How to correctly pattern match the beginning of the line and replace it with two characters using se-CodePudding

I'm trying to turn the following:

## Features
feature:foo
feature: baz

into:

## Features
- feature:foo
- feature: baz

I came up with this structure:

sed -i '' 's/^[^#]/- /' $1

but that results in:

## Features
- eature:foo
- eature: baz

FWIW my sed command would have worked fine if I was just trying to add it to the beginning of the line without doing any checks for #, but when I do a pattern match, it eats through one of the existing characters.

CodePudding user response：

You may use one of these sed solution:

sed 's/^[^#]/- &/' file
# or
sed '/^#/! s/^/- /' file

## Features
- feature:foo
- feature: baz

To save changes inline on Mac OSX (BSD sed) use:

sed -i '' 's/^[^#]/- &/' file
sed -i '' '/^#/! s/^/- /' file

Note that sed 's/^[^#]/- &/' file uses & in replacement to put matched character back in output string so that that character matched by [^#] is put back in substitution.