Directory Operations

Globbing

If we want to see the list of the files in the current directory we run a command like dir or ls. If we do not need to see all files, but only some of them we can specify what kind of files we would like to see. For example, to get a list of all Perl scripts we can execute a command like dir *.pl

Perl has a special tool to provide the same service for inside scripts. This tool is called glob. This is a function that takes one argument a string with file name pattern and returns a list of files in the current directory with names matching this pattern. Patterns can contain symbols * (meaning: any number of letters or digits) and ? (meaning: any letter or digit). Thus, to get all Perl scripts in the current directory inside a Perl script we can use code like this 

my @scripts = glob("*.pl");
foreach (@scripts){ print "$_\n"; }
If we need to get the list of all files we need to use pattern "*". We also may specify a name of the directory where we want to get the list of files and then a pattern. For example, to print all files in a directory whose name is in variable $dir we do this: 
my $dir = "../oracle";
foreach ( glob("$dir/*") ){
  print "$_\n";
}

glob function also allows us to provide several patterns in one argument string, In this situation patterns should be separated with spaces. For example, the following code prints names of all files that start with p or s: 

for ( glob "p* s*" ){
  print "$_\n";
}

Manipulating Files and Directories

Changing directories

Our scripts always run in the current directory, which is the starting point for relative pathnames. That is, if we refer to file index.html, that means index.html in the current directory. The chdir operator changes the current directory. It works just like DOS/Unix cd command. This operator returns a boolean value:
  • true - upon success
  • and false if it failed. 
    chdir("/homes/james") or die("Cannot change a directory\n");
    If we omit the parameter, Perl determines the home directory as best possible and attempts to set the working directory to the home directory. This is one of few places where omitting the parameter doesn't use $_.

    Removing files

    Function unlink removes files in Perl. It takes a list of file names as arguments and returns the number of successfully deleted files. For example, the following code tries to remove files fred and wilma: 
    $deleted = unlink "fred", "wilma";
print "$deleted file(s) deleted.\n";
    We can also use any array containing file names as an argument of the function unlink or the result of the glob function. For example, we can remove all files from the current directory by running: 
    unlink glob "*";
    However, I wouldn't recommend to test such a script .

    Renaming files

    Giving an existing file a new name is simple with the rename function. This function takes two strings as its arguments - the first string contains the old file name and the second string contains the new file name. The rename function returns true if file was successfully renamed, and false if the function failed. The following example renames all files in the current directory rewriting their names in lower case characters: 
    for ( glob "*" ){
  unless( rename $_, lc($_) ){
    warn "Cannot rename file '$_' to '".lc($_)."'\n";
  }
}
    In this script we used two new functions:

    Using rename function we can also move files around. That is, our file names may include directories as well. For example, the following command moves file fred from directory /oracle into the current directory: 

    rename "/oracle/fred", "fred";

    Making and removing directories

    Perl also allows us to create and remove directories. To create a directory we can use function mkdir. This function takes two arguments:
  • the name of the directory to create
  • and permissions for the new directory.
    The second argument is optional.

    To remove a directory we need to use function rmdir. This function takes only one argument - the name of the directory to remove and returns true upon success, false on fail. Combining these two functions we can create a temporary directory for our script to work in and remove this directory when the job is done: 

    my $temp_dir = "$_my_script_temp_$";
mkdir $temp_dir;
chdir $temp_dir;
...
chdir "..";
rmdir $temp_dir;