extract string

[Kevin D. Clark]

Ben Scott writes:

>   Is there a tool that quickly and easily extracts one or more columns
> of text (separated by whitespace) from an output stream?  I'm familiar
> with the
>
>           awk '{ print $3 }'
>
> mechanism, but I've always felt that was clumsy.  I've tried to get
> cut(1) to do it in the past, but the field separator semantics appear
> to assume one and only one separator, not "whitespace" (one or more
> space or tab characters).
>
>   I get the feeling there is some command or switch I'm not aware of
> that I should be using.  This hyptherical command might work something
> like this:
>
>          ls -l | foo 3
>
> to extract just the third column (username) from the ls(1) output.

Thoughts:

0:  I've always found awk and cut to be very convenient for these
    operations.  For complex things, I recommend Perl.  In particular,
    awk and Perl allow for pattern separators, as you desire.

1:  You might find awk's -F option to be useful.

2:  Something like this is always fun:

       perl -F: -ane 'print join " ", @F[0,5,6]' /etc/passwd

3:  If you really want foo, how about this:

       foo() {
         if [ $# -eq 0 ] ; then
           foo 0
         else
           awk "{ print `echo "${@}" | sed 's/\([0-9]*\)/\\$\1/g'` }"
         fi
      }

   I leave it to the reader to improve this if so desired.  (-:

Hope this helps,

--kevin
-- 
(There are also also 228 babies named Unique during the 1990s alone,
and 1 each of Uneekm, Uneque, and Uneqqee.)

    -- _Freakonomics_, Steven D. Levitt and Stephen J. Dubner