Repeating a regex pattern

Question

First, I don't know if this is actually possible but what I want to do is repeat a regex pattern. The pattern I'm using is:

sed 's/[^-\t]*\t[^-\t]*\t\([^-\t]*\).*/\1/' films.txt

An input of

250.    7.9    Shutter Island (2010)    110,675

Will return:

Shutter Island (2010)

I'm matching all none tabs, (250.) then tab, then all none tabs (7.9) then tab. Next I backrefrence the film title then matching all remaining chars (110,675).

It works fine, but im learning regex and this looks ugly, the regex [^-\t]*\t is repeated just after itself, is there anyway to repeat this like you can a character like a{2,2}?

I've tried ([^-\t]*\t){2,2} (and variations) but I'm guessing that is trying to match [^-\t]*\t\t?

Also if there is any way to make my above code shorter and cleaner any help would be greatly appreciated.

Answer 1

You can repeat things by putting them in parenthesis, like this:

([^-\t]*\t){2,2}

And the full pattern to match the title would be this:

([^-\t]*\t){2,2}([^-\t]+).*

You said you tried it. I'm not sure what is different, but the above worked for me on your sample data.

Answer 2

I think you might be going about this the wrong way. If you're simply wanting to extract the name of the film, and it's release year, then you could try this regex:

(?:\t)[\w ()]+(?:\t)

As seen in place here:

http://regexr.com?2sd3a

Note that it matches a tab character at the beginning and end of the actual desired string, but doesn't include them in the matching group.

Answer 3

why are you doing things the hard way??

$ awk '{$1=$2=$NF=""}1' file
  Shutter Island (2010)

Answer 4

If this is a tab separated file with a regular format I'd use cut instead of sed

cut -d' ' -f3 films.txt

Note there's a single tab between the quotes after the -d which can be typed at the shell prompt by typing ctrl+v first, i.e. ctrl+v ctrl+i

Answer 5

This works for me:

sed 's/\([^\t]*\t\)\{2\}\([^\t]*\).*/\2/' films.txt

If your sed supports -r you can get rid of most of the escaping:

sed -r 's/([^\t]*\t){2}([^\t]*).*/\2/' films.txt

Change the first 2 to select different fields (0-3).

This will also work:

sed 's/[^\t]\+/\n&/3;s/.*\n//;s/\t.*//' films.txt

Change the 3 to select different fields (1-4).