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


I started using Regexp recently.

Here is my Input:


what is the correct regexp to use to get these columns delimited into 19 columns out of which columns 14,15,16,17 are null?


Replies are listed 'Best First'.
Re: Regexp help
by frozenwithjoy (Priest) on Nov 22, 2012 at 01:02 UTC
    Why not use split?
    $ perl -E '$string = "0.740234|0.758789|0.748047|0.749023|0.748047|0.7 +54883|0.743164|0.748047|0.780273|0.739258|0.765625|0.761719|0.760742| +||||0.75293|0.742188"; say $_ for (split /\|/, $string); ' 0.740234 0.758789 0.748047 0.749023 0.748047 0.754883 0.743164 0.748047 0.780273 0.739258 0.765625 0.761719 0.760742 0.75293 0.742188

    NOTE: Keep in mind that when matching | in split (or another regex situation), you need to escape it: \|

Re: Regexp help
by 2teez (Vicar) on Nov 22, 2012 at 01:09 UTC

    split perl function will conveniently do like so:

    use warnings; use strict; use Data::Printer; my $str='0.740234|0.758789|0.748047|0.749023|0.748047|0.754883|0.74316 +4|0.748047|0.780273|0.739258|0.765625|0.761719|0.760742|||||0.75293|0 +.742188'; my @str_data = split/\|/,$str; p @str_data;
    [ [0] 0.740234, [1] 0.758789, [2] 0.748047, [3] 0.749023, [4] 0.748047, [5] 0.754883, [6] 0.743164, [7] 0.748047, [8] 0.780273, [9] 0.739258, [10] 0.765625, [11] 0.761719, [12] 0.760742, [13] "", [14] "", [15] "", [16] "", [17] 0.75293, [18] 0.742188 ]

    If you tell me, I'll forget.
    If you show me, I'll remember.
    if you involve me, I'll understand.
    --- Author unknown to me
Re: Regexp help
by muba (Priest) on Nov 22, 2012 at 01:23 UTC

    First of all, what do you mean by null? I will assume you mean undef, but you might as well mean the numerical value 0.

    Secondly, one of Perl's slogan's is There Is More Than One Way To Do It, or TIMTOWTDI as we say. This applies here as well. There is no the correct way, there are many.

    My next question, thus, is: what have you tried? Why didn't it work? Did you get any error messages and if you did, which? How did your output not meet your expectations?

    Lastly, a regular expression in the traditional sense (m//) might not b the most suitable task. What you have is a | delimited string, so most likely you'll want to split on that. Keep in mind that split takes a regular expression as its first argument, and | has a special meaning inside regular expression so you'll have to escape that.

    Then you'll want to iterate over the list you get, using something like map for example, or if you're uncomfortable with those merits of functional programming, you could do it with a simple foreach loop over the array.

    This should give you the building blocks you're looking for.

      Thank you.

      the back ground is I am using regexp in sql (not really perl this time)

      I tried the following:

      REGEXP_SUBSTR({total},'^*', 1, 1) where total is the input string

      I result I am getting is its not recongizing the empty (or null) columns.