Contributed by Anonymous Monk on Jun 30, 2000 at 18:05 UTC
Q&A  > input and output


I have a loop which processes a very large list of items. For each item it processes, it prints a dot to stdout (the console). However, instead of watching my "line of dots" growing until the last item is done, all of the items get processed and then I see all the dots appearing at once. Is there an equivalent to C's flush() function for Perl ?

Answer: How to flush output to the console?
contributed by QandAEditors

Autoflush the buffer. This is directly from perlvar:

If set to nonzero, forces a flush right away and after every write or print on the currently selected output channel. Default is 0 (regardless of whether the channel is actually buffered by the system or not; $| tells you only whether you've asked Perl explicitly to flush after each write). Note that STDOUT will typically be line buffered if output is to the terminal and block buffered otherwise. Setting this variable is useful primarily when you are outputting to a pipe, such as when you are running a Perl script under rsh and want to see the output as it's happening. This has no effect on input buffering. (Mnemonic: when you want your pipes to be piping hot.)
So, try $|++ or $| = 1. Both will turn on autoflushing, but I tend to like $| = 1 better since it is less cryptic for novices.

Answer: How to flush output to the console?
contributed by Anonymous Monk

Turn on autoflush in a BEGIN block:

BEGIN { $| = 1 }
Answer: How to flush output to the console?
contributed by QandAEditors

Turn on "autoflush":

Put this just after your #!/.../perl line.

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