Section 12.3. An Alternate Syntax for Globbing

12.3. An Alternate Syntax for Globbing

Though we use the term globbing freely, and we talk about the glob operator, you might not see the word glob in many of the programs that use globbing. Why not? Well, most legacy code was written before the glob operator was given a name. Instead, it was called up by the angle-bracket syntax, similar to reading from a filehandle:

     my @all_files = <*>; ## exactly the same as my @all_files = glob "*"; 

The value between the angle brackets is interpolated similarly to a double-quoted string, which means that Perl variables are expanded to their current Perl values before being globbed:

     my $dir = "/etc";     my @dir_files = <$dir/* $dir/.*>; 

Here, we've fetched all the non-dot and dot files from the designated directory because $dir has been expanded to its current value.

Since using angle brackets means both filehandle reading and globbing, how does Perl decide which of the two operators to use? Well, a filehandle has to be a Perl identifier. If the item between the angle brackets is strictly a Perl identifier, it'll be a filehandle read; otherwise, it'll be a globbing operation, as in this example:

     my @files = <FRED/*>;  ## a glob     my @lines = <FRED>;    ## a filehandle read     my $name = "FRED";     my @files = <$name/*>; ## a glob 

The one exception is if the contents are a simple scalar variable (not an element of a hash or array), then it's an indirect filehandle read,[*] where the variable contents give the name of the filehandle you want to read:

[*] If the indirect handle is a text string, then it's subject to the "symbolic reference" test that is forbidden under use strict. However, the indirect handle might be a typeglob or reference to an I/O object, which means it would work under use strict.

     my $name = "FRED";     my @lines = <$name>; ## an indirect filehandle read of FRED handle 

Determining if it's a glob or a filehandle read is done at compile time so it's independent of the content of the variables.

If you want, you can get the operation of an indirect filehandle read using the readline operator,[] which makes it clearer:

] If youre using Perl 5.005 or later.

     my $name = "FRED";     my @lines = readline FRED;  ## read from FRED     my @lines = readline $name; ## read from FRED 

But the readline operator is rarely used, as indirect filehandle reads are uncommon and are generally performed against a simple scalar variable anyway.

Learning Perl
Learning Perl, 5th Edition
ISBN: 0596520107
EAN: 2147483647
Year: 2003
Pages: 232

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