Re: Using $ in quotes with characters after it

[Mike Frysinger]

On Saturday 24 March 2012 15:06:00 Dan wrote:
> This is the output after running `set -x`.  It looks like the shell is
> behaving properly.  It's un-escaping the question mark when it's supposed
> to be and it isn't when it isn't supposed to be.  Grep shouldn't be
> producing that output though.  The only explanation I can think of is that
> the wildcard is being too greedy and consuming all of the string.  But from
> what I know that's not how it works.

seems correct to me.  in the first two, grep gets a question mark with a 
backslash.  in the last one, it doesn't because the shell processed it first.  
if you read the man page, it says that in a basic regular expression (which 
you're doing because you didn't use -E or run egrep), a plain "?" has no 
meaning -- it's just another character.  grep needs to see the backslash to 
treat it specially.  further, the anchor characters ("$" and "^") only have 
meaning if they are in the last or first position respectively.  otherwise, 
they're just another character to match.

hence, this command:
        grep '^abc.*$\?' testfile
means "anchor to the start of the line, then match abc, then match anything, 
then either anchor to the end of the line or don't".  so really, "$\?" at the 
end of the regexp is completely pointless.

but this command:
        grep ^abc.*$\? testfile
means "anchor to the start of the line, then match abc, then match anything, 
then match a dollar sign, then match a question mark".
-mike

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