Interacting With Julia¶

The Julian mode¶

The REPL has four 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.

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.

julia>string(3*4);julia>ans"12"

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>?# upon typing ?, the prompt changes (in place) to: help>help>stringBase.string(xs...)Createastringfromanyvaluesusingthe"print"function.

In addition to function names, complete function calls may be entered to see which method is called for the given argument(s). Macros, types and variables can also be queried:

help>string(1)string(x::Union{Int16,Int128,Int8,Int32,Int64})atstring.jl:1553help>@printfBase.@printf([io::IOStream],"%Fmt",args...)Printarg(s)usingC"printf()"styleformatspecificationstring.Optionally,anIOStreammaybepassedasthefirstargumenttoredirectoutput.help>AbstractStringDataType:AbstractStringsupertype:Anysubtypes:Any[DirectIndexString,RepString,RevString{T<:AbstractString},SubString{T<:AbstractString},String]

Help mode can be exited by pressing backspace at the beginning of the line.

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>;# upon typing ;, the prompt changes (in place) to: shell>shell>echohellohello

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.

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 "\\Mx". 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(). For example, to bind the up and down arrow keys to move through history without prefix search, one could put the following code in .juliarc.jl:

importBase:LineEdit,REPLconstmykeys=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_up(s)||LineEdit.history_next(s,LineEdit.mode(s).hist)))function customize_keys(repl)repl.interface=REPL.setup_interface(repl;extra_repl_keymap=mykeys)endatreplinit(customize_keys)

Users should refer to base/LineEdit.jl to discover the available actions on key input.