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I thought I was pretty good at regex, but I could never have written this one and had to consult both `man grep` and regex101.com. Explanations for the beginne

I thought I was pretty good at regex, but I could never have written this one and had to consult both `man grep` and regex101.com. Explanations for the beginner and intermediate regex and grep user: `-o`: Only return the match, instead of the entire line `-P`: use Perl compatible regex `-m` max-count, Stop reading a file after NUM matching lines. And now for the regex: `name:`: find the exact match `\s*"`: Zero or more spaces leading up to and including an double quote `\K`: This was the kicker for me. "resets the starting point of the reported match. Any previously consumed characters are no longer included in the final match" - basically tells the regex engine that the characters _before_ `\K` needs to be there in order to form a match, but it should only return the characters _after_ `\K` as the match. This is super handy! Is there a "reverse \K"? `[^"]+`: One or more characters that are not a double quote. This basically means "Find the line that has a key called "name" and return all the characters after the first double quote and until the last double quote"

asicsp 4y ago
If you'd like to learn more about such grep powers, check out my free ebook [0] What do you mean by "reverse \K"? Are you aware of lookarounds? Perhaps you meant positive lookahead? # match digits only if there is a semicolon afterwards $ echo '12; 42,31;100' | grep -oP '\d+(?=;)' 12 31 [0] https://learnbyexample.github.io/learn_gnugrep_ripgrep/introduction.html https://learnbyexample.github.io/learn_gnugrep_ripgrep/intro...
- Joker_vD 4y ago
  Consider this: grep -P 'start: (\d+) end' "How do I make it print only the captured group with the number, not the whole line?" is a pretty common Stack Overflow question. The "\K" thing gets rid of the "start: " part, but what about " end"? That's were "reverse \K" would come in handy.
  - asicsp 4y ago
    That's where lookarounds help: grep -oP 'start: \K\d+(?= end)' `\K` is kinda similar to lookbehind (but not exactly same as it is not zero-width), and particularly helpful for variable length patterns. If you need to process further, you can make use of `-r` option in `ripgrep` or move to other tools like sed, awk, perl, etc.
  - burntsushi 4y ago
    That's where ripgrep's -r/--replace flag comes in handy: $ echo 'foobar start: 123 end quuxbar' | rg 'start: ([0-9]+) end' foobar start: 123 end quuxbar $ echo 'foobar start: 123 end quuxbar' | rg 'start: ([0-9]+) end' -r '$1' foobar 123 quuxbar $ echo 'foobar start: 123 end quuxbar' | rg 'start: ([0-9]+) end' -or '$1' 123
- mxmkm 4y ago
  In vim there is `\zs` and `\ze` where `\zs` is the `\K` equivalent in grep. Basically :%s/hello \zsworld\ze out there/planet/g would find all `hello world out there` and replace `world` to `planet`.
Someone 4y ago
> Is there a "reverse \K"? Look up lookahead and lookbehind (https://www.regular-expressions.info/lookaround.html https://www.regular-expressions.info/lookaround.html, https://perldoc.perl.org/perlre#Extended-Patterns https://perldoc.perl.org/perlre#Extended-Patterns)
darrenf 4y ago
> all the characters after the first double quote and until the last double quote Until the next double quote, not necessarily the last one.

asicsp 4y ago

If you'd like to learn more about such grep powers, check out my free ebook [0] What do you mean by "reverse \K"? Are you aware of lookarounds? Perhaps you meant positive lookahead? # match digits only if there is a semicolon afterwards $ echo '12; 42,31;100' | grep -oP '\d+(?=;)' 12 31 [0] https://learnbyexample.github.io/learn_gnugrep_ripgrep/introduction.html https://learnbyexample.github.io/learn_gnugrep_ripgrep/intro...

Joker_vD 4y ago
Consider this: grep -P 'start: (\d+) end' "How do I make it print only the captured group with the number, not the whole line?" is a pretty common Stack Overflow question. The "\K" thing gets rid of the "start: " part, but what about " end"? That's were "reverse \K" would come in handy.
- asicsp 4y ago
  That's where lookarounds help: grep -oP 'start: \K\d+(?= end)' `\K` is kinda similar to lookbehind (but not exactly same as it is not zero-width), and particularly helpful for variable length patterns. If you need to process further, you can make use of `-r` option in `ripgrep` or move to other tools like sed, awk, perl, etc.
- burntsushi 4y ago
  That's where ripgrep's -r/--replace flag comes in handy: $ echo 'foobar start: 123 end quuxbar' | rg 'start: ([0-9]+) end' foobar start: 123 end quuxbar $ echo 'foobar start: 123 end quuxbar' | rg 'start: ([0-9]+) end' -r '$1' foobar 123 quuxbar $ echo 'foobar start: 123 end quuxbar' | rg 'start: ([0-9]+) end' -or '$1' 123
mxmkm 4y ago
In vim there is `\zs` and `\ze` where `\zs` is the `\K` equivalent in grep. Basically :%s/hello \zsworld\ze out there/planet/g would find all `hello world out there` and replace `world` to `planet`.

Someone 4y ago

> Is there a "reverse \K"? Look up lookahead and lookbehind (https://www.regular-expressions.info/lookaround.html https://www.regular-expressions.info/lookaround.html, https://perldoc.perl.org/perlre#Extended-Patterns https://perldoc.perl.org/perlre#Extended-Patterns)

darrenf 4y ago

> all the characters after the first double quote and until the last double quote Until the next double quote, not necessarily the last one.