How to have grep print only the matching text plus X surrounding characters

I need something similar to grep -A and grep -B but for characters. In other words, I have a file with incredibly long lines, e.g.:

[thousands of characters] mytext [thousands of characters]

If I do grep mytext file, I don't want the full lines because it will become way too difficult to read and result in a huge file if I pipe it out to a file. grep -o doesn't work for me because it only returns mytext and I need to see X characters around the match. So imagine a fake option -Y:

$ grep -Y mytext file
Pz8mytextgxe
[email protected]

How do I do this?

If you know Y up front, then you can do e.g.

grep -o '...mytext...' file

where the ... is Y characters long. E.g. the above does for Y=3. The '.' character in a regular expression matches any character.

If you want to find, let's say, from 0 to 10 chars before or after your intended search string, mytext, do this:

grep -rnioE '.{0,10}mytext.{0,10}'

Grep Options Explanation:

1. The -r says to recursively search down the file and folder tree
2. -n says to show line numbers
3. -i says to be case insensitive
4. -o says to only show the matching parts, not the whole line
5. -E says to use Extended regular expressions

Regex Explanation:

See: https://regex101.com/r/BUpUdp/2.

1. . matches any character except newlines
2. {0,10} matches 0 to 10 instances of whatever is before it, which is ., or any character except newlines

Example usage:

I'd like to find any instances of this web page color code (#005cc5) to figure out if it's being used. But, the CSS is literally 5000 lines all on a single line with no line breaks, so I need to only capture a few of the surrounding chars for context--let's say up to 20 before and after. So, I search for grep -rnioE '.{0,20}#005cc5.{0,20}':

$ grep -rnioE '.{0,20}#005cc5.{0,20}'
Test Syntax Highlighting _ GabrielStaples.com home_files/main.css:5:.highlight .l{color:#005cc5}.highlight .n{color
Test Syntax Highlighting _ GabrielStaples.com home_files/main.css:5:.highlight .m{color:#005cc5}.highlight .s{color
Test Syntax Highlighting _ GabrielStaples.com home_files/main.css:5:highlight .mf{color:#005cc5}.highlight .mh{colo
Test Syntax Highlighting _ GabrielStaples.com home_files/main.css:5:r:#005cc5}.highlight .mi{colo
Test Syntax Highlighting _ GabrielStaples.com home_files/main.css:5:r:#005cc5}.highlight .mo{colo
Test Syntax Highlighting _ GabrielStaples.com home_files/main.css:5:r:#005cc5}.highlight .sb{colo
Test Syntax Highlighting _ GabrielStaples.com home_files/main.css:5:highlight .se{color:#005cc5}.highlight .sh{colo
Test Syntax Highlighting _ GabrielStaples.com home_files/main.css:5:highlight .si{color:#005cc5}.highlight .sx{colo
Test Syntax Highlighting _ GabrielStaples.com home_files/main.css:5:highlight .il{color:#005cc5}.gist th,.gist td{b
Test Syntax Highlighting _ GabrielStaples.com home_files/main.css:5:highlight .nb{color:#005cc5}.highlight .nc{colo

Screenshot with coloring:

The second match above shows this color applies to .m CSS classes, for instance, so I can now search the code for any matches using this "m" class, which may show up in some *.html files. (This next search seems to not find everything I want, but you get the idea! The search above works fine.)

grep -rniE 'class="m[\s"]?'