Line number in a file

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

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Re: Line number in a file by pelagic (Priest) on Jul 06, 2004 at 08:36 UTC
Your code doesn't show how you process your file initially but maybe you don't know the special variable $. `while (<FILE>) { if (/what not/) { print "We found what not in line $.\n"; } }` [download] more info perlvar pelagic	[reply] [d/l]
Re: Line number in a file by davidj (Priest) on Jul 06, 2004 at 09:04 UTC
You might consider this a nitpick, but the replies by pelagic and busunsl need a clarification. To the best of my knowledge, the built-in Perl variable `$.` is technically the record number variable, not the line number variable, and a record is not always a line. It all depends upon the value of `$/`, the record separator variable. By default it is newline, but it can be changed. I mention this only because I once had a terrible time debugging a (poorly written) script which read from a file, used `$.`, and the script writer had changed the value of `$/`. It took me some time to figure that out. davidj	[reply] [d/l] [select]
Re^2: Line number in a file by pelagic (Priest) on Jul 06, 2004 at 09:39 UTC
> It all depends upon the value of $/, the record separator variable. Of course if you read a file in slurp mode you actually just read 1 record and the official name INPUT_LINE_NUMBER is somewhat misleading because lines become a logical measure. And if you set $/ to some weird separator the meaning of line is actually set to something completely different. pelagic	[reply]
Re^2: Line number in a file by Anonymous Monk on Jul 07, 2004 at 06:32 UTC
the script writer had changed the value of $/. I hope you ~~berated~~ gave him a "talking to" about not using local (appropriately).	[reply]
Re^3: Line number in a file by davidj (Priest) on Jul 07, 2004 at 16:51 UTC
Well, I was considering requesting that his Perl privileges be temporarily suspended, but then, how could he learn to write better code. So, instead, I smacked him on the head with the Camel book :) davidj	[reply]
Re: Line number in a file by busunsl (Vicar) on Jul 06, 2004 at 08:37 UTC
When you read the file line by line, $. will give you the current linenumber. If you just slurp it, you'll have to set up a counter.	[reply]
Re: Line number in a file by edan (Curate) on Jul 06, 2004 at 09:58 UTC
I think the others have answered your question about how to get the line number in the file-reading loop using `$.`. But your question also seems to be "How do I save off the value for later use?" Maybe I'm misunderstanding the question, or maybe my answer is blindingly obvious to you once you know about `$.`, but here is an example (using your own example code) of how you might save off that info for later use when you process the data you collected: `while (<MYFILE>) { $alldata .= $_ ; if(/(\S+)\s+(\d+)/) { $mylist{$1} = {value => $2, linenum => $. }; } }` [download] You see that instead of just saving off the right-hand value (`$2`) as a scalar value in the (badly-named) hash `%mylist`, the value is a hash-reference which contains the value and the line-number it was found on. You would then access the values along the lines of: `for my $key ( keys %mylist ) { my $value = $mylist{$key}{value}; my $linenum = $mylist{$key}{linenum}; print "$key has value $value, found on line $linenum\n"; }` [download] HTH -- edan	[reply] [d/l] [select]
Re: Line number in a file by ysth (Canon) on Jul 06, 2004 at 09:45 UTC
Newlines aren't important when going through the data. Yes, they are; they determine the line number you say you want :) You are going to have to somehow keep track of them. Are the small parts of $_ you are working with handled consecutively? If so, you can just add up the newlines in each section as you finish working with it: `$linenumber += y/\n//;`	[reply] [d/l]
Re: Line number in a file by Jasper (Chaplain) on Jul 06, 2004 at 10:44 UTC
If you're splitting $_ several times before you get to matching the bit you want, the y/\n//c or matching $` for \n methods aren't going to work. I'd suggest prepending the line number (assuming you haven't changed $\ ;) ) when reading the file: `while (<FILE>) { s/^/[$.]/; $file .= $_; }` [download] then do: `if(/(^\[(\d+)\](\S+)\s+(\d+)/m) { $mylist{$2} = $3; $linenumber = $1; }` [download] Well, that's probably what I'd do (or something like it, anyway - I'd have to see the data to decide)	[reply] [d/l] [select]
Re: Line number in a file by murugu (Curate) on Jul 06, 2004 at 10:28 UTC
if $/(input record separator) is '\n', use $. which is used to get the current line number. for ur problem, use $` and count the number of \n which yields the line number.(But using $` makes program run slow) cheers	[reply]


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