Comments on: Explantion on the use of chop() and chomp() functions.

By: crz

crz — Thu, 03 Sep 2009 04:56:48 +0000

Thanks Chas for pointing out. i made some revisions. I believe now the explanation is correct. But please check, if there is still corrections to be done, I’ll.

By: Chas. Owens

Chas. Owens — Thu, 03 Sep 2009 04:38:58 +0000

My point is that you are claiming that the readline operator is adding a newline to the string, and that claim is wrong. The newline is already there.

By: crz

crz — Thu, 03 Sep 2009 03:57:45 +0000

yes, you are right. chomp() removes what is declared in ‘$/’ while chop() removes the last character.

By: crz

crz — Thu, 03 Sep 2009 03:56:24 +0000

exactly, that is what I said when I said If we explicitly assign ‘f’ to ‘$/’ the line will end where it first sees a n ‘f’.

By: Andrew

Andrew — Thu, 03 Sep 2009 03:20:33 +0000

Chop isn’t really “better”. If you’re using <> you should always be using chomp with it, because they both use $/ in the same way. <> reads everything up to and including the record separator, and chomp removes the record separator. If you use chomp, your code will do the right thing whether $/ is “\n” or “\r\n” or “\n–\n” or \4096. If you use chop, it won’t always work.

By: Chas. Owens

Chas. Owens — Wed, 02 Sep 2009 19:53:18 +0000

Drat the lack of a preview option. All of my angle brackets were interpreted as HTML. Here it is again with entities instead:

The input record separator ($/) does in fact contain “\n” by default. That is why the readline operator (<>) returns lines, but the readline operator does not add “\n” to lines. That character is already part of the line in the file you are reading from. STDIN is no different from any other file. Pressing enter is not some magic thing that cause Perl to read the line. Pressing enter generates a newline. Perl sees the newline (just like it sees every character), compares it to what is currently set in $/, sees that they are the same, so it returns the string including the “\n” that you — not the readline operator — put there.

If you were to set the input record separator to “\n===\n” then it would return a multi-line string that ends with “\n===\n” (or the entire file if it doesn’t contain “\n===\n”). Try this on the commandline:

perl -e ‘$/ = “\n===\n”; my $record = ; print “I saw: $record”‘

Type as much as you want, hit enter as many times as you want. Then (after hitting enter) type === and hit enter. The program will print back what you typed.

By: Chas. Owens

Chas. Owens — Wed, 02 Sep 2009 19:50:48 +0000

The input record separator ($/) does in fact contain “\n” by default. That is why the readline operator () returns lines, but the readline operator does not add “\n” to lines. That character is already part of the line in the file you are reading from. STDIN is no different from any other file. Press enter is not some magic thing that cause Perl to read the line. Pressing enter generates a newline. Perl sees the newline (just like it sees every character), compares it to what is currently set in $/, sees that they are the same, so it returns the string including the “\n” that you — not the readline operator — put there.

perl -e ‘$/ = “\n===\n”; my $record = ; print “I saw: $record”‘

Type as much as you want, hit enter as many times as you want. Then (after hitting enter) type === and hit enter. The program will print back what you typed.

By: crz

crz — Wed, 02 Sep 2009 18:41:54 +0000

I’m not completely aware of what you have said as I’m still learning. Anyway I assume confirms that you have entered the input once you have enter the return key.
However I ran the below code and it is outputting a new line so what I said should be correct
#!/usr/bin/perl print $/;
But I’ll read the documentation and look into it deeper and change the post if there is anything wrong.
Anyway thanks for dropping in.

By: Chas. Owens

Chas. Owens — Wed, 02 Sep 2009 14:56:13 +0000

It is import to note that is not adding the newlines, it is not stripping them. They are already in the file being read (in this case they are put there by your hitting the enter key). You can see the behavior clearly in this sample code:

perl -e ‘print “foo\nbar\nbaz”‘ | perl -ne ‘s/\n/CR/;print “[$_]\n”‘

The last line does not have a newline character, and it does not show up in the output.

By: crz

crz — Wed, 02 Sep 2009 11:16:34 +0000

Thanks for noticing, Corrected. Yeah, I’ll look into the documentation.