# The Julia REPL Julia comes with a full-featured interactive command-line REPL (read-eval-print loop) built into the `julia` executable. In addition to allowing quick and easy evaluation of Julia statements, it has a searchable history, tab-completion, many helpful keybindings, and dedicated help and shell modes. The REPL can be started by simply calling `julia` with no arguments or double-clicking on the executable: ```@eval io = IOBuffer() Base.banner(io) banner = String(take!(io)) import Markdown Markdown.parse("```\n\$ julia\n\n$(banner)\njulia>\n```") ``` To exit the interactive session, type `^D` -- the control key together with the `d` key on a blank line -- or type `exit()` followed by the return or enter key. The REPL greets you with a banner and a `julia>` prompt. ## The different prompt modes ### The Julian mode The REPL has five main modes of operation. The first and most common is the Julian prompt. It is the default mode of operation; each new line initially starts with `julia>`. It is here that you can enter Julia expressions. Hitting return or enter after a complete expression has been entered will evaluate the entry and show the result of the last expression. ```jldoctest julia> string(1 + 2) "3" ``` There are a number useful features unique to interactive work. In addition to showing the result, the REPL also binds the result to the variable `ans`. A trailing semicolon on the line can be used as a flag to suppress showing the result. ```jldoctest julia> string(3 * 4); julia> ans "12" ``` In Julia mode, the REPL supports something called *prompt pasting*. This activates when pasting text that starts with `julia> ` into the REPL. In that case, only expressions starting with `julia> ` are parsed, others are removed. This makes it possible to paste a chunk of code that has been copied from a REPL session without having to scrub away prompts and outputs. This feature is enabled by default but can be disabled or enabled at will with `REPL.enable_promptpaste(::Bool)`. If it is enabled, you can try it out by pasting the code block above this paragraph straight into the REPL. This feature does not work on the standard Windows command prompt due to its limitation at detecting when a paste occurs. Objects are printed at the REPL using the [`show`](@ref) function with a specific [`IOContext`](@ref). In particular, the `:limit` attribute is set to `true`. Other attributes can receive in certain `show` methods a default value if it's not already set, like `:compact`. It's possible, as an experimental feature, to specify the attributes used by the REPL via the `Base.active_repl.options.iocontext` dictionary (associating values to attributes). For example: ```julia-repl julia> rand(2, 2) 2×2 Array{Float64,2}: 0.8833 0.329197 0.719708 0.59114 julia> show(IOContext(stdout, :compact => false), "text/plain", rand(2, 2)) 0.43540323669187075 0.15759787870609387 0.2540832269192739 0.4597637838786053 julia> Base.active_repl.options.iocontext[:compact] = false; julia> rand(2, 2) 2×2 Array{Float64,2}: 0.2083967319174056 0.13330606013126012 0.6244375177790158 0.9777957560761545 ``` In order to define automatically the values of this dictionary at startup time, one can use the [`atreplinit`](@ref) function in the `~/.julia/config/startup.jl` file, for example: ```julia atreplinit() do repl repl.options.iocontext[:compact] = false end ``` ### Help mode When the cursor is at the beginning of the line, the prompt can be changed to a help mode by typing `?`. Julia will attempt to print help or documentation for anything entered in help mode: ```julia-repl julia> ? # upon typing ?, the prompt changes (in place) to: help?> help?> string search: string String Cstring Cwstring RevString randstring bytestring SubString string(xs...) Create a string from any values using the print function. ``` Macros, types and variables can also be queried: ``` help?> @time @time A macro to execute an expression, printing the time it took to execute, the number of allocations, and the total number of bytes its execution caused to be allocated, before returning the value of the expression. See also @timev, @timed, @elapsed, and @allocated. help?> Int32 search: Int32 UInt32 Int32 <: Signed 32-bit signed integer type. ``` A string or regex literal searches all docstrings using [`apropos`](@ref): ``` help?> "aprop" REPL.stripmd Base.Docs.apropos help?