Argthtjtr

I need to delete some kind of characteristic, single line C++ comments from all files in our repository. Code looks something like this:

some_code

// characteristic_comment_to_delete

some_more_code // another_comment

another_line_with_code // characteristic_comment_to_delete

even_more_code

As a result, I would like to get this:

some_code

some_more_code // another_comment

another_line_with_code

even_more_code

I used sed command that makes my result almost as good as I would like:

#sed -i -e 's&// characteristic_comment_to_delete.*&&g' some_file.cpp

some_code



some_more_code // another_comment

another_line_with_code

even_more_code

Unfortunately, leaving those blank lines is unacceptable solution, so I need somehow improve my command so that it removes whole line, but only if it is left blank after removing this specific comment.

Sed has a d command for deleting whole lines - it can also take an arbitrary (non /) delimiter, however it needs to be escaped with on first use. So you could do something like

$ sed -e '#^// characteristic_comment_to_delete$#d' -e 's#// characteristic_comment_to_delete.*##' file

some_code

some_more_code // another_comment

another_line_with_code 

even_more_code

to first delete lines that consist entirely of // characteristic_comment_to_delete, then substitute any remaining occurrences.

(I changed your & to # to avoid confusion with the sed & replacement operator).

With GNU sed:

sed 's|s*// characteristic_comment_to_delete.*||;T;/./!d'

T is a GNU extension that branches off unless the previous s substitution was successful. So if no comment was removed, we branch off, and the next /./!d (which deletes the line unless it contains at least one character) is skipped.

Standard equivalent:

sed '/[[:space:]]*// characteristic_comment_to_delete.*/{s///;/./!d;}'

Or:

sed 's|[[:space:]]*// characteristic_comment_to_delete.*||

     t 1

     b

     :1

     /./!d'

Both suppress empty lines only if the substitution was successful.

If you accept an AWK solution:

awk -F "[   ]*//[   ]*characteristic_comment_to_delete.*" '$1 != "" { print $1; }' some_file.cpp

Note: The pattern contains a space and a TAB between the brackets [ ].

This solution does not correctly handle string literals containing the comment pattern, e.g.
char text = "// characteristic_comment_to_delete bla bla";

Demonstrating storing the comment in a shell variable, and escaping the slash characters with shell parameter expansion. Otherwise, same as steeldriver's answer.

$ comment='// characteristic_comment_to_delete'

$ sed -e "/^[[:blank:]]*${comment////\/}/d" -e "s/${comment////\/}.*//" file

some_code

some_more_code // another_comment

another_line_with_code 

even_more_code