Is there a single regular expression to replace a number in a delimited list?

I have a string that can range from the empty string to an arbitrary list of comma delimited numbers. For example: "1,2,3"

Unfortunately as I wr开发者_开发技巧ite the code to remove an element I have a bunch of if statements--mainly to deal if it is the first, last, or only element in the list. I keep thinking there has got to be a better way!

For example, I would need to be able to remove the element '2' in the following lists:

"1,2,3"
"1,3,2"
"2,1,3"
"2"
"12,2,21"
""

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This should do what you want:

/(\b|,)2(\b|,)/

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Removing (see below for replacing)

I couldn't find a simple single expression to remove, so it seems the best thing is just to match each of the patterns in sequence:

echo "x,x,1,x,2,x,x" | sed -e 's/,x,/,/g;  s/^x,//;  s/,x$//;  s/^x$//'

A little verbose, but very readable.

Replacing

echo "x,x,1,x,2,x,x" | sed -e 's/,x,/,y,/g;  s/^x,/y,/;  s/,x$/,y/;  s/^x$/y/'