3

Assume we have the following test.txt:

# commented line, no match
# commented line, would match /app/
# again commented, would match app
non commented line, matchin /app
non commented line, no match

I would like to get all lines that contain the word 'app', - but not those that have a comment, - and I would like the filename to be output.

The trivial grep -H 'app' test.txt, obviously, matches everything and does not avoid lines starting with number/hash character #:

term1.png

A pipeline with a second grep with -v, --invert-match option generally messes up the colors, and to preserve the -H filenames, I would not be able to specify a negated match for ^# (i.e. a number/hash character at the start of a line) so I'd have to use a beast like grep -H app test.txt --color=always | grep -v '\[K:.\[m.\[K#' to preserve colors:

term2.png

... but only after doing something like grep -H app test.txt --color=always | hexdump -C so I can see the right combo of characters, which is, mildly speaking, tedious.

And unfortunately, seemingly one cannot use the -v option to specify its own (negated) pattern in a combo with -e PATTERN, --regexp=PATTERN option which can specify multiple search patterns:

:tmp$ grep -H -e 'app' -v '^#' test.txt
grep: ^#: No such file or directory
test.txt:# commented line, no match
test.txt:non commented line, no match
test.txt:

Here, grep interprets '^#' to be a filename, not a search pattern - so the -v inverts the matching of app, and I get the wrong results from the expected one. Otherwise, in this example, the expected output is only one line:

test.txt:non commented line, matchin /app

... with properly colored filename, and matches.

So, is there a way to achieve this - but without the messy pipeline given above, and simply using ^# as the pattern to be avoided?

  • 1
    @Theophrastus that's a good idea I think - except it won't match the pattern app if it happens to be at the very start of the line: perhaps match a word boundary or any character except # e.g. grep -HE --color=always '^(\b|[^#]).*app'? – steeldriver Dec 11 '15 at 3:41
  • Something similar, via unix.stackexchange.com/questions/70710 and PCRE negative look-ahead: the following command matches only lines that do not start with any ammount of whitespace followed by //, but contain the word myword: grep -rnP '^(?![[:space:]]*//).*myword' --include='*.cxx' – sdaau Jan 5 at 21:14
5
grep -E '^([^#].*)?app' ./infiles* /dev/null

I guess the comments already nearly had it anyway, but if you make the head of line [^#] not-comment match ?optional, then you either get lines that begin with the match app or you get lines which begin with something else and then eventually match app - but either way, you don't get lines that begin with #.

Regarding the colors - well... that depends on the grep and the regexp, but a standard GNU grep should highlight the whole match up to the last app match. If you would like it more specific you can do info grep to have a look at what environment vars a GNU grep will consider when highlighting and configure them appropriately , or, failing a satisfactory result in that vein, highlight it yourself.

  • Many thanks @mikeserv and the comments - this works, just note that in my example, the entire line is highlighted, as this answer also warns about. Cheers! – sdaau Dec 11 '15 at 9:32

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.