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Re^2: eof not recognised when applying diamond operator to invocation arguments?

by pat_mc (Pilgrim)
on Jan 12, 2011 at 16:53 UTC ( #881946=note: print w/ replies, xml ) Need Help??


in reply to Re: eof not recognised when applying diamond operator to invocation arguments?
in thread eof not recognised when applying diamond operator to invocation arguments?

Hm ... thanks, Illuminatus ... I looked at that link ... not sure it provided me with the answer (or at least - if it did, I did not get it). Could you please be a little more verbose? Your wisdom will be much appreciated!

Pat


Comment on Re^2: eof not recognised when applying diamond operator to invocation arguments?
Re^3: eof not recognised when applying diamond operator to invocation arguments?
by Illuminatus (Curate) on Jan 12, 2011 at 17:50 UTC
    When you do not explicitly open the files by name, but simply start using <>, you are reading a catenation of all of the files on the command line. Therefore, the first time through the loop, you read all of the files. As the link implied, $ARGV refers to whatever file <> is currently referencing (the last one). If you want it to work as you intend, you could do something like:
    foreach my $file (@ARGV) { open (FILE, $file) || die "could not open $file"; while (<FILE>) { print $_; } close FILE; print "whatever you wanted to use as a separator $file\n"; }

    fnord

      Style tips.
      • Using 2 argument open is potentially buggy if the file name can contain unusual characters like ">" or "|". It is therefore a good habit to use 3 argument open instead. Note that this error is implicit in <>, which is a reason not to use it. See magic-diamond <> behavior -- WHAT?! for an explanation.
      • As perlstyle says, you should always include $! in your error messages. Always, always, always.
      • I've personally encountered enough cases where a file can't be opened because the filename includes accidental whitespace that I like to always quote it in the error message.
      • There is no need to explicitly close the filehandle since Perl does it for you. (And does it quite promptly if you're using lexically scoped filehandles. Which you are not.) Unless, of course, you are concerned that the close may fail and are error checking it. If you're serious about error checking, I would recommend using autodie.
      With those changes your snippet becomes:
      foreach my $file (@ARGV) { open (FILE, "<", $file) || die "could not open '$file': $!"; while (<FILE>) { print $_; } print "whatever you wanted to use as a separator $file\n"; }
      Getting more contentious, if you spell "foreach" as "for", add the normal indentation and brace style, lexical filehandles, and convert the while into an inline form, you get the more idiomatic:
      for my $file (@ARGV) { open (my $fh, "<", $file) || die "could not open '$file': $!"; print while <$fh>; print "whatever you wanted to use as a separator $file\n"; }

      Edit: Argel is right. The for/foreach distinction belongs in the stylistic nitpicks, not in the more substantive section.

        Don't you think the "foreach" comment is nitpicking a bit? It's an alias to "for" and when performing the loop the the Perlish way the phrase "for each element" makes more sense than "for element". Meanwhile, when using it the repressed memory inducing, nightmarish C-style way, the phrase "for this series of numbers" is a better fit. In my experience, "foreach" is easier for people new to programming to grasp and it makes it easier to wean C-junkies off of the C-styled for loops.

        Elda Taluta; Sarks Sark; Ark Arks

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