How do I list the files in a directory?

Posted 2020-08-25 黄洪波写点东西的地方

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原文地址：How do I list the files in a directory?

You want a list of all the files, or all the files matching a certain pattern, or with a certain ending, in a directory

The solution

Reading directories is a bit like reading files. First you open the directory, then you read from it and then you close it. You use a directory handle much as you use a file handle.

Step 1: Opening the directory

To open the directory, we use a function called opendir. You use this much like the open function to open files. In the example below, we open the /tmp directory:

    #!/usr/bin/perl
    use strict;
    use warnings;

    my $directory = ‘/tmp‘;

    opendir (DIR, $directory) or die $!;

Step 2: Reading the directory

To read the files and directories in the directory we use the readdir function. readdir returns the name of each file or directory in the opened directory in turn when used in scalar context, or a list of the names of all files and directories in that directory when used in list context. This means that we can use readdir in a foreach loop (or any other loop construct):

    while (my $file = readdir(DIR)) {

        print "$file\n";

    }

Step 3: Closing the directory

We use the function closedir to close the directory once we are finished with it. Like files, the directory will be closed when the program terminates, but sometimes you will need to explicitly close the directory:

    closedir(DIR);

Directory Listing

Provided your program has sufficient access to the directory being read, readdir will list every file and directory contained in that directory. However, you often will not want all files or directories. For example, it is quite common to exclude all filenames beginning with a period:

    #!/usr/bin/perl

    use strict;
    use warnings;

    my $dir = ‘/tmp‘;

    opendir(DIR, $dir) or die $!;

    while (my $file = readdir(DIR)) {

        # Use a regular expression to ignore files beginning with a period
        next if ($file =~ m/^\./);

	print "$file\n";

    }

    closedir(DIR);
    exit 0;

See further down for a more compact way of doing this.

Find the directories

Sometimes you may want to find all the directories in a directory. Remember that readdir() gives you the names of the files and directories, not the paths. If you want to test a file using any of the standard file tests, you need to use the full path:

    #!/usr/bin/perl

    use strict;
    use warnings;

    my $dir = ‘/tmp‘;

    opendir(DIR, $dir) or die $!;

    while (my $file = readdir(DIR)) {

        # A file test to check that it is a directory
	# Use -f to test for a file
        next unless (-d "$dir/$file");

	print "$file\n";

    }

    closedir(DIR);
    exit 0;

Find files ending in...

Quite often you want to find all files ending in a given suffix. For example, you may want to find all files ending in .txt:

    #!/usr/bin/perl

    use strict;
    use warnings;

    my $dir = ‘/tmp‘;

    opendir(DIR, $dir) or die $!;

    while (my $file = readdir(DIR)) {

        # We only want files
        next unless (-f "$dir/$file");

        # Use a regular expression to find files ending in .txt
        next unless ($file =~ m/\.txt$/);

        print "$file\n";
    }

    closedir(DIR);
    exit 0;

An advanced example

A more advanced example is to use grep to filter out the files you want. The following example (based on a code sample from perldoc -f readdir) gets all the files (not directories) beginning with a period from the open directory. The filenames are found in the array @dots.

    #!/usr/bin/perl

    use strict;
    use warnings;

    my $dir = ‘/tmp‘;

    opendir(DIR, $dir) or die $!;

    my @dots 
        = grep { 
            /^\./             # Begins with a period
	    && -f "$dir/$_"   # and is a file
	} readdir(DIR);

    # Loop through the array printing out the filenames
    foreach my $file (@dots) {
        print "$file\n";
    }

    closedir(DIR);
    exit 0;

File::Find

You can use the File::Find module to recursively search through a directory (or directories). It is best used when you want to perform some operation on each file. See perldoc File::Find for more information.

glob

Another way of getting a directory listing - if you‘re only interested in the current directory and not in any sub-directories - is to use glob. You can pass glob a pattern (or patterns) to match and it will return any files that match. The example below will list all .pl and .pm files in the current directory:

    #!/usr/bin/perl

    use strict;
    use warnings;

    my @files = glob("*.pl *.pm");

    foreach my $file (@files) {

        print "$file\n";

    }

    exit 0;