On Fri, Oct 14, 2011 at 5:46 AM, Harry Putnam <reader(_at_)newsguy(_dot_)com>
wrote:
Zhiliang <hu(_at_)animalgenome(_dot_)org> 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.
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