On Wed, Feb 06, 2002 at 03:05:29PM +0100, Jorge Goncalvez wrote:
> I tried this:
> @Symlink=("$program_path\\install.lnk",
> "$program_path\\linux.ram.lnk",
> "$program_path\\alize\\install.lnk",
> "$program_path\\alize\\startup.txt.lnk");
>
> foreach (@Symlink)
> {
> if (-e $_)
> {
>
> system "rm $_";
>
> }
> }
>
> but it seems not to work?Why?
Looking at the '\\' in your filenames suggests that you're running
Windows? The 'rm' program is a Unix program and although there are
versions for Windows too - using Cygwin e.g. - you most probably just
don't have 'rm'.
Look here:
---------- snip ----------
kanku-dai:~$ perldoc -f unlink
unlink LIST
unlink Deletes a list of files. Returns the number of
files successfully deleted.
...
If LIST is omitted, uses $_.
---------- snip ----------
The perl builtin 'unlink' does what 'rm' does, but from within perl, so
you don't need to rely on "external" software.
Handily, it accepts lists, so given your above example you can remove
your 'foreach' with
unlink @Symlink;
BUT WARNING: The checks are still missing.
That's no real problem since 'unlink' simply ignores the missing files,
but here's how you could do them anyways:
a.)
unlink grep { -e $_ } @Symlink;
b.)
-e $_ && unlink foreach (@Symlink);
Check the documentation for grep (perldoc -f grep) to learn more about
that. Basically grep gets a piece of code and a list. It runs the code
for each element in the list and returns as result a new list that
contains all elements that let the passed code return a 'true' value.
You could do the same like this:
my @newlist;
foreach (@Symlink) {
if (-e $_) {
push @newlist, $_
}
}
unlink @newlist;
b. looks a bit more cryptic but I think still explainable: We use 2
programming idioms here: shortcut evaluation and modifiers.
First, lets talk about the modifiers:
---------- snip from 'perldoc perlsyn' ----------
Simple statements
...
Any simple statement may optionally be followed by a SIN-
GLE modifier, just before the terminating semicolon (or
block ending). The possible modifiers are:
if EXPR
unless EXPR
while EXPR
until EXPR
foreach EXPR
---------- snip ----------
What this short sentence implies is that you can add a clause to any
simple expression.
if (-e $my_file) {
unlink $my_file;
}
is equivalent to
unlink $my_file
if -e $my_file;
Same goes for the 'foreach' loop:
foreach (@Symlink) {
unlink
}
could also be written
unlink
foreach @Symlink;
Above statement already does the job, but we wanted to include the test
for existence of the file, which brings us to shortcuts:
Shortcut evaluation is the simple concept of bailing out of the
condition as soon as it cannot any longer be true.
A '&&' test is only true if both sides of it are true. So if the left
side of the '&&' fails there's no need to look at the right side, so the
whole expression fails immediately.
Since functions like 'unlink' return a value, we can use them as part of
that '&&' statement, which brings us back to our example:
-e $_ && unlink
If the file doesn't exist, perl skips the left half of the '&&' so the
'unlink' is never called for non-existant files.
Now we have a working expression that we can round up with our
'modifier' foreach
-e $_ && unlink
foreach (@Symlink)
Voila.
--
If we fail, we will lose the war.
Michael Lamertz | [EMAIL PROTECTED]
Nordstr. 49 | http://www.lamertz.net - http://www.perl-ronin.de
50733 Cologne | Priv: +49 221 445420
Germany | Mobile: +49 171 6900 310
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