-braces}. The first argument to grep is a `{ BLOCK }` that describes how you want to search the items in the following list. `@existing_files = grep { -e $_ } @untested_files;` [download] This will return true for any item that can be said to "exist" in the file system. You may want to use `-f` to test if it's a file (versus, say, `-d` to see if it's a directory), etc. See _X for additional tests you can perform. Note also that `$_` is implied, so you can leave that out: `{ -e }` `# alternate syntax @exiting = grep(-e, @untested);` [download] See the documentation for grep, which is what I would have done in the first place.	[reply] [d/l] [select]
Re: Seeking multiple defined files by mikfire (Deacon) on Nov 21, 2000 at 21:13 UTC
merlyns's comment is on the button. Becuase I am in hard core work avoidance mode, though, I will offer some suggestions Most of these snippets will assume the list of filenames is in ( imagine this ) @filenames. I will state other assumptions later If you don't care to preserve the filenames, this one is kinda neat. It is compact and has the convenient side effect of giving you the name of the file that first matched. `shift @filenames while ( @filenames && ! -e $filenames[0] ); die "No names matched" unless ( @filenames );` [download] If you must preserve the data, you will likely want a foreach loop. This loop will also preserve any match. It is also a bit more verbose than the previous example. `my $found = ''; foreach ( @filenames ) { next unless -e $_; $found = $_; last; }` [download] These will give you better average case performance than either of the two methods you mentioned in your question. The grep-map combo is really nasty - it will walk through the entire list twice even if the first file in the list exists. Mik mikfire	[reply] [d/l] [select]
Re: Seeking multiple defined files by chromatic (Archbishop) on Nov 21, 2000 at 21:01 UTC
The first of the two chatterbox solutions (mine, actually :) works fine on my machine. What is the syntax error you are receiving? (add 'use diagnostics;' to the start of your program and see if that helps your debugging.)	[reply]
Re: Re: Seeking multiple defined files by DaWolf (Curate) on Nov 21, 2000 at 21:14 UTC
Hi Chromatic. I've tried the command you've putted: `grep (-e $_) @files;` I receive these error messages: Array found where operator expected at foo.cgi line 187 at end of line. (Missing operator before ?) Not enough arguments for grep at foo.cgi line 187 near "$_)" Syntax error at foo.cgi line 187, near ") @files" Er Galvão Abbott a.k.a. Lobo, DaWolf Webdeveloper	[reply] [d/l]
Re: Seeking multiple defined files by merlyn (Sage) on Nov 21, 2000 at 20:55 UTC
This would be a FAQ. "How can I tell whether a list or array contains a certain element?", in perlman:perlfaq4. -- Randal L. Schwartz, Perl hacker	[reply]