sed with special characters

Question

I have this line that I want to use sed on:

--> ASD = $start ( *.cpp ) <--

where $start is not a varaiable, I want to use sed on it a

Answer 1

The chacters $,*,. are special for regular expressions, so they need to be escaped to be taken literally.

sed 's/ASD = \$start ( \*\.cpp )/ASD = \$dsadad ( .cpp )/' somefile

Answer 2

Backslash works fine. echo '*.cpp' | sed 's/\*//' => .cpp

If you're in a shell, you might need to double escape $, since it's a special character both for the shell (variable expansion) and for sed (end of line)

echo '$.cpp' | sed "s/\\$//" or echo '$.cpp' | sed 's/\$//' => '.cpp'

Do not escape ( or ); that will actually make them them special (groups) in sed. Some other common characters include [ ] \ . ?

This is how to escape your example:

sed 's/ASD = \$start ( \*\.cpp )/ASD = $dsadad ( .cpp )/' somefile

Answer 3

sed 's/\$start/\$dsadad/g' your_file
>> ASD = $dsadad ( *.cpp ) 

sed 's/\*//g' your_file
>> ASD = $start ( .cpp ) 

To follow your edit :

sed -i 's/ASD = \$start ( \*.cpp )/ASD = \$dsadad ( .cpp )/' somefile
>> ASD = $dsadad ( .cpp )

Add the -i (--inplace) to edit the input file.