Bash script to replace matched substrings within larger substring - string

Question

I'm trying to write a bash script to replace the newline characters and *s from comments, but only if that comment contains a particular substring.
// file.txt
/**
* Here is a multiline
* comment that contains substring
* rest of it
*/
/**
* Here is a multiline
* comment that does not contain subNOTstring
* rest of it
*/
I would like the final result to be:
// file.txt
/** Here is a multiline comment that contains substring rest of it */
/**
* Here is a multiline
* comment that does not contain subNOTstring
* rest of it
*/
I have a regex that matches multiline comments: \/\*([^*]|[\r\n]|(\*+([^*\/]|[\r\n])))*\*\/ but can't figure out the second part, of only matching with the substring, and then replacing all the /n * with just
So to make sure my question is articulated correctly
Make a match of a substring within a file. i.e. comment
Make sure that match includes substring.
Replace all substring within the first match with another string. i.e. n/ * with

Answer 1

If python is your option, would you please try:
#!/usr/bin/python
import re # use regex module
with open('file.txt') as f: # open "file.txt" to read
str = f.read() # assign "str" to the lines of the file
for i in re.split(r'(/\*.*?\*/)', str, flags=re.DOTALL): # split the file on the comment including the comment in the result
if re.match(r'/\*.*substring', i, flags=re.DOTALL): # if the comment includes the keyword "substring"
i = re.sub(r'\n \* |\n (?=\*/)', ' ', i) # then replace the newline and the asterisk with a whitespace
print(i, end='') # print the element without adding newline
re.split(r'(/\*.*?\*/)', str, flags=re.DOTALL) splits "str" on the comment
including the comment in the splitted list.
The flags=re.DOTALL option makes a dot match with newline characters.
for i in .. syntax loops over the list assiging "i" to each element.
re.match(r'/\*.*substring', i, flags=re.DOTALL) matches the element
which is a comment including the keyword "substring".
re.sub(r'\n \* |\n (?=\*/)', ' ', i) replaces a newline followed by
the " * " in the next line with a whitespace.
\n (?=\*/) is a positive lookahead which matches a newline followed
by " */". It will match the last line of the comment block leaving the
"*/" as is.
[Edit]
If you want to embed the python script in bash, would you please try:
#!/bin/bash
infile="file.txt" # modify according to your actual filename
tmpfile=$(mktemp /tmp/temp.XXXXXX) # temporary file to output
# start of python script
python3 -c "
import re, sys
filename = sys.argv[1]
with open(filename) as f:
str = f.read()
for i in re.split(r'(/\*.*?\*/)', str, flags=re.DOTALL):
if re.match(r'/\*.*substring', i, flags=re.DOTALL):
i = re.sub(r'\n \* |\n (?=\*/)', ' ', i)
print(i, end='')
" "$infile" > "$tmpfile"
# end of python script
mv -f -- "$infile" "$infile".bak # backup the original file
mv -f -- "$tmpfile" "$infile" # replace the input file with the output