One of my program need to execute Unix command from time to time. If I use system(), it would spawn a new process each time, which costs a lot. My solution is to spawn a sh process through open2 or open3, and then simply communicate my Unix command to that sh process.

After the sh process receive my command, it may or may not spawn a new process, depending on the nature of the command, say I can save 50% (the number really depends on what commands I use) cost.

Part of my code read: 
#!/usr/bin/perl

use IPC::Open2;
use strict;

my ($reader, $writer);
my $pid = open2($reader, $writer, "sh") || die "failed";
print $writer "history\n";

while (<$reader>) {
    print "[", $_, "]\n";
}

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Now my problem is that it will not quit the while loop, as there is no eof coming in. So, how can I fix this? ( I also tried open3, the same thing)

By the way, there was a thread leading by help with system function, discussed about why can not call history sh command by using system() call, and no answer came up at that time. My solution actually resolves that problem.

In reply to question for open2, and by the way, resolves an old thread by pg

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