First of all, I'd recommend to avoid the use of -i as it will replace the files in-place without confirmation.

This is a working version of what you were trying to accomplish and outputs to the standard output (the terminal):

sed 's#^//[ 	]test$#test#g' file.conf

aaa

bbb

ccc

test

ddd

test

Optionally pipe it through less by appending | less to be able to paginate through large amounts of output.

The above is all very specific to the sequence of test, so to more generalize, you can try this:

sed 's#^//s(.*)$#1#g' file.conf

It will remove the // part and any whitespace until the actual text, whatever this text is.

If you like the result, you can add the -i flag again to replace the file.

To tell more about your attempt and explain why my example does work:

sed -i `s#^//[ 	]test#test#g'

• You are using a backtick (`) which is interpreted by your shell rather than Sed. A simple single quote (') should have been used here probably.


• The hashes (#) are your chosen delimiter, a good alternative to the common forward slash (/) as your match is about this same character and this avoids the need for escaping.



• The pattern in the command s/regexp/replacement/ is a standard one as mentioned in the manpage, among many others: man 1 sed:

  
  
  

  
  

  s/regexp/replacement/

  
  
  

  Attempt to match regexp against the pattern
  space. If successful, replace that portion matched with replacement.
  The replacement may contain the special character & to refer to that
  portion of the pattern space which matched, and the special escapes
  1 through 9 to refer to the corresponding matching
  sub-expressions in the regexp.

  
  



• rexexp in the above is a commonly used abbreviation for regular expressions.


• The regular expression ^//[ ]test$ matches lines starting (^) with two forward slashes, followed by a space or a tab character, followed by the exact sequence test and a line ending ($).


• The g flag is to do this operation in a global way as explained here.


• An input file is missing and should be given after the Sed-command.