File-related operations

Here we present a quick overview of the file-related input/output operations. Details can be found in the documentation for the IO role, as well as the IO::Handle and IO::Path types.

Reading from files

One way to read the contents of a file is to open the file via the open function with the :r (read) file mode option and slurp in the contents:

my $fh = open "testfile":r;
my $contents = $fh.slurp-rest;

Here we explicitly close the file handle using the close method on the IO::Handle object. This is a very traditional way of reading the contents of a file. However, the same can be done more easily and clearly like so:

my $contents = "testfile".IO.slurp;
# or in procedural form: 
$contents = slurp "testfile"

By adding the IO role to the file name string, we are effectively able to refer to the string as the file object itself and thus slurp in its contents directly. Note that the slurp takes care of opening and closing the file for you.

Line by line

Of course, we also have the option to read a file line-by-line. The new line separator (i.e., $* will be excluded.

for 'huge-csv'.IO.lines -> $line {
    # Do something with $line 
# or if you'll be processing later 
my @lines = 'huge-csv'.IO.lines;

Writing to files

To write data to a file, again we have the choice of the traditional method of calling the open function – this time with the :w (write) option -- and printing the data to the file:

my $fh = open "testfile":w;
$fh.print("data and stuff\n");

Or equivalently with say, thus the explicit newline is no longer necessary:

my $fh = open "testfile":w;
$fh.say("data and stuff");

We can simplify this by using spurt to open the file in write mode, writing the data to the file and closing it again for us:

spurt "testfile""data and stuff\n";

By default all (text) files are written as UTF-8, however if necessary, an explicit encoding can be specified via the :enc option:

spurt "testfile""latin1 text: äöüß"enc => "latin1";

To write formatted strings to a file, use the printf function of IO::Handle.

my $fh = open "testfile":w;
$fh.printf("formatted data %04d\n"42);

To append to a file, specify the :a option when opening the file handle explicitly,

my $fh = open "testfile":a;
$fh.print("more data\n");

or equivalently with say, thus the explicit newline is no longer necessary,

my $fh = open "testfile":a;
$fh.say("more data");

or even simpler with the :append option in the call to spurt:

spurt "testfile""more data\n":append;

To explicitly write binary data to a file, open it with the :bin option. The input/output operations then will take place using the Buf type instead of the Str type.

Copying and renaming files

Routines copy, rename, and move are available to avoid low-level system commands. See details at copy, rename, and move. Some examples:

my $filea = 'foo';
my $fileb = 'foo.bak';
my $filec = '/disk1/foo';  # note 'diskN' is assumed to be a physical storage device 
copy $filea$fileb;              # overwrites $fileb if it exists 
copy $filea$fileb:createonly# fails if $fileb exists 
rename $filea'new-foo';              # overwrites 'new-foo' if it exists 
rename $filea'new-foo':createonly# fails if 'new-foo' exists 
# use move when a system-level rename may not work 
move $fileb'/disk2/foo';              # overwrites '/disk2/foo' if it exists 
move $fileb'/disk2/foo':createonly# fails if '/disk2/foo' exists 

Checking files and directories

Use the e method on an IO::Handle object to test whether the file or directory exists.

if "nonexistent_file".IO.e {
    say "file exists";
else {
    say "file doesn't exist";

It is also possible to use the colon pair syntax to achieve the same thing:

if "path/to/file".IO ~~ :e {
    say 'file exists';
my $file = "path/to/file";
if $file.IO ~~ :e {
    say 'file exists';

Similarly to the file existence check, one can also check to see if a path is a directory. For instance, assuming that the file testfile and the directory lib exist, we would obtain from the existence test method e the same result, namely that both exist:

say "testfile".IO.e;  # OUTPUT: «True␤» 
say "lib".IO.e;       # OUTPUT: «True␤» 

However, since only one of them is a directory, the directory test method d will give a different result:

say "testfile".IO.d;  # OUTPUT: «False␤» 
say "lib".IO.d;       # OUTPUT: «True␤» 

Naturally the tables are turned if we check to see if the path is a file via the file test method f:

say "testfile".IO.f;  # OUTPUT: «True␤» 
say "lib".IO.f;       # OUTPUT: «False␤» 

There are other methods that can be used to query a file or directory, some useful ones are:

my $f = "file";
say $f.IO.modified# return time of last file (or directory) change 
say $f.IO.accessed# return last time file (or directory) was read 
say $f.IO.s;        # return size of file (or directory inode) in bytes 

See more methods and details at IO::Path.

Getting a directory listing

To list the contents of the current directory, use the dir function. It returns a list of IO::Path objects.

say dir;          # OUTPUT: «"/path/to/testfile".IO "/path/to/lib".IO␤» 

To list the files and directories in a given directory, simply pass a path as an argument to dir:

say dir "/etc/";  # OUTPUT: «"/etc/".IO "/etc/shadow".IO ....␤» 

Creating and removing directories

To create a new directory, simply call the mkdir function with the directory name as its argument:

mkdir "newdir";

The function returns the name of the created directory on success and Nil on failure. Thus the standard Perl idiom works as expected:

mkdir "newdir" or die "$!";

Use rmdir to remove empty directories:

rmdir "newdir" or die "$!";