Re: Help a sed noob

[Jeff King <peff@peff.net>]

On Sat, Aug 04, 2007 at 02:18:11PM +0200, martin f krafft wrote:

> The behaviour is absolutely unclear from the manpage and defies my
> logic. Can you elaborate a bit, even though this is off-topic?

The original sed code in question was:

                sed -ne '/^URL: */{
                        s///p
                        q
                }' "$GIT_DIR/remotes/$1"

There are a few things to note:
  1. -n means "do not print lines by default"
  2. sed addresses consist of an address (in this case a regex meaning
     "do this for lines that match the regex") and a command
  3. The braces start a set of commands, so that for lines matching the
     address, we do all of the commands.
  4. An empty matching portion for a regex means "use the last regex".

So this script comes down to:
  - don't write any lines except the ones we match
  - find a line that starts with URL:
    - replace the URL: part with nothing
    - print the result
    - quit

It could be more simply written as:

sed -ne 's/^URL: *//pq'

which uses the substitution as an address, but I don't know whether that
was allowed in the original sed.

-Peff