dirctory operation: chdir, Globbing <>, opendir, readdir, closedir

chdir "/etc" or die " $!"; #change the directory to /etc/

foreach (@ARGV){
    print "one arg is $_\n";
}

perl glob.pl *.pl will list all files end with .pl.

foreach (glob "*.pl *.txt"){

print "one arg is $_\n";
}

this will list all files end with .pl and .txt.

An Alternate Syntax for Globbing <>  angle-bracket syntax
my @all_files = <*>; ## exactly the same as my @all_files = glob "*";
So, if 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.
So, if the item between the angle brackets is strictly a Perl identifier, it’s a filehandle
read; otherwise, it’s a globbing operation. For example:

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

readdir reads the content under the directory.

my $dirname = "/home/yliu/test/";
opendir DIR, $dirname or die "$!\n";
foreach (readdir DIR){
    next if (/^\./);
    print "$_\n";
}
closedir DIR;

Like filehandles, directory handles are automatically closed at the end of the program
or if the directory handle is reopened onto another directory.
chdir函数能够更改当前的工作目录。它不接受任何参数时，能将目录更改到用户的主目录中。如果调用成功，该函数将返回1，否则就返回0。系统错误代码将保存在Perl的$!变量中 。