regex match and replace in vscode for repetitive pattern

A generic way to do this is to match and capture the part before the first qualifying / char, match this char without capturing, and then match the part on the right to ensure the context is correct, and then replace with Group 1 value + new char + Group 2 value.

The general scheme is

Find:    (left-hand context)text to remove/replace(right-hand context)
Replace: $1new_text$2

Then repeat until no more changes are made to the document.

In your case, you can use

Find What:   (\sid="[^"/]*)/([^"]*"[^>]*>)
Replace With: $1-$2

See the regex demo. Details:

• ( - Group 1:
  • \s - a whitespace
  • id=" - a fixed text
  • [^"]* - zero or more chars other than a " char
• ) - end of Group 1
• / - a / char
• ( - Group 2:
  • [^"]* - zero or more chars other than "
  • " - a " char
  • [^>]* - zero or more chars other than >
  • > - a > char
• ) - end of Group 2.

This will work for both File search and replace and In-document search and replace feature.

If you are applying the regex against a single document using In-document search and replace feature, you can make use of a lookaround-based pattern to achieve the goal in a single pass:

Find What:   (?<=\sid="[^"]*)/(?=[^"]*"[^>]*>)
Replace With: -

See this regex demo. Details:

• (?<=\sid="[^"]*) - a positive lookbehind that matches a location that is immediately preceded with
  • \s - a whitespace
  • id=" - a fixed text
  • [^"]* - zero or more chars other than a " char
• / - a / char
• (?=[^"]*"[^>]*>) - a positive looahead that matches a location that is immediately followed with
  • [^"]* - zero or more chars other than "
  • " - a " char
  • [^>]* - zero or more chars other than >
  • > - a > char.