Non greedy matching using ? with grep

Question

I'm writing a bash script which analyses a html file and I want to get the content of each single <tr>...</tr>. So my command looks like:

$ tr -d \\012 < price.html | grep -oE '<tr>.*?</tr>'

But it seems that grep gives me the result of:

$ tr -d \\012 < price.html | grep -oE '<tr>.*</tr>'

How can I make .* non-greedy?

The obligatory: [You can't parse html with regular expressions](http://stackoverflow.com/a/1732454/7552) — glenn jackman, Oct 01 '13 at 21:06

Chris Seymour · Accepted Answer · 2015-12-27T14:06:31.483

18

If you have GNU Grep you can use -P to make the match non-greedy:

$ tr -d \\012 < price.html | grep -Po '<tr>.*?</tr>'

The -P option enables Perl Compliant Regular Expression (PCRE) which is needed for non-greedy matching with ? as Basic Regular Expression (BRE) and Extended Regular Expression (ERE) do not support it.

If you are using -P you could also use look arounds to avoid printing the tags in the match like so:

$ tr -d \\012 < price.html | grep -Po '(?<=<tr>).*?(?=</tr>)'

If you don't have GNU grep and the HTML is well formed you could just do:

$ tr -d \\012 < price.html | grep -o '<tr>[^<]*</tr>'

Note: The above example won't work with nested tags within <tr>.

edited Dec 27 '15 at 14:06

answered Oct 01 '13 at 20:25

Chris Seymour

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The last example (using "[^<]*" is unlikely to work since there will inevitably be "td" or "th" tags within "tr". – glenn jackman Oct 01 '13 at 21:05
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@glennjackman good point, I will leave it in the answers however as the general principle might be useful to on lookers. – Chris Seymour Oct 01 '13 at 21:10

tripleee · Answer 2 · 2018-11-19T06:09:49.980

Non-greedy matching is not part of the Extended Regular Expression syntax supported by grep -E. Use grep -P instead if you have that, or switch to Perl / Python / Ruby / what have you. (Oh, and pcregrep.)

Of course, if you really mean

<tr>[^<>]*</tr>

you should say that instead; then plain old grep will work fine.

You could (tediously) extend the regex to accept nested tags which are not <tr> but of course, it's better to use a proper HTML parser than spend a lot of time rediscovering why regular expressions are not the right tool for this.

score 3 · Answer 3 · answered Oct 01 '13 at 20:25

3

.*? is a Perl regular expression. Change your grep to

grep -oP '<tr>.*?</tr>'

answered Oct 01 '13 at 20:25

ThisSuitIsBlackNot

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Or, if he only wants the contents of the tr tag: `grep -oP '(?<=).*?(?=)'` -- using look-arounds to omit the actual tags – glenn jackman Oct 01 '13 at 20:42

score 3 · Answer 4 · answered Oct 01 '13 at 20:25

3

Try perl-style-regexp

$ grep -Po '<tr>.*?</tr>' input
<tr>stuff</tr>
<tr>more stuff</tr>

answered Oct 01 '13 at 20:25

Fredrik Pihl

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Non greedy matching using ? with grep

4 Answers4