Re: NON-trivial regular expression problem (could not find on google)

[AW <adouble_uu@hotmail.com>]

Instant Democracy wrote:
> Regular expression facilities are slightly varied in
> sed
> awk
> lisp
> emacs-lisp
> Therefore these newsgroups can all contribute to the discussion.
> 
> A frequent problem involves simplifying a pathname. The string format we
> can expect to encounter is covered by the following three examples:
> 
> "dir.name/../dir/../file"
> "dir/../d2/../file.ext"
> "d1/d2/../../file.ext"
> 
> The "" are part of the string, and not just string delimiters. These
> strings are inside regular text on the line. The paths are never
> absolute so that you will not encounter "/d1/file.ext".
> 
> The task is to eliminate patterns such as 
>     DIRNAME/../
> from the path because they are redundant.
> 
> For lines which do not have ../.. in them, this is
> trivial, for example by regexp in sed, emacs etc.
> 
> The real problem is constructing a regular expression for
> the DIRNAME before the /..
> 
> This DIRNAME can be described as a string that contains neither
> / not double-dot but anything else. Perhaps I am overlooking
> something else about DIRNAME.
> 
> The regular expression for the first two cases is demonstrated by this
> sed script although the lisp variants are identical.
> 
> sed 's,\(^.*\)\(/\|"\)\([^/][^/]*/\.\./\)\(.*"\),\1\2\4,'
> 
> The regex I use for DIRNAME is [^/]+ written above using * because
> sed is without plus.
> 
> I will follow all the cross-posted newsgroups. If you prefer, because
> some people are allergic to any cross-posting, you can post your reply
> in just one of the groups pertaining to your application, ie lisp/elisp/sed/awk.
> 
> democrat
> 

Using the shell is easier, but here goes.

BEGIN { FS="/"} { for( i=2;i<=NF;i++) { if( $i == "." ) $i =""; if($i == 
"..")  $(i-1) == ""; print; }

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