How to replace all “printLog();” into “//printLog();” but not resulting “////printLog();”?

Question

for example, I want to comment out all printLog() functions in a file:

//printLog();
printLog();
//printLog();

but some printLog() are already comment out, and replacing printLog() with //printLog() directly would result in:

////printLog();
//printLog();
////printLog();

is it possible to replace "printLog();" into "//printLog();" but not "printLog();" originally in "//printLog();"?

Answer 1

You could anchor your search pattern to the beginning of the line:

:%s@^printLog@//&

and maybe take leading white space into account for more safety:

:%s@^\s*printLog@//&

Breaking it down…

• :s allows you to use other characters than forward slashes as separators, that's handy when your search pattern or replacement contain forward slashes. Here I use @ but you can use any character except a-zA-Z0-9\"|. See :help e146.
• The ^ atom represents the beginning of the line so ^printLog will only match printLog if it is at the beginning of a line. See :help /^.
• In the "safe" variant, we add "zero or more white space characters" (\s*) between the beginning of the line and printLog. See :help \s.
• In the replacement part, we reuse the matched text with &. See :help s/\&.