My last post show what I have tried before I post my question.

And the pseudo code show exactly the problem:
1°) There is one parameter ($1) for the file name : "/root/Documents/file_text.txt" in the example
2°) There is one parameter ($2) for the first token : "In the Linux startup process" in the example
So we can ignore the begin of the text file
3°) There is one parameter ($3) for the second token : "Like init"
So we can search safely from this second token because we are protected by the first token and because we know that the second token appear only once after the first token. So we can ignore all the text until this second token after having found the first token.
4°) There is one parameter ($5) for the last token : "ways" in the example
So we stop searching beyond this token.
As I have no idea how to pass the character " \ " or " } " or " ' " or " . " as token, I have make my test with a single word.
5°) There is one parameter ($4) for the token to search for : "manage" in the example.
This token could start at the very beginning of a line, after a blank or after a tab ( some thing like [ ^ | \t | ]).
As I don't know how to represent this ORed expression, I give my example with a simple word.

As you can see, my pseudo code is unchanged.

What I would like is :
1°) make simpler

Code:

my_function () {
CMD="COUNT=\$(sed -n '/^$1/,\$p'  $2 | sed -n '/^$3/,\$p' | sed '/$5/ q'  | sed -n '1p' | grep -c '$4'   )"
eval $CMD
if [[ $COUNT -gt 0 ]] ; then
    return 0
else
    return 1
fi
}

2°) how to pass a \, a }, a ' as $5
3°) how to pass [^ | \t | space ]token_to_pass as $4