> r"ap..p" Base.:∘ Base.shell_escape_posixly Distributed.CachingPool REPL.stripmd Base.Docs.apropos ``` Help mode can be exited by pressing backspace at the beginning of the line. ### [Shell mode](@id man-shell-mode) Just as help mode is useful for quick access to documentation, another common task is to use the system shell to execute system commands. Just as `?` entered help mode when at the beginning of the line, a semicolon (`;`) will enter the shell mode. And it can be exited by pressing backspace at the beginning of the line. ```julia-repl julia> ; # upon typing ;, the prompt changes (in place) to: shell> shell> echo hello hello ``` !!! note For Windows users, Julia's shell mode does not expose windows shell commands. Hence, this will fail: ```julia-repl julia> ; # upon typing ;, the prompt changes (in place) to: shell> shell> dir ERROR: IOError: could not spawn `dir`: no such file or directory (ENOENT) Stacktrace! ....... ``` However, you can get access to `PowerShell` like this: ```julia-repl julia> ; # upon typing ;, the prompt changes (in place) to: shell> shell> powershell Windows PowerShell Copyright (C) Microsoft Corporation. All rights reserved. PS C:\Users\elm> ``` ... and to `cmd.exe` like that (see the `dir` command): ```julia-repl julia> ; # upon typing ;, the prompt changes (in place) to: shell> shell> cmd Microsoft Windows [version 10.0.17763.973] (c) 2018 Microsoft Corporation. All rights reserved. C:\Users\elm>dir Volume in drive C has no label Volume Serial Number is 1643-0CD7 Directory of C:\Users\elm 29/01/2020 22:15 . 29/01/2020 22:15 .. 02/02/2020 08:06 .atom ``` ### Pkg mode The Package manager mode accepts specialized commands for loading and updating packages. It is entered by pressing the `]` key at the Julian REPL prompt and exited by pressing CTRL-C or pressing the backspace key at the beginning of the line. The prompt for this mode is `pkg>`. It supports its own help-mode, which is entered by pressing `?` at the beginning of the line of the `pkg>` prompt. The Package manager mode is documented in the Pkg manual, available at [https://julialang.github.io/Pkg.jl/v1/](https://julialang.github.io/Pkg.jl/v1/). ### Search modes In all of the above modes, the executed lines get saved to a history file, which can be searched. To initiate an incremental search through the previous history, type `^R` -- the control key together with the `r` key. The prompt will change to ```(reverse-i-search)`':```, and as you type the search query will appear in the quotes. The most recent result that matches the query will dynamically update to the right of the colon as more is typed. To find an older result using the same query, simply type `^R` again. Just as `^R` is a reverse search, `^S` is a forward search, with the prompt ```(i-search)`':```. The two may be used in conjunction with each other to move through the previous or next matching results, respectively. ## Key bindings The Julia REPL makes great use of key bindings. Several control-key bindings were already introduced above (`^D` to exit, `^R` and `^S` for searching), but there are many more. In addition to the control-key, there are also meta-key bindings. These vary more by platform, but most terminals default to using alt- or option- held down with a key to send the meta-key (or can be configured to do so), or pressing Esc and then the key. | Keybinding | Description | |:------------------- |:---------------------------------------------------------------------------------------------------------- | | **Program control** |   | | `^D` | Exit (when buffer is empty) | | `^C` | Interrupt or cancel | | `^L` | Clear console screen | | Return/Enter, `^J` | New line, executing if it is complete | | meta-Return/Enter | Insert new line without executing it | | `?