Sed substitution not doing what I want and think it should do

Question

I have am trying to use sed to get some info that is encoded within the path of a file which is passed as a parameter to my script (Bourne sh, if it matters). From this example path, I'd like the result to be 8

PATH=/foo/bar/baz/1-1.8/sing/song

I first got the regex close by using sed as grep:

echo $PATH | sed -n -e  "/^.*\/1-1\.\([0-9][0-9]*\).*/p"

This properly recognized the string, so I edited it to make a substitution out of it:

echo $PATH | sed -n -e "s/^.*\/1-1\.\([0-9][0-9]*\).*/\1/"

But this doesn't produce any output. I know I'm just not seeing something simple, but would really appreciate any ideas about what I'm doing wrong or about other ways to debug sed regular expressions.

(edit)

In the example path the components other than the numerical one can contain numbers similar to the numeric path component that I listed, but not quite the same. I'm trying to exactly match the component that that is 1-1. and see what some-number is.

It is also possible to have an input string that the regular expression should not match and should product no output.

Answer 1

It looks like you're trying to get the 8 from the 1-1.8 (where 8 is any sequence of numerics), yes? If so, I would just use:

echo /foo/bar/baz/1-1.8/sing/song | sed -e  "s/.*\/1-1\.//" -e "s/[^0-9].*//"

No doubt you could get it working with one sed "instruction" (-e) but sometimes it's easier just to break it down.

The first strips out everything from the start up to and including 1-1., the second strips from the first non-numeric after that to the end.

$ echo /foo/bar/baz/1-1.8/sing/song | sed -e  "s/.*\/1-1\.//" -e "s/[^0-9].*//"
8
$ echo /foo/bar/baz/1-1.752/sing/song | sed -e  "s/.*\/1-1\.//" -e "s/[^0-9].*//"
752

And, as an aside, this is actually how I debug sed regular expressions. I put simple ones in independent instructions (or independent part of a pipeline for other filtering commands) so I can see what each does.

---

Following your edit, this also works:

$ echo /foo/bar/baz/1-1.962/sing/song | sed -e  "s/.*\/1-1\.\([0-9][0-9]*\).*/\1/"
962

As to your comment:

In the example path the components other than the numerical one can contain numbers similar to the numeric path component that I listed, but not quite the same. I'm trying to exactly match the component that that is 1-1. and see what some-number is.

The two-part sed command I gave you should work with numerics anywhere in the string (as long as there's no 1-1. after the one you're interested in). That's because it actually deletes up to the specific 1-1. string and thereafter from the first non-numeric). If you have some examples that don't work as expected, toss them into the question as an update and I'll adjust the answer.

Answer 2

The -n option to sed supresses normal output, and since your second line doesn't have a p command, nothing is output. Get rid of the -n or stick a p back on the end

Answer 3

You can shorten you command by using + (one or more) instead of * (zero or more):

sed -n -e "s/^.*\/1-1\.\([0-9]\+\).*/\1/"

Answer 4

don't use PATH as your variable. It clashes with PATH environment variable

echo $path|sed -e's/.*1-1\.//;s/\/.*//'

Answer 5

You needn't divide your patterns with / (s/a/b/g), but may choose every character, so if you're dealing with paths, # is more useful than /:

echo /foo/1-1.962/sing | sed -e  "s#.*/1-1\.\([0-9]\+\).*#\1#"