Prepend ## to every line in a text file
Solution 1:
You can use sed to do that:
sed -i.bak 's/^/##/' file
This replaces the start of the line (^) with ##.
With the -i.bak switch, sed edits the file in-place, but creates a backup copy with extension.bak.
Solution 2:
Here is a solution to this problem using perl
perl -e 'while (<>) {print "##$_"}' < infile > outfile