Databases
StackOverflow2013
Postsdbo
POWhy does this regex run differently in sed than in Perl/Ruby?
 

Note that there are some explanatory texts on larger screens.

plurals
  1. POWhy does this regex run differently in sed than in Perl/Ruby?
    primarykey
    data
    text
    <p>I have a regex that gives me one result in <code>sed</code> but another in Perl (and Ruby).</p> <p>I have the string <code>one;two;;three</code> and I want to highlight the substrings delimited by the <code>;</code>. So I do the following in Perl:</p> <pre><code>$a = "one;two;;three"; $a =~ s/([^;]*)/[\1]/g; print $a; </code></pre> <p>(Or, in Ruby: <code>print "one;two;;three".gsub(/([^;]*)/, "[\\1]")</code>.)</p> <p>The result is:</p> <pre><code>[one][];[two][];[];[three][] </code></pre> <p>(I know the reason for the spurious empty substrings.)</p> <p>Curiously, when I run the same regexp in <code>sed</code> I get a different result. I run:</p> <pre><code>echo "one;two;;three" | sed -e 's/[^;]*/[\0]/g' </code></pre> <p>and I get:</p> <pre><code>[one];[two];[];[three] </code></pre> <p>What is the reason for this different result?</p> <p>EDIT:</p> <p>Somebody replied "because <code>sed</code> is not <code>perl</code>". I know that. The reason I'm asking my question is because I don't understand how <code>sed</code> copes so well with zero-length matches.</p>
    singulars
    1. PO
      singulars
      1. PTAnswer
    1. This table or related slice is empty.
    1. PTQuestion
    1. USsteenslag
    1. USNiccolo M.
    plurals
    1. This table or related slice is empty.
    1. This table or related slice is empty.
    1. This table or related slice is empty.
    1. PO
      singulars
      1. PTAnswer
    2. PO
      singulars
      1. PTAnswer
    3. PO
      singulars
      1. PTAnswer
    1. VO
      singulars
      1. POWhy does this regex run differently in sed than in Perl/Ruby?
      1. This table or related slice is empty.
      1. VTUpMod
    2. VO
      singulars
      1. POWhy does this regex run differently in sed than in Perl/Ruby?
      1. This table or related slice is empty.
      1. VTUpMod
    3. VO
      singulars
      1. POWhy does this regex run differently in sed than in Perl/Ruby?
      1. This table or related slice is empty.
      1. VTUpMod
    1. CO`sed` doesn't *"cope ... well with zero-length matches"* - it gets it wrong in a way that happens to do what you need. Write `join ';', map "[$_]", split /;/, $str` instead and don't use `a` as an identifier.
      singulars
      1. POWhy does this regex run differently in sed than in Perl/Ruby?
      1. USBorodin
    2. COI cannot answer the question due to my lack of knowledge about perl& ruby. however this is a good question. just was asked not in a right way... **+1** anyway... wait to learn how did perl/ruby handle the `greedy` matching.
      singulars
      1. POWhy does this regex run differently in sed than in Perl/Ruby?
      1. USKent
    3. CO@mirabilos: thanks; I was already aware of a way to get rid of the empty substrings. It wasn't the thing that bothered me.
      singulars
      1. POWhy does this regex run differently in sed than in Perl/Ruby?
      1. USNiccolo M.
 

Querying!

 
Guidance
A row detail

Detail views are divided into sections. All the information in the data section comes from columns in the selected row. The other sections display data from other, related rows.

Related data can be related in a to-one or a to-many fashion. Captions of data related in a to-many fashion link to a list view showing a filtered view of the table.

Try moving around until you find a non-empty to-many entry and click on the label to get to one. You can move back to the root by clicking on the database name in the header.

SQuiL has stopped working due to an internal error.

If you are curious you may find further information in the browser console, which is accessible through the devtools (F12).

Reload