No matter what kind of code base you end up working on, there's always some logic that has to deal with file paths. Sometimes we need to know the location of a certain file or a certain folder. On other occasions, we might need to create a path to a folder. Also, it's usually considered a bad practice to use hard-coded paths in your code, especially when it's going to be deployed elsewhere. For such needs, you should rely on programmatically generating relative paths.

Julia provides a lot of built-in functionality to interact with the host filesystem. Let's have a look at some of them with useful examples.

Print working directory

julia> pwd()
"/home/vikas/Downloads"

Get the contents of a directory

julia> readdir(pwd())
16-element Vector{String}:
 "0001-pinctrl-sunrisepoint-Add-missing-Interrupt-Status-re.patch"
 "20230423_150150.jpg"
 "20230423_170112.jpg"
 "20230425_222307.jpg"
 "20230428_233929.jpg"
 "BIOS_IMG.rcv"
 "DALL·E 2023-05-01 20.53.45 - An" ⋯ 92 bytes ⋯ "and some code on the screen.png"
 "DALL·E 2023-05-01 23.03.10 - An" ⋯ 56 bytes ⋯ "track with fire behind them.png"
...

Notice that readdir() returns an array of strings. This immediately allows us to perform additional operations such as filtering for a given file type:

julia> filter(x -> endswith(x, ".jpg"), readdir(pwd()))
4-element Vector{String}:
 "20230423_150150.jpg"
 "20230423_170112.jpg"
 "20230425_222307.jpg"
 "20230428_233929.jpg"

Using the join keyword, full paths to the files can be determined:

julia> readdir(join = true)
17-element Vector{String}:
 "/home/vikas/Downloads/0001-pinc" ⋯ 23 bytes ⋯ "ssing-Interrupt-Status-re.patch"
 "/home/vikas/Downloads/20230423_150150.jpg"
 "/home/vikas/Downloads/20230423_170112.jpg"
 "/home/vikas/Downloads/20230425_222307.jpg"
 "/home/vikas/Downloads/20230428_233929.jpg"
 "/home/vikas/Downloads/BIOS_IMG.rcv"
...

Check if a file exists

julia> isfile("julia-logo-color.png")
true

Check if a directory exists

julia> isdir("amazing_blog")
false

julia> mkdir("amazing_blog")
"amazing_blog"

julia> isdir("amazing_blog")
true

Get directory name from path

julia> current_location = pwd()
"/home/vikas/Downloads"

julia> dirname(current_location)
"/home/vikas"

julia> basename(current_location)
"Downloads"

Create a deep nested directory

mkpath can be used to create intermediate folders to a deeply nested path as shown below:

julia> mkpath(["amazing_blog", "folder_1", "folder_11", "folder_111"] |> joinpath)
"amazing_blog/folder_1/folder_11/folder_111"

julia> isdir("amazing_blog/folder_1/folder_11/folder_111")
true

Split a path

Sometimes, it's needed to extract some useful information from a given path. For such cases, splitpath is your friend:

julia> splitpath(current_location)
4-element Vector{String}:
 "/"
 "home"
 "vikas"
 "Downloads"

Join a path

julia> parts = splitpath(current_location)
4-element Vector{String}:
 "/"
 "home"
 "vikas"
 "Downloads"

julia> joinpath(parts)
"/home/vikas/Downloads"

This is extremely useful since the path separator is determined based on the operating system (Linux or Windows). In case you do need to specify a path in a code base that will be used both on Linux and Windows, it's way more robust to make use of joinpath.

Get current directory w.r.t. a file

The @__DIR__ macro can be used to determine the path to a file from where it's called. This is useful to safely add a relative path to a file or folder for which you are certain that the location would remain unchanged.

julia> pwd()
"/home/vikas/Downloads/amazing_blog"

julia> joinpath(@__DIR__, "..", "20230425_222307.jpg")
"/home/vikas/Downloads/amazing_blog/../20230425_222307.jpg"

julia> joinpath(@__DIR__, "..", "20230425_222307.jpg") |> isfile
true

Traversing through a directory tree

Using walkdir, we can surf through all the files within a folder, and perform operations such as finding files that match a certain name. For example, let's find files that have "README" in the name:

julia> pwd()
"/home/vikas"

julia> for (root, dirs, files) in walkdir("Desktop")
          for file in files
              if occursin("READ", file)
                  joinpath(root, file) |> println
              end
          end
       end
Desktop/Julia_release/julia-1.8.5/share/julia/stdlib/v1.8/ArgTools/README.md
Desktop/Julia_release/julia-1.8.5/share/julia/stdlib/v1.8/Downloads/README.md
Desktop/Julia_release/julia-1.8.5/share/julia/stdlib/v1.8/LibCURL/README.md
...

Conclusion

Julia has excellent support for handling paths to files and folders. The above examples are some of my most routinely used functions. A more comprehensive list can be found in the official documentation. I hope you learned something new today. Don't forget to bookmark this post and share it with fellow Julia nerds.