` or `;` | Enter help or shell mode (when at start of a line) | | `^R`, `^S` | Incremental history search, described above | | **Cursor movement** |   | | Right arrow, `^F` | Move right one character | | Left arrow, `^B` | Move left one character | | ctrl-Right, `meta-F`| Move right one word | | ctrl-Left, `meta-B` | Move left one word | | Home, `^A` | Move to beginning of line | | End, `^E` | Move to end of line | | Up arrow, `^P` | Move up one line (or change to the previous history entry that matches the text before the cursor) | | Down arrow, `^N` | Move down one line (or change to the next history entry that matches the text before the cursor) | | Shift-Arrow Key | Move cursor according to the direction of the Arrow key, while activating the region ("shift selection") | | Page-up, `meta-P` | Change to the previous history entry | | Page-down, `meta-N` | Change to the next history entry | | `meta-<` | Change to the first history entry (of the current session if it is before the current position in history) | | `meta->` | Change to the last history entry | | `^-Space` | Set the "mark" in the editing region (and de-activate the region if it's active) | | `^-Space ^-Space` | Set the "mark" in the editing region and make the region "active", i.e. highlighted | | `^G` | De-activate the region (i.e. make it not highlighted) | | `^X^X` | Exchange the current position with the mark | | **Editing** |   | | Backspace, `^H` | Delete the previous character, or the whole region when it's active | | Delete, `^D` | Forward delete one character (when buffer has text) | | meta-Backspace | Delete the previous word | | `meta-d` | Forward delete the next word | | `^W` | Delete previous text up to the nearest whitespace | | `meta-w` | Copy the current region in the kill ring | | `meta-W` | "Kill" the current region, placing the text in the kill ring | | `^K` | "Kill" to end of line, placing the text in the kill ring | | `^Y` | "Yank" insert the text from the kill ring | | `meta-y` | Replace a previously yanked text with an older entry from the kill ring | | `^T` | Transpose the characters about the cursor | | `meta-Up arrow` | Transpose current line with line above | | `meta-Down arrow` | Transpose current line with line below | | `meta-u` | Change the next word to uppercase | | `meta-c` | Change the next word to titlecase | | `meta-l` | Change the next word to lowercase | | `^/`, `^_` | Undo previous editing action | | `^Q` | Write a number in REPL and press `^Q` to open editor at corresponding stackframe or method | | `meta-Left Arrow` | indent the current line on the left | | `meta-Right Arrow` | indent the current line on the right | | `meta-.` | insert last word from previous history entry | ### Customizing keybindings Julia's REPL keybindings may be fully customized to a user's preferences by passing a dictionary to `REPL.setup_interface`. The keys of this dictionary may be characters or strings. The key `'*'` refers to the default action. Control plus character `x` bindings are indicated with `"^x"`. Meta plus `x` can be written `"\\M-x"` or `"\ex"`, and Control plus `x` can be written `"\\C-x"` or `"^x"`. The values of the custom keymap must be `nothing` (indicating that the input should be ignored) or functions that accept the signature `(PromptState, AbstractREPL, Char)`. The `REPL.setup_interface` function must be called before the REPL is initialized, by registering the operation with [`atreplinit`](@ref) . For example, to bind the up and down arrow keys to move through history without prefix search, one could put the following code in `~/.julia/config/startup.jl`: ```julia import REPL import REPL.LineEdit const mykeys = Dict{Any,Any}( # Up Arrow "\e[A" => (s,o...)->(LineEdit.edit_move_up(s) || LineEdit.history_prev(s, LineEdit.mode(s).hist)), # Down Arrow "\e[B" => (s,o...)->(LineEdit.edit_move_down(s) || LineEdit.history_next(s, LineEdit.mode(s).hist)) ) function customize_keys(repl) repl.interface = REPL.setup_interface(repl; extra_repl_keymap = mykeys) end atreplinit(customize_keys) ``` Users should refer to `LineEdit.jl` to discover the available actions on key input. ## Tab completion In both the Julian and help modes of the REPL, one can enter the first few characters of a function or type and then press the tab key to get a list all matches: ```julia-repl julia> stri[TAB] stride strides string strip julia> Stri[TAB] StridedArray StridedMatrix StridedVecOrMat StridedVector String ``` The tab key can also be used to substitute LaTeX math symbols with their Unicode equivalents, and get a list of LaTeX matches as well: ```julia-repl julia> \pi[TAB] julia> π π = 3.1415926535897... julia> e\_1[TAB] = [1,0] julia> e₁ = [1,0] 2-element Array{Int64,1}: 1 0 julia> e\^1[TAB] = [1 0] julia> e¹ = [1 0] 1×2 Array{Int64,2}: 1 0 julia> \sqrt[TAB]2 # √ is equivalent to the sqrt function julia> √2 1.4142135623730951 julia> \hbar[TAB](h) = h / 2\pi[TAB] julia> ħ(h) = h / 2π ħ (generic function with 1 method) julia> \h[TAB] \hat \hermitconjmatrix \hkswarow \hrectangle \hatapprox \hexagon \hookleftarrow \hrectangleblack \hbar \hexagonblack \hookrightarrow \hslash \heartsuit \hksearow \house \hspace julia> α="\alpha[TAB]" # LaTeX completion also works in strings julia> α="α" ``` A full list of tab-completions can be found in the [Unicode Input](@ref) section of the manual. Completion of paths works for strings and julia's shell mode: ```julia-repl julia> path="/[TAB]" .dockerenv .juliabox/ boot/ etc/ lib/ media/ opt/ root/ sbin/ sys/ usr/ .dockerinit bin/ dev/ home/ lib64/ mnt/ proc/ run/ srv/ tmp/ var/ shell> /[TAB] .dockerenv .juliabox/ boot/ etc/ lib/ media/ opt/ root/ sbin/ sys/ usr/ .dockerinit bin/ dev/ home/ lib64/ mnt/ proc/ run/ srv/ tmp/ var/ ``` Tab completion can help with investigation of the available methods matching the input arguments: ```julia-repl julia> max([TAB] # All methods are displayed, not shown here due to size of the list julia> max([1, 2], [TAB] # All methods where `Vector{Int}` matches as first argument max(x, y) in Base at operators.jl:215 max(a, b, c, xs...) in Base at operators.jl:281 julia> max([1, 2], max(1, 2), [TAB] # All methods matching the arguments. max(x, y) in Base at operators.jl:215 max(a, b, c, xs...) in Base at operators.jl:281 ``` Keywords are also displayed in the suggested methods after `;`, see below line where `limit` and `keepempty` are keyword arguments: ```julia-repl julia> split("1 1 1", [TAB] split(str::AbstractString; limit, keepempty) in Base at strings/util.jl:302 split(str::T, splitter; limit, keepempty) where T<:AbstractString in Base at strings/util.jl:277 ``` The completion of the methods uses type inference and can therefore see if the arguments match even if the arguments are output from functions. The function needs to be type stable for the completion to be able to remove non-matching methods. Tab completion can also help completing fields: ```julia-repl julia> import UUIDs julia> UUIDs.uuid[TAB] uuid1 uuid4 uuid_version ``` Fields for output from functions can also be completed: ```julia-repl julia> split("","")[1].[TAB] lastindex offset string ``` The completion of fields for output from functions uses type inference, and it can only suggest fields if the function is type stable. Dictionary keys can also be tab completed: ```julia-repl julia> foo = Dict("qwer1"=>1, "qwer2"=>2, "asdf"=>3) Dict{String,Int64} with 3 entries: "qwer2" => 2 "asdf" => 3 "qwer1" => 1 julia> foo["q[TAB] "qwer1" "qwer2" julia> foo["qwer ``` ## Customizing Colors The colors used by Julia and the REPL can be customized, as well. To change the color of the Julia prompt you can add something like the following to your `~/.julia/config/startup.jl` file, which is to be placed inside your home directory: ```julia function customize_colors(repl) repl.prompt_color = Base.text_colors[:cyan] end atreplinit(customize_colors) ``` The available color keys can be seen by typing `Base.text_colors` in the help mode of the REPL. In addition, the integers 0 to 255 can be used as color keys for terminals with 256 color support. You can also change the colors for the help and shell prompts and input and answer text by setting the appropriate field of `repl` in the `customize_colors` function above (respectively, `help_color`, `shell_color`, `input_color`, and `answer_color`). For the latter two, be sure that the `envcolors` field is also set to false. It is also possible to apply boldface formatting by using `Base.text_colors[:bold]` as a color. For instance, to print answers in boldface font, one can use the following as a `~/.julia/config/startup.jl`: ```julia function customize_colors(repl) repl.envcolors = false repl.answer_color = Base.text_colors[:bold] end atreplinit(customize_colors) ``` You can also customize the color used to render warning and informational messages by setting the appropriate environment variables. For instance, to render error, warning, and informational messages respectively in magenta, yellow, and cyan you can add the following to your `~/.julia/config/startup.jl` file: ```julia ENV["JULIA_ERROR_COLOR"] = :magenta ENV["JULIA_WARN_COLOR"] = :yellow ENV["JULIA_INFO_COLOR"] = :cyan ``` ## TerminalMenus TerminalMenus is a submodule of the Julia REPL and enables small, low-profile interactive menus in the terminal. ### Examples ```julia import REPL using REPL.TerminalMenus options = ["apple", "orange", "grape", "strawberry", "blueberry", "peach", "lemon", "lime"] ``` #### RadioMenu