Thank you for your answer. I know this is not the right way to do it. Sorry for this confusion. In fact what I was trying to do is to compare each line of file1 with each line of file2, not just match each other. I had two ways to do it,first,open and close file2 for each line for file1, thus I can iterate all the lines of file2 every time. Second, I can build an array to store items of file1 or file2,then iterate them. Using hash should be fine too. But either way (opening/closing file or array/hash) has its own shortcoming. opening/closing file will be slower (right?),array/hash will consume memory. These two files are very very huge files. I recalled that I might read it somewhere that we could reset the position of <> operator, and every time when one round iteration is done, it might be set back to do another round iteration. I am not sure if this method exists. But if there is one like this, I could be able to re-iterate the file without opening/closing files or building arrays/hashes. Thanks.

In reply to Re^2: how to reset the input operater in while loop? by lightoverhead
in thread how to reset the input operater in while loop? by lightoverhead

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