Re: sed syntex in procmailrc question

On Fri, Oct 14, 2011 at 5:46 AM, Harry Putnam <[email protected]> wrote:
> Zhiliang <[email protected]> writes:
>
>> I have a recipe wish 'sed' in one of my Smartlist rc, like:
>>
>>    sed 's/SUBJET/'"$SUBJ"/g
>>
>> which works fine.  I forgot where did I copied it from but have been
>> puzzled by its syntex with respect to the use of the single quotes
>> "'".
>
> I'm certainly not any kind of expert on sed but I think what you may
> be seeing is really a shell expansion thing.

To expand just a little on Harry's correct explanation:

In the literal example you included, the single quotes around
's/SUBJET/' are unnecessary.  You only need quotes to protect spaces,
dollar signs, and globbing characters like *?[].

However, my guess is that your real sed expression, which you have not
shown us, doesn't have the string SUBJET but instead has a complex
string that might contain some of those special characters that need
quoting.

In that case for clarity I might have written such an expression as

sed -e s/'The Real String Goes Here'/"$SUBJ"/g

rather than butting the two sets of quotes up against each other.