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From: Ralph Corderoy <ralph@inputplus.co.uk>
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Subject: [COFF] Re: Grep has gone overboard
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Hi Michael,

> I was trying to do something very similar using procmail regexes some
> time ago, only with strings instead of individual characters (for
> parsing and matching on arbitrarily-ordered, comma-separated values
> within a header).  I never did come up with a good solution.

Assuming procmail has BRE, this does one interpretation of what you
said.

    $ grep '^ *field *: *\(foo\|bar\|xyzzy\)\( *, *\(foo\|bar\|xyzzy\)\)* *$' <<\E
    > otherfield: foo
    > field:
    > field: ,
    > field:foo
    > field : foo
    > field:xyzzy
    > field: xyzzy,bar, foo , xyzzy
    > field: xyzzy,bar, foo , xyzzy ,
    > E
    field:foo
    field : foo
    field:xyzzy
    field: xyzzy,bar, foo , xyzzy
    $

If I was doing it in sed, I'd s/$/,/ before and s/,$// after so the list
of alternatives need only be given once with each alternative having to
be followed by a comma, i.e. the comma switches from separator to
terminator.

-- 
Cheers, Ralph.