[Cialug] Regular Expression for Pathnames

[jim kraai]

there needs to be a regex intro/refresher class every few years

On Mon, Nov 24, 2014 at 10:49 PM, Todd Walton <tdwalton at gmail.com> wrote:

> Fabulous! I knew there was answer. Thanks, guys!
>
> --
> Todd
>
>
> On Mon, Nov 24, 2014 at 1:43 PM, Daniel A. Ramaley <
> daniel.ramaley at drake.edu
> > wrote:
>
> > I realized right after sending it that the way your problem is stated,
> > you might want to match different numbers of slashes. To match strings
> > that have between 1 and 3 (inclusive) slashes, change the part between
> > curly braces to be "1,3" instead of just "3":
> >
> >         egrep '^(/[^/]+){1,3}$'
> >
> > Explaining what this bit of line noise means:
> >
> > ^       Match beginning of line.
> > ()      Groups stuff and treats it as one object.
> > /       Match a literal "/".
> > []      Matches a single character provided inside the brackets.
> >         For example, "[abcde]" will match 5 lowercase letters.
> > ^       If used as the first character in square brackets, this
> >         inverts the characters matched.
> > /       Match "/". Note that it is inverted due to the preceding
> >         "^" and so therefore means match anything *except* "/".
> > +       Match the [] expression 1 or more times.
> > {}      Counter. How many times we should match.
> > 1,3     Match between 1 and 3 times, inclusive.
> > $       Match end of line.
> >
> > You can find more precise explanation in regex documentation; this is
> > just off the top of my head. The most important thing with reading
> > regexes is figuring out how they are grouped. The basic pattern here is
> > the (foo){bar} which just means "match foo, bar number of times".
> >
> > On 2014-11-24 at 10:58:24 Ron Houk wrote:
> > > Wow. Your solution is a lot more elegant. I'm still trying to learn
> > > this stuff. :)
> > >
> > > On Nov 24, 2014 10:35 AM, "Daniel A. Ramaley"
> > > <daniel.ramaley at drake.edu>
> > > wrote:
> > > > This should work for your purposes if all the data looks like the
> > > > samples. Set the number between curly braces to whatever you need.
> > > > (Note that your sample data didn't have any matches for just 2
> > > > slashes, but does for 3 slashes.)
> > > >
> > > >         egrep '^(/[^/]+){3}$'
> > > >
> > > > On 2014-11-24 at 10:23:07 Todd Walton wrote:
> > > > > If I have a text file full of pathnames, like:
> > > > >
> > > > > /var/log/folder1
> > > > > /var/log/folder2
> > > > > /home/todd/mydir
> > > > > /var/log/folder1/fileh
> > > > > /var/log/folder1/foldersub/fileh
> > > > >
> > > > > ...etc, what's the regular expression to find where a string has
> > > > > exactly two (or however many) forward slashes to the left of it?
> > > > > I
> > > > > have a 360,000 line list of path names, and I'd like to find where
> > > > > a
> > > > > certain string falls early in the path.  I'm really only
> > > > > interested
> > > > > in paths where it's in the top three or four directories.
> > > > >
> > > > > --
> > > > > Todd
> > > > > _______________________________________________
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> > > >
> > > > __
> > > > Daniel A. Ramaley  |  Network Engineer 2
> > > > Drake Technology Services (DTS) | Drake University
> > > >
> > > > T: +1 515 271-4540
> > > > F: +1 515 271-1938
> > > > E: daniel.ramaley at drake.edu
> > > >
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> > __
> > Daniel A. Ramaley  |  Network Engineer 2
> > Drake Technology Services (DTS) | Drake University
> >
> > T: +1 515 271-4540
> > F: +1 515 271-1938
> > E: daniel.ramaley at drake.edu
> >
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