Is it possible to use the open( ) function with piped unix commands?

shaolin has asked for the wisdom of the Perl Monks concerning the following question:

Hi Perl Monks,

Forgive my ignorance as I'm a newbie, but is it possible to do the following in Perl on Unix/Linux?

open(LIST, "| uniq | sort -n");

Where one writes to this filehandle to remove duplicate entries and gets a sorted output?
In the current form the uniq doesn't happen and sort does.
Any tips on getting around this problem would be greatly appreciated.

Thanks again.

Comment on Is it possible to use the open( ) function with piped unix commands? Download Code

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Re: Is it possible to use the open( ) function with piped unix commands? by Joost (Canon) on Jul 18, 2007 at 23:49 UTC
It works just fine from perl. Your problem probably is that uniq only works on sorted lists, i.e. you want `open(LIST, "\| sort -n\| uniq");` [download] and also, you need to explicitly close the LIST handle to make ~~sort~~ the whole pipe stop (update: i don't really know why you need to, but this code doesn't work without the close() statement ): `perl -e'open F,"\|sort\|uniq"; print F "aa\n","bb\n","aa\n","bb\n"; clos +e F'` [download] output: `aa bb` [download] "What should it profit a man, if he should win a flame war, yet lose his cool?"	[reply] [d/l] [select]
Re^2: Is it possible to use the open( ) function with piped unix commands? by runrig (Abbot) on Jul 19, 2007 at 00:01 UTC
And most sort's have a "-u" option so you don't need to use "uniq".	[reply]
Re^2: Is it possible to use the open( ) function with piped unix commands? by ikegami (Patriarch) on Jul 19, 2007 at 14:44 UTC
On `perl`'s side, closing the file handle flushes the data and releases the process (does a `waitpid`). On `sort`'s side, the closed input tells `sort` it's done receiving data so it can proceed to sort and print it.	[reply] [d/l] [select]
Re^3: Is it possible to use the open( ) function with piped unix commands? by Joost (Canon) on Jul 19, 2007 at 15:31 UTC
Yes, but I assumed that perl would close F at end of script, flushing the buffers. ~~Instead, without the close() statement, the program just waits.~~ After some more testing, it appears that I got confused. Perl does close the pipe when you don't do it yourself, but the output is printed just after the new prompt. (which is why i got confused) "What should it profit a man, if he should win a flame war, yet lose his cool?"	[reply]
Re^4: Is it possible to use the open( ) function with piped unix commands? by shaolin (Initiate) on Jul 19, 2007 at 19:43 UTC