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chop() and chomp()

by Parham (Friar)
on Jan 01, 2002 at 04:23 UTC ( #135462=perltutorial: print w/ replies, xml ) Need Help??

documentation provided for the functions:

------------------------
chomp
This is an alternative to the chop() function. It removes characters at the end of strings corresponding to the $INPUT_LINE_SEPARATOR ($/). It returns the number of characters removed. It can be given a list of strings upon which to perform this operation. When given no arguments, the operation is performed on $_.

chop
This function removes the last character of a string and returns that character. If given a list of arguments, the operation is performed on each one and the last character chopped is returned.
------------------------

these two functions are very much alike... they both remove one (or more) characters from the end of a string... So how are they different you ask? Chomp() ONLY removes new line characters (these are specified in $/), whereas Chop() removes anything that is at the end of the string (it really doesn't care what it is)...

let's demonstrate these two functions:

#chomp() EXAMPLES $a = "abcdefghij"; chomp($a); print $a; #would return exact string... nothing to remove $a = "abcdefghij\n"; chomp($a); print $a; #would return 'abcdefghij', removed newline $a = "abcdefghij\n"; $b = chomp($a); print $b; #would return 1, it did remove something for sure #chop() EXAMPLES $a = "abcdefghij"; chop($a); print $a; #this would return 'abcdefghi' $a = "abcdefghij"; $b = chop($a); print $b; #this would return 'j'
remember.. this with a little bit of usefulness chop() can be the same as chomp()
$a = "abcdefghij\n"; if ($a =~ /\n$/) { chop $a; } #this could also be \r\n if on windows p +latform
most of the time, you'll want to chomp(), but you might want to use chop() with regexes for the same output

Replies are listed 'Best First'.
Re: chop() and chomp()
by davorg (Chancellor) on Jan 02, 2002 at 15:39 UTC
    this could also be \r\n if on windows platform

    Did you try this?

    \n is a logical end of line character which is mapped to the correct physical value by Perl's IO library. If this wasn't true, then porting apps from Unix to Windows would be a lot harder than it currently is.

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

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

Re: chop() and chomp()
by Juerd (Abbot) on Jan 01, 2002 at 22:00 UTC
    perlfunc Describes both chop and chomp, with good examples and excellent detailed explanations.
    I downvoted the tutorial, because it adds nothing to the existing documentation and thus only makes things harder for beginners.

    1. Why did you use $a instead of $_?
    2. print Doesn't return it's given attributes, it returns true if succesful. All your "would return" comments are wrong.
    3. You didn't even chomp arrays or hashes.

    2;0 juerd@ouranos:~$ perl -e'undef christmas' Segmentation fault 2;139 juerd@ouranos:~$

      it wasn't meant as a horribly detailed tutorial. It was meant as a VERY simple tutorial for those that might have not understood why the functions were used. I had it on the computer and i decided to add it to the 'tutorials' section cuz there were no other tutorials on the subject. I didn't use $_ because it might have very well confused those starting out. When in my comment i used 'return', i did not mean literally, i just meant it would 'output' and i feel the need to chomp arrays or hashes cuz again, i wanted it to be a very simple tutorial. I very well understand why you downvoted the tutorial and hope the explanation i gave helped you understand why i wrote it very basically :).
      I'm new to perlmonks (and somewhat to perl) and I hope this acidic comment is an isolated case concerning reactions to people who post useful tutorial tidbits. I for one understood the original post very well. Granted, I think that total newbies might be a bit confused by "print" returning a string. Still, don't you think it's better providing a clarification in a less ...overbearing... tone? :)
Re: chop() and chomp()
by SamCG (Hermit) on Mar 15, 2006 at 18:09 UTC
    I might add the one bit that made me curious (and that I've never really investigated) you didn't really expand on. Specifically, how the function of "$/" works. Admittedly, it's not something one fools with too often, but a bit of explanation may be in order.

    So, I ran some quick tests just to look at what happens when you modify $/. Some of these have implications even when you don't modify $/ -- for example, only one newline will be removed, even if there are two.
    $/='abc'; $_='lafbabc'; chomp; print; ##prints 'lafb', removes 'abc' as expected $_='lafbabcq'; chomp; print; ## prints 'lafbabcq', does not remove embedded 'abc' $_='lafbab'; chomp; print; ## prints 'lafbab', does not remove partial $/ -- 'ab' $_='lafbc'; chomp; print; ## prints 'lafbc', does not remove partial $/ - 'bc' $_='lafabcabc'; chomp; print; ##prints 'lafabc', only removes ONE $/
    Note that the whole string in $/ needs to be present to be considered an "end-of-line" (it doesn't pick out portions of $/), and that it won't remove embedded $/'s.

    These things I think might be helpful to beginners as examples. Also, you might have included the warning about parentheses
    chomp $a, $b; ## this means chomp $a, but leave $b alone! chomp ($a, $b); ## this means chomp both
    I'm going to reserve upvotes/downvotes -- I think you can improve the tutorial considerably and make it worthy of an upvote.

      Be careful with variables named $a and $b, they are special when used in conjunction with sort.

      For example:

      sort { $b cmp $a } @foo;
      gives you an reverse alphabetical (ASCIIbetical really) sort on @foo.


      TGI says moo

Re: chop() and chomp()
by pikablu (Initiate) on May 25, 2007 at 20:39 UTC
    Ah, I get the use of chomp() now, very useful.
      Really good...

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