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

hi, I was wondering and even took a fast look at perlopentut and perldoc -f open, but didnt found something to just grep over file inside perl script w/o first opening the file, grepping and then closing (which sometimes is boring)..
Example, currently I often use something in the lines of :
my $line = qx{grep "^ARGV[0]\|" filename.txt}

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So that I dont do : 
open FILE, .... or die "blah...:$!";
..grep it...
close FILE;

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do u get the idea..shortcuts :").. it there something in the core-packges that will work like this...
yep i know i can make it like sub(), but the idea was to just write and forget and not forking grep...

tia

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Re: quick "open->close" file
by davorg (Chancellor) on Aug 06, 2003 at 11:50 UTC

    If (as your example implies) the filename is passed as the first command line argument, then you can use the empty file input operator (<>) to read from it.

    my @found = grep { something } <>;

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    --
    <http://www.dave.org.uk>

    "The first rule of Perl club is you do not talk about Perl club."
    -- Chip Salzenberg

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      nope, the filename is not passed in @ARGV.. what comes in @ARGV is for what to search in files..
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        the filename is not passed in @ARGV

        Of course there's nothing to stop you putting it there :)

        my @args = @ARGV;
@ARGV = 'filename.txt';
my @found = grep { /^args[0]/ } <>;

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        --
        <http://www.dave.org.uk>

        "The first rule of Perl club is you do not talk about Perl club."
        -- Chip Salzenberg

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Re: quick "open->close" file
by broquaint (Abbot) on Aug 06, 2003 at 12:25 UTC
    Or if you want to perform this on an arbitrary file 
    use IO::File;

my $line = -f $file and grep { ... } IO::File->new($file)->get_lines;

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    So if $file exists, create a temporary IO::File object and read its contents. Not as robust as the <> solution, but it does perform an open/read/close.
    HTH

    _________
    broquaint

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      Minor correction: Replace "get_lines" with "getlines". 
      use IO::File;
my $line = -f $file and grep { ... } IO::File->new($file)->getlines;
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Re: quick "open->close" file
by Aristotle (Chancellor) on Aug 06, 2003 at 15:15 UTC
    Lazy solution causing the whole file to be slurped up front: 
    my @match = do {
    open my $fh, '<', $file or die "$!";
    grep /^$ARGV[0]\|/, <$fh>;
};

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    If your file is large, it takes more effort. 
    my @match;
{
    open my $fh, '<', $file or die "$!";
    local $_;
    my $rx = qr/^$ARGV[0]\|/
    m/$rx/ && push @match, $_ while <$fh>;
}

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    If I need the latter more than once, I'd probably factor it out: 
    sub grep_file {
    my ($rx, $file) = @_;
    my @match;
    local $_;
    open my $fh, '<', $file or die "$!";
    my $rx = qr/^$rx\|/
    m/$rx/ && push @match, $_ while <$fh>;
    @match;
};

my @match = grep_file($ARGV[0], $file);

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    Makeshifts last the longest.

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