Hi everyone !

I’m in need for some assistance for string manipulation with sed and regex. I tried a whole day to trial & error and look around the web to find a solution however it’s way over my capabilities and maybe here are some sed/regex gurus who are willing to give me a helping hand !

With everything I gathered around the web, It seems it’s rather a complicated regex and sed substitution, here we go !

What Am I trying to achieve?

I have a lot of markdown guides I want to host on a self-hosted forgejo based git markdown. However the classic markdown links are not the same as one github/forgejo…

Convert the following string:

[Some text](#Header%20Linking%20MARKDOWN.md)

Into

[Some text](#header-linking-markdown.md)

As you can see those are the following requirement:

  • Pattern: [Some text](#link%20to%20header.md)
  • Only edit what’s between parentheses
  • Replace space (%20) with -
  • Everything as lowercase
  • Links are sometimes in nested parentheses
    • e.g. (look here [Some text](#link%20to%20header.md))
  • Do not change a line that begins with https (external links)

While everything is probably a bit complex as a whole the trickiest part is probably the nested parentheses :/

What I tried

The furthest I got was the following:

sed -Ei 's|\(([^\)]+)\)|\L&|g' test3.md #make everything between parentheses lowercase

sed -i '/https/ ! s/%20/-/g' test3.md #change every %20 occurrence to -

These sed/regx substitution are what I put together while roaming the web, but it has a lot a flaws and doesn’t work with nested parentheses. Also this would change every %20 occurrence in the file.

The closest solution I found on stackoverflow looks similar but wasn’t able to fit to my needs. Actually my lack of regex/sed understanding makes it impossible to adapt to my requirements.

I would appreciate any help even if a change of tool is needed, however I’m more into a learning processes, so a script or CLI alternative is very appreciated :) actually any help is appreciated :D !

Thanks in advance.

  • learnbyexample@programming.devEnglish
    2·
    3 days ago

    Here’s a solution with perl (assuming you don’t want to change http/https after the start of ( instead of start of a line):

    perl -pe 's/\[[^]]+\]\(\K(?!https?)[^)]+(?=\))/lc $&=~s|%20|-|gr/ge' ip.txt
    • e flag allows you to use Perl code in the substitution portion.
    • \[[^]]+\]\(\K match square brackets and use \K to mark the start of matching portion (text before that won’t be part of $&)
    • (?!https?) don’t match if http or https is found
    • [^)]+(?=\)) match non ) characters and assert that ) is present after those characters
    • $&=~s|%20|-|gr change %20 to - for the matching portion found, the r flag is used to return the modified string instead of change $& itself
    • lc is a function to change text to lowercase
    • N0x0n@lemmy.mlOP
      1·
      3 hours ago

      Sorry for the late response… I was busy with another user :S My English is so bad I’m not able to response to every one at the same time… Whatever…

      I tried your pearl regex substitution and effectively it does what I ask from my post, so thank you very much for your help ! However, I missed a few use cases were your regex breaks… But that’s on me, your command works as expected !!!

      [Link with numbers](Another%20Markdown%20file.md#1.3%20this%20is%20another%20test.md)

      The part before the hashtag need to keeps it’s original form (even with %20) because it links to a markdown file directly and not a header (Hope it’s comprehensible?). It took me a lot of time with another user and we came to a wrapped up script that does everything:

      #! /bin/bash

files="/home/USER/projects/test.md"

mdlinks="$(grep -Po ']\((?!https).*\)' "$files")"
mdlinks2="$(grep -Po '#.*' <<<$mdlinks)"

while IFS= read -r line; do
	#Converts 1.2 to 1-2 (For a third level heading needs to add a supplementary [0-9]) 
	dashlink="$(echo "$line" | sed -r 's|(.+[0-9]+)\.([0-9]+.+\))|\1-\2|')"
	sed -i "s/$line/${dashlink}/" "$files"

	#Puts everything to lowercase after a hashtag
	lowercaselink="$(echo "$dashlink" | sed -r 's|#.+\)|\L&|')"
	sed -i "s/$dashlink/${lowercaselink}/" "$files"

	#Removes spaces (%20) from markdown links after a hashtag
	spacelink="$(echo "$lowercaselink" | sed 's|%20|-|g')"
	sed -i "s/$lowercaselink/${spacelink}/" "$files"

done <<<"$mdlinks2"

      If you are motivated you can still improve your regex If you want :) I’m kinda curious If it’s possible with a one-liner ! Thank again for your help and sorry for the late response !!

    • bizdelnick@lemmy.mlEnglish
      2·
      2 days ago

      I didn’t test this, but it will change the whole URL while changes are only needed in its fragment component (after the first #).