my $SomeFile = "delme.txt";

open inFile, "<$SomeFile" or die "Can't open $SomeFile for input: $!";
open outFile, ">~$SomeFile" or die "Can't open ~$SomeFile for output: $!";

print outFile while <inFile>;

close inFile;
close outFile;

unlink "$SomeFile.bak";
rename $SomeFile, "$SomeFile.bak";
rename "~$SomeFile", $SomeFile;