The RadioMenu allows the user to select one option from the list. The `request` function displays the interactive menu and returns the index of the selected choice. If a user presses 'q' or `ctrl-c`, `request` will return a `-1`. ```julia # `pagesize` is the number of items to be displayed at a time. # The UI will scroll if the number of options is greater # than the `pagesize` menu = RadioMenu(options, pagesize=4) # `request` displays the menu and returns the index after the # user has selected a choice choice = request("Choose your favorite fruit:", menu) if choice != -1 println("Your favorite fruit is ", options[choice], "!") else println("Menu canceled.") end ``` Output: ``` Choose your favorite fruit: ^ grape strawberry > blueberry v peach Your favorite fruit is blueberry! ``` #### MultiSelectMenu The MultiSelectMenu allows users to select many choices from a list. ```julia # here we use the default `pagesize` 10 menu = MultiSelectMenu(options) # `request` returns a `Set` of selected indices # if the menu us canceled (ctrl-c or q), return an empty set choices = request("Select the fruits you like:", menu) if length(choices) > 0 println("You like the following fruits:") for i in choices println(" - ", options[i]) end else println("Menu canceled.") end ``` Output: ``` Select the fruits you like: [press: d=done, a=all, n=none] [ ] apple > [X] orange [X] grape [ ] strawberry [ ] blueberry [X] peach [ ] lemon [ ] lime You like the following fruits: - orange - grape - peach ``` ### Customization / Configuration #### ConfiguredMenu subtypes Starting with Julia 1.6, the recommended way to configure menus is via the constructor. For instance, the default multiple-selection menu ``` julia> menu = MultiSelectMenu(options, pagesize=5); julia> request(menu) # ASCII is used by default [press: d=done, a=all, n=none] [ ] apple [X] orange [ ] grape > [X] strawberry v [ ] blueberry ``` can instead be rendered with Unicode selection and navigation characters with ```julia julia> menu = MultiSelectMenu(options, pagesize=5, charset=:unicode); julia> request(menu) [press: d=done, a=all, n=none] ⬚ apple ✓ orange ⬚ grape → ✓ strawberry ↓ ⬚ blueberry ``` More fine-grained configuration is also possible: ```julia julia> menu = MultiSelectMenu(options, pagesize=5, charset=:unicode, checked="YEP!", unchecked="NOPE", cursor='⧐'); julia> request(menu) julia> request(menu) [press: d=done, a=all, n=none] NOPE apple YEP! orange NOPE grape ⧐ YEP! strawberry ↓ NOPE blueberry ``` Aside from the overall `charset` option, for `RadioMenu` the configurable options are: - `cursor::Char='>'|'→'`: character to use for cursor - `up_arrow::Char='^'|'↑'`: character to use for up arrow - `down_arrow::Char='v'|'↓'`: character to use for down arrow - `updown_arrow::Char='I'|'↕'`: character to use for up/down arrow in one-line page - `scroll_wrap::Bool=false`: optionally wrap-around at the beginning/end of a menu - `ctrl_c_interrupt::Bool=true`: If `false`, return empty on ^C, if `true` throw InterruptException() on ^C `MultiSelectMenu` adds: - `checked::String="[X]"|"✓"`: string to use for checked - `unchecked::String="[ ]"|"⬚")`: string to use for unchecked You can create new menu types of your own. Types that are derived from `TerminalMenus.ConfiguredMenu` configure the menu options at construction time. #### Legacy interface Prior to Julia 1.6, and still supported throughout Julia 1.x, one can also configure menus by calling `TerminalMenus.config()`. ## References ### REPL ```@docs Base.atreplinit ``` ### TerminalMenus #### Configuration ```@docs REPL.TerminalMenus.Config REPL.TerminalMenus.MultiSelectConfig REPL.TerminalMenus.config ``` #### User interaction ```@docs REPL.TerminalMenus.request ``` #### AbstractMenu extension interface Any subtype of `AbstractMenu` must be mutable, and must contain the fields `pagesize::Int` and `pageoffset::Int`. Any subtype must also implement the following functions: ```@docs REPL.TerminalMenus.pick REPL.TerminalMenus.cancel REPL.TerminalMenus.writeline ``` It must also implement either `options` or `numoptions`: ```@docs REPL.TerminalMenus.options REPL.TerminalMenus.numoptions ``` If the subtype does not have a field named `selected`, it must also implement ```@docs REPL.TerminalMenus.selected ``` The following are optional but can allow additional customization: ```@docs REPL.TerminalMenus.header REPL.TerminalMenus.keypress ```