# Expansions **URL:** \ **Category:** Manual++\ **Created:** [May 8, 2019, 2:16am UTC](https://discuss.kakoune.com/t/expansions/540 "2019-05-08T02:16:43Z")\ **Posts on this page:** 1\ **Page:** 1
**Author:** ![robertmeta](https://discuss.kakoune.com/user_avatar/discuss.kakoune.com/robertmeta/32/833_2.png) [@robertmeta](https://discuss.kakoune.com/u/robertmeta)\ **Post date:** [May 8, 2019, 2:16am UTC](https://discuss.kakoune.com/t/expansions/540/1 "2019-05-08T02:16:43Z")
While parsing a command (see [`:doc command-parsing`](https://discuss.kakoune.com/t/command-parsing/537/2)), Kakoune recognises certain patterns and will replace them with their associated value before executing the command. These patterns are called expansions. Every expansion consists of a `%`, followed by the expansion _type_ (one or more alphabetic characters), a quoting character, and then all the text up to and including its matching character. If a nestable punctuation character (`(`, `[`, `{`, or `<`) is used as the opening quoting character, the expansion will end at its matching opposite (`)`, `]`, `}`, or `>`). Nested pairs of the braces used in the expansion are allowed, but they must be balanced. Braces other than the ones used in the expansion need not be balanced, however. For example, `%{nest{ed} non[nested}` is valid and expands to `nest{ed} non[nested`. If any other character is used, the expansion will end at the next occurrence of that character. The quoting character can be escaped inside the expansion if it is doubled-up. For example, `%|abc||def|` expands to the text `abc|def`. It doesn’t matter which character is used, but `{}` are most common. There are 2 types of quoting which can be used to group together words separated by whitespace into a single argument or prevent expansions from expanding: “double quoted strings” Double quoted strings are mainly for grouping multiple `%` expansions or `%` expansions and regular text as a single argument. `%` and `"` can be escaped by doubling the characters (i.e. `%%` and `""`). _single quoted strings_ Expansions are not processed inside single quoted strings. Single quotes can be escaped by doubling up (i.e. `''`). Expansions are processed when unquoted and anywhere inside double-quoted strings, but not inside unquoted words, inside single-quoted strings, or inside %-strings or other expansions (see [`:doc command-parsing typed-expansions`](https://discuss.kakoune.com/t/command-parsing/537/2#typed-expansions) for full details). For example: - `echo %val{session}` echoes the current session ID - `echo x%val{session}x` echoes the literal text `x%val{session}x` - `echo '%val{session}'` echoes the literal text `%val{session}` - `echo "x%val{session}x"` echoes the current session ID, surrounded by `x` - `echo %{%val{session}}"` echoes the the literal text `%val{session}` - `echo %sh{ echo %val{session} }"` echoes the literal text `%val{session}` Like “variable expansion” and “command substitution” in shell programming, Kakoune expansions can expand to multiple “words” - that is, separate arguments on the resulting command-line. However, unlike shell programming, Kakoune expansions cannot _accidentally_ expand to multiple words because they contain whitespace or other special characters. Only expansions which semantically contain a list of values (list-type options, registers, selections, etc.) expand to multiple arguments. While in shell-programming it’s good practice to always wrap expansions in double-quotes, in Kakoune it’s perfectly safe to leave expansions unquoted. # Argument expansions Expansions with the type `arg` can only be used inside the “commands” parameter of the `define-command` command (See [`:doc commands declaring-new-commands`](https://discuss.kakoune.com/t/commands/538/2#declaring-new-commands)). The following expansions are available: (where _n_ is a decimal number) expands to argument number _n_ of the current command **%arg{@}** expands to all the arguments of the current command, as individual words # Option expansions Expansions with the type `opt` expand to the value associated with the named option in the current scope (See [`:doc options`](https://discuss.kakoune.com/t/options/549/2)). For example, `%opt{BOM}` expands to `utf8` or to `none`, according to the current state of the `BOM` option. # Register expansions Expansions with the type `reg` expand to the contents of the named register. For registers named after symbols (like the search register `/`), the expansion can use either the symbol or the alphabetic name (See [`:doc registers`](https://discuss.kakoune.com/t/registers/551/2)). For example, `%reg{/}` expands to the content of the `/` register, and so does `%reg{slash}`. # Shell expansions Expansions with the type `sh` are executed as shell-scripts, and whatever the script prints to standard output replaces the expansion. For example, the command `echo %sh{date}` will echo the output of the `date` command. > **Tip** > > If a shell expansion writes to standard error, that output is appended > to Kakoune’s `\*debug*` buffer. If you’re trying to debug a shell > expansion, check the debug buffer with `:buffer \*debug*` to see if > anything shows up. Because Kakoune does not expand expansions inside the text of an expansion, you can’t use normal expansions inside `%sh{}`. Instead, Kakoune can export expansions as environment variables to make them available to the shell. Here’s how expansion patterns map to variable names: (where _n_ is a decimal number) becomes `$_n_`. For example, `%arg{3}` becomes `$3`. **%arg{@}** becomes `$@` becomes `$kak_opt_x` (where _x_ is the alphabetic name of a register) `$kak_reg_x` contains all the selections in register _x_ `$kak_main_reg_x` contains only the main selection becomes `$kak_x` When turned into environment variables, list-type options, `$kak_reg_x`, and “quoted list” values will be shell-quoted so the shell doesn’t get confused about how many items the list contains. You will need to apply `eval` to get back the original values. For example, if you want