To comment lines 2 through 4 of bla.conf:
sed -i '2,4 s/^/#/' bla.conf
To make the command that you wanted, just put the above into a shell script called comment:
sed -i "$1"' s/^/#/' "$2"
This script is used the same as yours with the exception that the first and last lines are to be separated by a comma rather than a dash. For example:
comment 2,4 bla.conf
An uncomment command can be created analogously.
sed's line selection is quite powerful. In addition to specifying first and last lines by number, it is also possible to specify them by a regex. So, if you want to command all lines from the one containing
foo to the one containing
comment '/foo/,/bar/' bla.conf
BSD (OSX) Systems
With BSD sed, the
-i option needs an argument even if it is just an empty string. Thus, for example, replace the top command above with:
sed -i '' '2,4 s/^/#/' bla.conf
And, replace the command in the script with:
sed -i '' "$1"' s/^/#/' "$2"