xargs: eof ignored (#594)

* Test cases: "perl xargs" and "perl xargs ls"
* Text entered manually:
1
2
3
^D
* xargs correctly runs a program (echo or ls) on 1, 2 and 3, then incorrectly waits to read more data from stdin (end of file was not seen)
* Checking eof() after each read indicates whether xargs should terminate (no more args will follow so the program should not loop)
* Tweak usage string to clarify that "prog" is optional (echo is the default)

Author: mknos

bin/xargs

@@ -31,7 +31,7 @@ my $Program = basename($0);
 my %o;
 getopts('0tn:L:l:s:I:', \%o) or die <<USAGE;
 Usage:
-	$Program [-0t] [-n num] [-L num] [-s size] [-I repl] prog [args]
+	$Program [-0t] [-n num] [-L num] [-s size] [-I repl] [prog [args ...]]
 
 	-0	expect NUL characters as separators instead of spaces
 	-t	trace execution (prints commands to STDERR)
@@ -59,11 +59,12 @@ my @args = ();
 $o{I} ||= '{}' if exists $o{I};
 $o{l} = 1 if $o{I};
 my $sep = $o{'0'} ? '\0+' : '\s+';
-
-while (1) {
+my $eof = 0;
+while (!$eof) {
     my $line = "";
     my $totlines = 0;
     while (<STDIN>) {
+	$eof = eof;
 	chomp;
 	next unless (length && m/\S/);
 	$line .= $_ if $o{I};