Re: sed question

[songbird <songbird@anthive.com>]

The Wanderer wrote:
>songbird wrote:
...
>> sed was designed to operate on streams.  a sequence of characters is
>> a stream.  i don't see any reason why putting the variable into the
>> middle of that expression means anything different.
>
> Because sed doesn't see the variable; the variable is handled by the
> shell. sed only sees the result of expanding the variable.
>
> If the variable doesn't contain the delimiting token (the character
> after the initial 's' - in this case, '/'), then things work out fine.
>
> But if the variable does contain that token, then what sed sees contains
> too many instances of that token, and the result is invalid sed syntax -
> so sed errors out, because it doesn't know what to do with what it saw.
>
>
> For example, 's/hello/newstring/' would be a valid sed 's'-expression,
> but 's/a/b/newstring/' would not; the former contains three instances of
> the delimiting token, which is valid, but the former contains four,
> which is not.
>
> If you have the sed expression 's/${oldstring}/newstring/', and you
> define oldstring as having the value 'hello' then sed sees the first
> expression, and you get the good result.
>
> But if you instead define oldstring as having the value 'a/b', then sed
> sees the second expression, and you get a syntax error.
>
>
> (Assuming I'm not mixing things up right now, anyway.)

  :)  thank you for your reply.  now i see it.


  songbird