How to remove part of filename and add extension programmatically?

I have hundreds of files in one folder named like this:

index.html?tab=This is - the file 开发者_高级运维name

I would like to remove "index.html?tab=" part and add extension ".txt" to all files. How can I do this using Unix command line tools (I'm using MacOSX 10.6.2)?

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In bash,

for i in index.html\?tab\=*; do mv "$i" "${i:15}.txt"; done

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for file in index.html\?*
do
   mv "$file" "${file#*=}".txt
done