Re: More on directory recursion

I don't know much about this, but there is apparently a security issue here, so I'd like to extend this question a bit. On page 321 of the Perl Cookbook, it states

Perl's built-in glob and <WILDCARD> notation ... currently use an external program to get the list of filenames on most systems. (English purists like myself will cringe at the placement of the last prepositional phrase, but that's another issue :).

The Holy Cookbook further states that

The use of the shell on Unix also makes this inappropriate for setuid scripts. While I have seen warnings about setuid and setgid scripts, I haven't had the opportunity to write any yet, so I am not aware of the security issues here. Enlightenment would put me a step closer to Perl nerdvana :)

Comment on Re: More on directory recursion

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RE: Re: More on directory recursion by takshaka (Friar) on Jun 12, 2000 at 22:51 UTC
Pre-5.6 glob forks a shell and lets csh do the filename expansion. Allowing users to pass arbitrary strings to the shell is a Bad Thing, especially when you're running as root. 5.6, however, implements glob internally through File::Glob, so it's a lot safer (though that feature is currently labelled "experimental"). Update: This snippet from perlop should make it clear what is going on with glob on pre-5.6 Perl: `while (<.c>) { chmod 0644, $_; } is equivalent to open(FOO, "echo .c \| tr -s ' \t\r\f' '\\012\\012\\012\\012'\|"); while (<FOO>) { chop; chmod 0644, $_; } In fact, it's currently implemented that way. (Which means it will not work on filenames with spaces in them unless you have csh(1) on your machine.)` [download]	[reply] [d/l]

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RE: Re: More on directory recursion
by takshaka (Friar) on Jun 12, 2000 at 22:51 UTC

5.6, however, implements glob internally through File::Glob, so it's a lot safer (though that feature is currently labelled "experimental").

Update: This snippet from perlop should make it clear what is going on with glob on pre-5.6 Perl:

while (<*.c>) {
        chmod 0644, $_;
    }

is equivalent to

    open(FOO, "echo *.c | tr -s ' \t\r\f' '\\012\\012\\012\\012'|");
    while (<FOO>) {
        chop;
        chmod 0644, $_;
    }

In fact, it's currently implemented that way.  (Which
means it will not work on filenames with spaces in them
unless you have csh(1) on your machine.)
[download]

[reply]
[d/l]