Re: read from a file and write into the same file

[goibhniu]

I think OP's problems were sufficiently pointed out. I was wondering if lexical file handles (open my $fh vs. open FILE) might be useful. What I found was that I successfully separated the input filehandle pointer from the output filehandle pointer, but the input filehandle stopped at the original eof instead of moving on through the new file contents. Could some wiser monks explain that to me?

C:\chas_sandbox>for %f in (a b c d) Do echo %f>>alpha.txt

C:\chas_sandbox>echo a 1>>alpha.txt

C:\chas_sandbox>echo b 1>>alpha.txt

C:\chas_sandbox>echo c 1>>alpha.txt

C:\chas_sandbox>echo d 1>>alpha.txt

C:\chas_sandbox>perl -le "open my $fh_in, '<', 'alpha.txt'; open my $f
+h_out, '>>
', 'alpha.txt';while (<$fh_in>) {chomp;print $fh_out chr(ord($_)+4); l
+ast if $_
eq 'v'}"

C:\chas_sandbox>type alpha.txt
a
b
c
d
e
f
g
h

[almut]

...but the input filehandle stopped at the original eof

Presumably just the usual Suffering from Buffering. Adding $fh_out->autoflush(1); (after having opened the output file) should make things behave as you expect (fill the file with letters up to 'z').  You also need to load IO::Handle for the autoflush method to be available — i.e. -MIO::Handle if you want to stick with your one-liner :)

BTW, there is nothing special with lexical filehandles in this regard, the piece of code would work just as well with normal filehandles like IN, OUT.