The files don't just appear. They grow as the FTP upload progresses. How do you expect to know when the files have finished uploading? Testing for their presense is not sufficient, as shown by my proof below. If you don't take this problem into account, you may end up with only a fragment of the first or second file in the combined file. The two solutions provided to date do not take this problem into account.

Proof:

$ cat a.pl
open(FILE, '> bla') or die("$!");
select FILE;
$|=1;
select STDOUT;
print FILE "test1\n";
print FILE "test2\n";
sleep 10;
print FILE "test3\n";
close FILE;

$ cat a.sh
#!/bin/sh
rm -f bla bla2
perl a.pl &
sleep 5
test -f && cp bla bla2
sleep 10
echo bla:
cat bla
echo bla2:
cat bla2

$ a.sh
bla:
test1
test2
test3
bla2:
test1
test2
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