How to give a pattern for new line in grep?

Question

How to give a pattern for new line in grep? New line at beginning, new line at end. Not the regular expression way. Something like \n.

Anjanetteanjela

It's not clear what you want. new line at the beginning is a blank line and new line at end applies to every line in the file. Can you post an example? – Sequent

Actually you can just use $. It's somewhat limited, but usable in simple cases. – Armenta

gnu.org/software/grep/manual/grep.html#Usage see item 15. – Despite

Answer 1

grep patterns are matched against individual lines so there is no way for a pattern to match a newline found in the input.

However you can find empty lines like this:

grep '^$' file
grep '^[[:space:]]*$' file # include white spaces 

Gog

At least GNU grep has -z option that makes grep break lines by null character. However, it does not seem to support newline or \n in pattern to match newline, see bug report. – Despite

@Despite It supports \n in patterns with the -P flag – Monas

Answer 2

try pcregrep instead of regular grep:

pcregrep -M "pattern1.*\n.*pattern2" filename

the -M option allows it to match across multiple lines, so you can search for newlines as \n.

Wilkerson

This is an excellent suggestion. I've used pcregrep a LOT the last week. For example, pcregrep -lMr "\r\n" * to recursively find all files that have at least one CRLF line ending. And after conversion to Unix line endings, I used pcregrep -lMr " \n" * to find all files having Markdown soft line breaks. Very helpful! – Gynous

This is the most efficient of all the answers, trying to accomplish this with grep made me waste a day. – Inflectional

Answer 3

Thanks to @jarno I know about the -z option and I found out that when using GNU grep with the -P option, matching against \n is possible. :)

Example:

grep -zoP 'foo\n\K.*'<<<$'foo\nbar'

Result:

bar

Example that involves matching everything including newlines:

.* will not match newlines. To match everything including newlines, use¹ (.|\n)*:

grep -zoP 'foo\n\K(.|\n)*'<<<$'foo\nbar\nqux'

Result:

bar
qux

¹ Seen here: https://stackoverflow.com/a/33418344

Monas

Great, note that I do not get notification about the "@jarno" in the answer. – Despite

This is great! Thank you so much for sharing! – Bysshe

Works for me. Thanks a lot. grep -zoPnir "dex\n035" ./dir/ – Ferrigno

Answer 4

You can use this way...

grep -P '^\s$' file

• -P is used for Perl regular expressions (an extension to POSIX grep).
• \s match the white space characters; if followed by *, it matches an empty line also.
• ^ matches the beginning of the line. $ matches the end of the line.

Lulu

-P is a GNU extension. I am fine for using it when the situation calls for it (typically lookahead/lookbehind), but POSIX grep can do this just file with [[:space:]]. – Dyeline

FWIW, Solaris' and BSD's grep manpages (didn't check others) both have a paragraph for -P. GNU is quite standard anyway. :) – Scenography

From manual page: [-P] This option is not supported in FreeBSD. – Poddy

No [-P] for MacOsX either: grep [-abcdDEFGHhIiJLlmnOopqRSsUVvwxZ] [-A num] [-B num] [-C[num]] [-e pattern] [-f file] [--binary-files=value] [--color[=when]] [--colour[=when]] [--context[=num]] [--label] [--line-buffered] [--null] [pattern] [file ...] – Habiliment

@Niccolò You'll want to brew install grep to get GNU grep, which is superior in several ways. apple.stackexchange.com/questions/193288/… – Gilbertogilbertson

Answer 5

As for the workaround (without using non-portable -P), you can temporary replace a new-line character with the different one and change it back, e.g.:

grep -o "_foo_" <(paste -sd_ file) | tr -d '_'

Basically it's looking for exact match _foo_ where _ means \n (so __ = \n\n). You don't have to translate it back by tr '_' '\n', as each pattern would be printed in the new line anyway, so removing _ is enough.

Papandreou

pardon my ignorance, but is using process substituion not yet another NON posix compatible, hence non-portable feature? in posix shell I could not do <(p paste -sd_ file )? – Rafaello

Answer 6

just found

grep $'\r'

It's using $'\r' for c-style escape in Bash.

in this article

Butane

carriage return \r is not a newline \n. If your grepping for windows style line ending you need \r\n – Spermatic