By way of insight (or explanation): the while statement has some magic to do common tasks like this without stating everything specifically.

while (<FOO>) {
   ...
}
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seems to a newcomer like it would mean

while (not_the_end_of_the_file(*FOO)) {
   ...
}
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but in actuality it means

while (defined ($_ = readline(*FOO))) {
   ...
}
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So it does both tasks at once: breaks the loop at the end of the file, AND reads the next line into the default variable $_.