ruby print selected lines of text in between 2 strings

Question

i'm trying to get a group of text in between 2 strings in ruby, and i can't seem to get the right method or use the right regex.

text:

<html>
<body>

<!-- begin posts --> 

<h1>all kinds of html<h1>
<p> blah blah </p>
<p> i've been working on this forever </p>

<!-- end posts --> 

</html>
</body>

and i just want to get everything from  to , inclusive, and save that block of text in a text file.

i figured out how to print the line in the beginning:

File.open("index.html").each_line do |line|
body.each {|line| puts line if line =~ /<!-- begin/}

but not the lines after up and until the last string.

i have a rubular here http://rubular.com/r/0W9QDpMGkM where i haven't been able to figure out anything.

thanks everyone in advance.

FYI, a better option for your use case may be to use ERB, see the examples in this answer: http://stackoverflow.com/questions/980547/how-do-i-execute-ruby-template-files-erb-without-a-web-server-from-command-line — Abdullah Jibaly, Jul 09 '11 at 04:50
that looks really great. i'm going to try to explore it a little. thank you. — rick, Jul 09 '11 at 05:02

mu is too short · Accepted Answer · 2011-07-09T05:48:33.557

8

Don't do it line by line, just slurp the whole thing into a string and rip it apart:

s    = File.read('index.html')
want = s.match(/<!-- begin posts -->(.*)<!-- end posts -->/m)[1]

And now everything between your markers is in want. Don't forget the m modifier on the regex.

While you're mangling your input you can strip out the stray leading and trailing whitespace too:

want = s.match(/<!-- begin posts -->(.*)<!-- end posts -->/m)[1].strip

As Tudor notes below, you might want to use a non-greedy (.*?) for the group if you think there is any chance of multiple  markers; doesn't hurt to be a little paranoid when they really are you to get you.

References:

UPDATE: the match method on a string returns a MatchData object. The array access operator:

... mtch[0] is equivalent to the special variable $&, and returns the entire matched string. mtch[1], mtch[2], and so on return the values of the matched backreferences (portions of the pattern between parentheses).

Is used to access the matching parts. There's only one group in the regex so [1] gets you the contents of that group without the surrounding HTML comment delimiters.

edited Jul 09 '11 at 05:48

answered Jul 09 '11 at 04:55

mu is too short

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@mu_is i literally had this same code without the [1] on the end. can you explain that? – rick Jul 09 '11 at 04:58
@rick: I added (another) update with some notes on what `match` returns and what the `[1]` is for. – mu is too short Jul 09 '11 at 05:04
@mu_is thanks! is there an easy way to include the strings in the regex so they are included in the "#{want}" ? – rick Jul 09 '11 at 05:11
@rick: The whole thing will be in `[0]`: "... `mtch[0]` is equivalent to the special variable `$&`, and returns the entire matched string." – mu is too short Jul 09 '11 at 05:27
1

@mu - you might want to have `.*?` instead of `.*` for the case there are multiple `` tags in the same page – Tudor Constantin Jul 09 '11 at 05:44
@Tudor: True enough, I added some notes to that effect. It is getting late over here :) – mu is too short Jul 09 '11 at 05:49

Tudor Constantin · Answer 2 · 2011-07-09T05:42:07.767

3

try with:

printing = false
File.open("index.html").each_line do |line|
  printing = true if line =~ /<!-- begin/      
  puts line if printing
  printing = false if line =~ /<!-- end posts/
end

edited Jul 09 '11 at 05:42

answered Jul 09 '11 at 04:50

Tudor Constantin

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this is giving me `syntax error, unexpected $end, expecting kEND` – rick Jul 09 '11 at 04:59
You could use the flip flop operator here. Then again, it [isn't commonly used](https://github.com/rubinius/rubinius/issues/1006), so the next person reading it may get confused. – Andrew Grimm Jul 09 '11 at 13:56

score 0 · Answer 3 · answered Mar 21 '14 at 17:00

0

File.readlines(ARGV[0]).each do|line|
  if line =~ /<!-- begin posts -->/ .. line =~ /<!-- end posts -->/     
    puts line
  end
end

answered Mar 21 '14 at 17:00

Sanjeev

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ruby print selected lines of text in between 2 strings

3 Answers3

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