On Wednesday 04 Aug 2010 09:06:16 Linda Walsh wrote:
> On 8/1/2010 8:11 PM, Chris F.A. Johnson wrote:
> > On Sun, 1 Aug 2010, Linda Walsh wrote:
> >> I have:
> >>
> >> w="/home/law/bin/package: line 5: type: xx: not found"
> >>
> >> The =~ operator is suppose to use the RH Expr as a ext.-regex.
> >>
> >> So why doesn't this match and print "not found"?
> >>
> >> if [[ $w =~ ".*not found.*" ]]; then echo "not found"; fi
> >>
> >> It prints nothing. Seems like such a basic concept. Sorry, this
> >> newbie needs help on such trivial matters. :-(
> >>
> > When quoted, the right-hand argument is matched as a string, not an
> > expression.
>
> So that's how it is...
>
> Aren't single quotes reserved for making things literal, while
> double quotes are used for grouping, yet interpreting what is between them
> (expansions and such).
>
> Is there a reason "RH =~" was made inconsistent regarding this practice?
>
> I might note: the man page makes no reference to such heinous behavior,
> leading one me to think I'd use single quotes if I didn't want the
> contents to be 'active' Though to tell the truth. Technically, it says:
>
> An additional binary operator, =~, is available, with the same
> precedence as == and !=. When it is used, the string to the
> right of the operator is considered an extended regular expres-
> sion and matched accordingly (as in regex(3)).
>
> I don't see anything about quotes making the =~ operator behave like
> the == operator. I'm not sure I see the usefulness in that.
> If there is, then is it necessary to reserving both single and double
> quotes to make "=~" behave like "=="?
From the Changelog:
This document details the changes between this version, bash-3.2-alpha,
and the previous version, bash-3.1-release.
...
3. New Features in Bash
...
f. Quoting the string argument to the [[ command's =~ operator now forces
string matching, as with the other pattern-matching operators.
From the file COMPAT:
33. Bash-3.2 adopts the convention used by other string and pattern matching
operators for the `[[' compound command, and matches any quoted portion
of the right-hand-side argument to the =~ operator as a string rather
than a regular expression.
34. Bash-4.0 allows the behavior in the previous item to be modified using
the notion of a shell `compatibility level'.
Finally, to set a given compatibility level, one uses
shopt -s compat31
This is in the man page:
compat31
If set, bash changes its behavior to that of version 3.1 with respect
to quoted arguments to the conditional command's =~ operator.
So your example would have worked with "shopt -s compat31".
--
D.
