synx | line tool that reorganizes your Xcode project folder | Plugin library

The syntax is s/ what to replace / what to replace it with /. You are missing the second part. Even if you want to replace it with nothing, you need all three slashes; just don't put anything between the last two. As it is, you have only one slash, because the second one is quoted with \, meaning sed will treat it as part of the expression and look for a literal / in the input.

The beginning of your regex is also wrong. \[0-9]{2} matches the literal string [0-9 followed by exactly two right brackets (]]). Remove the initial backslash (\) if you want to match "exactly two digits".

Also, you never need to do cat filename |; you can just do < filename. In this specific case, sed takes a filename parameter, so you can do without the <, too.

So it should be something like this;