Re: bash, grep, and regular expressions

From: Freddy Freeloader (fredddy_at_cableone.net)
Date: 02/18/05

  • Next message: Todd A. Jacobs: "Re: bash, grep, and regular expressions" 
    Date: Fri, 18 Feb 2005 09:56:29 -0800
To: debian-user@lists.debian.org

    Peter Simpson wrote:
    > On Friday 18 Feb 2005 16:38, Freddy Freeloader wrote:
    >
    >>Matt Zagrabelny wrote:
    >>
    >>>>I have ls aliased to ls -al. What I've been attempting to do with grep
    >>>>and regular expressions is list only non-hidden directories and/or
    >>>>files. I am unable to come up with an expression that will elimate
    >>>>hidden files and return non-hidden files at the same time.
    >>>
    >>>the last sentence above is a little misleading. ls does that by default.
    >>>
    >>>so examples of what you want are:
    >>>
    >>>.bashrc
    >>>something.cc
    >>>bin/
    >>>
    >>>examples of what you dont want are:
    >>>
    >>>.ssh/
    >>>.gnome2/
    >>>
    >>>is this correct?
    >>>
    >>>-matt zagrabelny
    >>
    >>What I'm trying to do is return something like this
    >>
    >>test.txt
    >>bin/
    >>
    >>rather than
    >>
    >>.ssh/
    >>test.txt
    >>bin/
    >>.bashrc
    >>
    >>I have found some regular expressions that will filter out specific
    >>files and extensions, but not something that will filter exclusively on
    >>the . that signfies a hidden file or directory. The best luck I've had
    >>in filtering is to do something like this:
    >>
    >>ls -al | grep -e ^d | grep -e '[.][a-z]'
    >>
    >>This will filter to return directories only with the first grep command
    >>and then the second grep will return only hidden directories that begin
    >>with small caps. However, where I run into problems is:
    >>
    >>ls -al | grep -e ^d | grep -e '[^.][a-z]'
    >>
    >>You would think this would return only directories that begin with
    >>anything except . and begin with lower case letters. This however is not
    >>true. It returns all directories and ignores case altogether.
    >
    >
    > Your search matches any string in the line that contains something that is not
    > a period, followed by a lower case letter.
    >
    > This matches pretty much anything.
    >
    > What you want to do is limit this somewhat!
    >
    > A better idea would be to match two numbers followed by a space, followed by
    > your letter.
    >
    > What works for me is:
    >
    > ls -al | grep -e ^d | grep -e ':[0-9][0-9] [^\.][a-zA-Z]'
    >
    > HTH.
    >
    >

    Your expression returns an empty set.

    You were correct in saying that my second expression was not selective
    enough. I had left a portion of it out.

    ls -al | grep -e ^d | grep -e '\<[^.][a-z]'

    This also returns all directories. It doesn't matter whether they are
    hidden or not. The \< should limit the expression to searching for the
    beginning of a word that starts with anything except a ".". However, it
    does not do that. It returns exactly the same thing as the other less
    selective statement. When I remove the ^ from [^.] it returns an empty
    set.

    It's as if grep doesn't recognize the space between the time column and
    the file name column as a separator between words, but as just another
    character in a word. 

    -- 
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