Use grep for a long line to get the part of the line

Question

I want to search in a long sentence (more than 1024 letters).

I have one text file (test.txt) which has one long sentence, like this:

afdafglwqgkjrldjl;ewqje;'k;g;je;;;fdsgalsdkf;akslg;safdas.....dasfsd

Now I want to check which line contains the word saf. This command just shows the whole sentence:

less test.txt | grep saf

Is it possible to get a part of the sentence or should I use a command other than grep?

THanks! It shows the matched point. however is it possible to show the a few letters before and after of matches??? — whitebear, Oct 19 '18 at 14:56
grep -o '.\{0,3\}saf.\{0,3\}' text.text – this will include up to three characters before and up to three characters after. But if there is a second saf and it begins within these "three characters after" then it won't be matched separately. — Kamil Maciorowski, Oct 19 '18 at 15:48
@KamilMaciorowski It's perfect what I want. it works prety well — whitebear, Oct 23 '18 at 21:44
Related: https://stackoverflow.com/questions/2034799/how-to-truncate-long-matching-lines-returned-by-grep-or-ack — Ciro Santilli OurBigBook.com, Oct 10 '23 at 07:12

t0r0X · Answer 1 · 2018-10-24T00:52:41.410

6

Not exactly what you were looking for: show the matching lines and highlight the occurences in those lines:

grep --color 'saf' test.txt

Options for searching saf and displaying up to 15 characters before and after the occurences found using:

the standard regex syntax, first mentioned by @kamil-maciorowski in his comment on the question:
```
grep -o '.\{0,15\}saf.\{0,15\}' test.txt | grep saf --color
```

Perl-compatible regex syntax with the -P option, if available:

grep -o -P '.{0,15}saf.{0,15}' test.txt | grep --color saf

extended regex syntax with the -E option, if your grep has no -P option (like e.g. on macOS):
```
grep -o -E '.{0,15}saf.{0,15}' test.txt | grep --color saf
```

edited Oct 24 '18 at 00:52

answered Oct 19 '18 at 15:36

t0r0X

See my comment under the question. If you add a remark to your answer about a possibility of not matching all saf-s, I will upvote it and delete my comment. – Kamil Maciorowski Oct 19 '18 at 15:53
Thanks @t0r0X , I tried your one too . my grep doens't have -P option somehow. and backslash before { is needed. But I appreciate your answer too. – whitebear Oct 23 '18 at 21:46
@whitebear Indeed, not every grep has -P, but there's yet another variant, I'll update again my answer. – t0r0X Oct 24 '18 at 00:33
@kamil-maciorowski I will look into it. – t0r0X Oct 24 '18 at 16:04
This is super useful for grepping on minified files. – John Churchill Feb 09 '21 at 20:11

Ciro Santilli OurBigBook.com · Answer 2 · 2023-10-10T07:39:22.037

bgrep if lines don't necessarily fit into memory

I keep coming back to this random repo from time to time: https://github.com/tmbinc/bgrep Install:

curl -L 'https://github.com/tmbinc/bgrep/raw/master/bgrep.c' | gcc -O2 -x c -o $HOME/.local/bin/bgrep -

Use:

bgrep `printf %s saf | od -t x1 -An -v | tr -d '\n '` myfile.bin

Sample output:

myfile.bin: c80000003
\x02abc
myfile.bin: c80000007
dabc

I have tested it on files that don't fit into memory, and it worked just fine.

2 Answers2