Re: [SLUG] grep question

["Amos Shapira" <amos.shapira@xxxxxxxxx>]

On Sun, Apr 13, 2008 at 10:02 PM, Alex Samad <alex@xxxxxxxxxxxx> wrote:
> On Sun, Apr 13, 2008 at 09:55:13PM +1000, Amos Shapira wrote:
>  > On Sun, Apr 13, 2008 at 9:41 AM, Alex Samad <alex@xxxxxxxxxxxx> wrote:
>  > >  > Try grep -Ev '^(\W*;|$)'
>  > >  great that works, (i changed to \s* instead, also tried the [[:space:]]
>  > >  and it worked)
>  > >
>  > >  I don't understand hwy i need to test for ^$, I had thought that once a
>  > >  line test positive for ^\s*; it would be excluded ?
>  >
>  > Because empty lines do not match the '^\W*;' part (they don't have a
>  > ';' in them to match the regular expression) and so grep prints them.
>  > The '^$' part matches empty lines and so they are filtered out.
>
>  but the line has already been matched why is it not discarded ?

Nope. The empty lines you see in the output (without the "^$" match)
are empty lines from the original file (look them up), not lines which
matched the ":" RE.

When you look for empty lines in the input, be aware that there could
be lines containing only white space, which won't match "^$" (to test,
use "cat -e" on the file) but still look empty to "the naked eye",
maybe you want you change that RE to something like:
"^[:space:]*(;|$)" (i.e. match lines which begin with ";" (optionally
preceded by white space) or which contain only zero or more white
spaces).

--Amos