to process the contents of each selection, you can do something like: ``` eval set -- "$kak_selections" while [$# -gt 0]; do # ... do a thing with $1 ... shift done ``` The `eval` command will take the expanded `$kak_selections` and unquote them, then execute the resulting `set` command, which sets the shell’s argument variables to the items from `$kak_selections`. The `while` loop with `shift` iterates through the arguments one by one. Only variables actually mentioned in the body of the shell expansion will be exported into the shell’s environment. For example: ``` echo %sh{ env | grep ^kak_ } ``` 1. will find none of Kakoune’s special environment variables, but: ``` echo %sh{ env | grep ^kak_ # kak_session } ``` 1. will find the `$kak_session` variable because it was mentioned by name in a comment, even though it wasn’t directly used. > **Tip** > > These environment variables are also available in other contexts where > Kakoune uses a shell command, such as the `|`, `!` or `$` normal mode > commands (See [`:doc keys`](https://discuss.kakoune.com/t/keys-keybindings/546/2)). # File expansions Expansions with the type `file` will expand to the content of the filename given in argument as read from the host filesystem. # Value expansions Expansions with the type `val` give access to Kakoune internal data that is not stored in an option or a register. Some value expansions can only be used in certain contexts, like `%val{hook_param}` that expands to the parameter string of the currently-executing hook, and is not available outside a hook. The following expansions are supported (with required context _in italics_): _in buffer, window scope_ full path of the file or same as `%val{bufname}` when there’s no associated file _in buffer, window scope_ number of lines in the current buffer quoted list of the names of currently-open buffers (as seen in `%val{bufname}`) _in buffer, window scope_ name of the current buffer _in window scope_ value of the `$X` environment variable in the client displaying the current window (e.g. `%val{client_env_SHELL}` is `$SHELL` in the client’s environment) unquoted list of the names of clients (as seen in `%val{client}`) connected to the current session _in window scope_ name of the client displaying the current window _in window scope_ process id of the client displaying the current window directory containing the user configuration _in `map` command \ parameter and `` from object menu_ current count when the mapping was triggered, defaults to 0 if no count given _in window scope_ offset of the main cursor from the beginning of the buffer (in bytes) _in window scope_ 1-based offset from the start of the line to the cursor position in Unicode codepoints, which may differ from visible columns if the document contains full-width codepoints (which occupy two columns) or zero-width codepoints _in window scope_ 1-based offset from the start of the line to the cursor position in display column, taking into account tabs and character width. _in window scope_ unicode value of the codepoint under the main cursor _in window scope_ 1-based offset from the start of the line to the first byte of the character under the main cursor (in bytes), the fourth component of `%val{selection_desc}` _in window scope_ line of the main cursor, the third component of `%val{selection_desc}` _in buffer, window scope_ history id of the current buffer, an integer value which refers to a specific buffer version in the undo tree (see also `%val{timestamp}`) _in `hook` command \ parameter_ text captured by capture group _n_, if the executing hook’s filter regex used capture groups _in `hook` command \ parameter_ the complete parameter string of the executing hook _in buffer, window scope_ `true` if the buffer has modifications not saved, otherwise `false` _for commands executed from the object menu’s `` only_ a pipe-separted list of words including `inner` if the user wants an inner selection, `to_begin` if the user wants to select to the beginning, and `to_end` if the user wants to select to the end _in `map` command \ parameter and `` from the object menu_ current register when the mapping was triggered directory containing the kak support files, determined from Kakoune’s binary location _for commands executed from the object menu’s `` only_ `replace` if the new selection should replace the existing, `extend` otherwise _in window scope_ content of the main selection _in window scope_ quoted list of the contents of all selections _in window scope_ range of the main selection, represented as `a.b,c.d` where _a_ is the anchor line, _b_ is the number of bytes from the start of the line to the anchor, _c_ is the cursor line (like `%val{cursor_line}`), _d_ is the number of bytes from the start of the line to the cursor (like `%val{cursor_column}`), and all are 1-based decimal integers _in window scope_ unquoted list of the ranges of all selections, in the same format as `%val{selection_desc}` _in window scope_ length (in codepoints) of the main selection _in window scope_ unquoted list of the lengths (in codepoints) of the selections name of the current session _in `.kak` file_ path of the file currently getting executed (through the source command) _in `prompt` command \ parameter_ the text entered by the user in response to the `prompt` command _in buffer, window scope_ timestamp of the current buffer, an integer that increments each time the buffer is modified, including undoing and redoing previous modifications (see also `%val{history_id}`) unquoted list of user modes. version of the current Kakoune server (git hash or release name) _in window scope_ height of the current Kakoune window _in window scope_ width of the current Kakoune window Values in the above list that do not mention a context are available everywhere. A value described as a “quoted list” will follow the rules of Kakoune string quoting (See [`:doc command-parsing`](https://discuss.kakoune.com/t/command-parsing/537/2)). An “unquoted list” cannot contain any special characters that would require quoting.