لطفا منتظر باشید ...
A.13. Answers to Chapter 14 Exercises
Here''s one way to do it:chdir "/" or die "Can''t chdir to root directory: $!";
exec "ls", "-l" or die "Can''t exec ls: $!";
The first line changes the current working directory to the root
directory, as our particular hard-coded directory. The second line
uses the multiple-argument exec function to send
the result to standard output. We could have used the single-argument
form just as well, but it doesn''t hurt to do it this way.
Here''s one way to do it:open STDOUT, ">ls.out" or die "Can''t write to ls.out: $!";
open STDERR, ">ls.err" or die "Can''t write to ls.err: $!";
chdir "/" or die "Can''t chdir to root directory: $!";
exec "ls", "-l" or die "Can''t exec ls: $!";
The first and second lines reopen STDOUT and
STDERR to a file in the current directory (before
we change directories). Then, after the directory change, the
directory listing command executes, sending the data back to the
files opened in the original directory.
Where would the message from the last die go?
Why, it would go into ls.err, of course, since
that''s where STDERR is going at that point.
The die from chdir would go
there, too. But where would the message go if we can''t re-open
STDERR on the second line? It goes to the old
STDERR. For the three standard filehandles,
STDIN, STDOUT, and
STDERR, if re-opening them fails, the old
filehandle is still open.
Here''s one way to do it:if (`date` =~ /^S/) {
print "go play!\n";
} else {
print "get to work!\n";
}
Well, since both Saturday and Sunday start with an S, and the day of
the week is the first part of the output of the
date command, this is pretty simple. Just check
the output of the date command to see if it starts
with S. There are many harder ways to do this
program, and we''ve seen most of them in our classes.
If we had to use this in a real-world program, though, we''d
probably use the pattern /^(Sat|Sun)/. It''s
a tiny bit less efficient, but that hardly matters; besides,
it''s so much easier for the maintenance programmer to
understand.
