A little introduction to Filename Globbing

There are many ways to interact over filenames. One of the most flexible is file globbing.

File globbing is a way to aquire filenames from your harddisk without having to run trought a directory tree. From the perlop manual:

If what's within the angle brackets is neither a filehandle nor a simple scalar variable containing a filehandle name, typeglob, or typeglob reference, it is interpreted as a filename pattern to be globbed, and either a list of filenames or the next filename in the list is returned, depending on context. This distinction is determined on syntactic grounds alone. That means "<$x>" is always a readline() from an indirect handle, but "<$hash{key}>" is always a glob(). That's because $x is a simple scalar variable, but $hash{key} is not--it's a hash element.

One level of double-quote interpretation is done first, but you can't say "<$foo>" because that's an indirect filehandle as explained in the previous paragraph. (In older versions of Perl, programmers would insert curly brackets to force interpretation as a filename glob: "<${foo}>". These days, it's considered cleaner to call the internal function directly as "glob($foo)", which is probably the right way to have done it in the first place.) For example:

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

is roughly equivalent to:

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

except that the globbing is actually done internally using the standard "File::Glob" extension. Of course, the shortest way to do the above is:

chmod 0644, <*.c>;

And that's it. I think you would like to take a deeper look at the perlop manual, and read more about this operator. Feel free to post a new question at Seekers of Perl Wisdom or ask me directly about this.

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Just Another Perl Monk

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