what is ^M at the end of a line?

[email protected] ("Remy Guo")
Newsgroups perl.beginners
Message-ID <[email protected]> 
hi all,
i have a text processing script that can work with a file but cannot work
with another file that has the same content.
as i compared the 2 files, i found the file that cannot work has a "^M" at
the end of each line. what is this? is this what made it not work?
by the way, i'm under unix.
thanks....

-Remy
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