Search Results

GNU sed and maybe BSD sed support ExtendedRE with a - r or -E option.
Then you can do a universal search:
sed -i -r '/(^|,)GETaboutUsCSS(,|$)/d' file
At the left side there must be either the...

Have a ^ anchor for the beginning of the line, and a $ anchor for the end of the line:
sed -i '/^GETaboutUsCSS$/d' file