I'd like to search for text that may be split over several lines in a file. A grep that would ignore line breaks and return the matching span of lines.

e.g. I would be searching for is an example file, and expect it to be found in the following file:

This is
example file.

Not to depend on leading or trailing spaces, entirely ignoring all forms of white space might be best (ideally, treating any sequence of white space as a single space).

One non-ideal solution is tr '\n' ' ' | grep, that discriminates between matches and non-matches, but doesn't show the match, nor deals well with big files.

  • on SO (no definitive answer) : stackoverflow.com/q/1858312/1449460 – Nikana Reklawyks May 18 '15 at 17:26
  • As a side note, emacs' search seems to do the job (isearch-forward) – Nikana Reklawyks May 18 '15 at 17:33
  • So does Vim's: /This\_sis. For more details: :help \_s. – lcd047 May 18 '15 at 17:37
  • Add this line at the end of your search line: tr -n "\n" This will remove all new lines. Hope this help! – Dan Howel Aug 18 '17 at 18:28

The GNU grep can do it

grep -z 'is\san\sexample\sfile.' file

To fulfill some points which arise in comments there are some modifications to script:

 grep -oz '^[^\n]*\bis\s*an\s*example\s*file\.[^\n]*' file

Regarding huge files I have no imagination of memory limitation but in the case of problem you are free to use sed

sed '/\bis\b/{
     D' file

that keep no more than 4-lines (because 4 words in pattern) in memory (\(\n.*\)\{3\}).

| improve this answer | |
  • 5
    As I’m sure you know, the -z option tells grep to treat newlines as ordinary text characters, and look for nul bytes to separate records.  In a text file with no nul bytes (i.e., the typical case), grep -z will treat the entire file as one line.  So (1) this raises the question of how well it can handle large files, and (2) if it finds a match, it will write out the entire file, giving no clue as to the location of the match.  Also (3) the OP said, “ideally, treating any sequence of white space as a single space,” so you should use \s+ and add -E. – G-Man Says 'Reinstate Monica' May 18 '15 at 23:38
  • 1
    @G-Man Thank you for comment. Please see edited answer. – Costas May 19 '15 at 9:28
  • 1
    (0) Ah, -o; I keep forgetting about that.  Clever way to use it.  (1) Your new grep answer begins ^[\n]*; that’s a typo for [^\n]*.  (2) I said \s+ deliberately.  be\s*little will match belittle, and care\s*less will match careless.  But I guess that’s a minor problem.  And, if you don’t want to use -E, you can use “the poor man’s version” of \s+, namely, \s\s*.  (3) Nice sed command.  It can fail if there are blank lines (so the four-word phrase can spread over more than four lines); I was able to fix that by adding s/\n\s*\n/\n/. – G-Man Says 'Reinstate Monica' May 20 '15 at 1:10
  • @G-Man Thank you againg. Your comments are very useful. I have try to post more or less portable code because famous members everytime push me to do so. Anyway even without -E you steel able to use + in \s\+ form. Empty lines inside of pattern seems to be a contrived. – Costas May 20 '15 at 8:55
  • I was thinking of paginated text documents, like RFCs — ISTR that man pages look like that on some systems (or did) — but, on further thought, it occurs to me that most such documents have page header(s) and/or footer(s) that would need to be stripped out before you could hope to grep them for phrases. – G-Man Says 'Reinstate Monica' May 20 '15 at 16:44

Try this:

pcregrep -M '\bThis\s+is\b' <<EOT
an example
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  • Do I have to type \s 5 times if I search for "this is a very long pattern" ? – Nikana Reklawyks May 18 '15 at 17:31
  • 1
    Yes: the point is \s matches spaces, and newline is a "space". – lcd047 May 18 '15 at 17:32
  • I mean, what if the file is This\nis a very\nlong pattern, and I don't know where the line breaks might occur. I'd have to search for This\sis\sa\svery\slong\spattern, right ? (which becomes tedious as the length of the pattern increases or is pasted from elsewhere) – Nikana Reklawyks May 18 '15 at 17:36
  • 2
    Then you do it like this: pcregrep -M "$( echo 'This is a very long pattern' | sed 's/ /\\s+/g' )" file. – lcd047 May 18 '15 at 17:46

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