How do I use RegExp Replace to replace sentence?

How do I use RegExp Replace to replace below word?

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(1) Replace/Remove what ever word start with "a" and end with "c"!开发者_高级运维

Example (1): abc, xyz, axc, bbb, ccc ayc, a1c, abcc, axxyzc...

Replace after (1): , xyz, , bbb, ccc , , , ...

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(2) Replace/Remove what ever word start with "abc=" and end with "&"!

Example (2): abc=123&xyz=111&abc=xgggf&abc=ffff&abc=xxxx&xyz=kkk&abc=zzz&

Replace after (2): xyz=111&xyz=kkk&

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Thanks~~~

(1):

var replaced = string.replace(/a.*?c/gi, "");

(2):

var replaced = string.replace(/(.*?)xyz=&(.*?)/gi, "$1,$2");

The above is using Javascript. But the general regex's will be the same in all regex flavors.