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152 lines
4.8 KiB
Plaintext
152 lines
4.8 KiB
Plaintext
Writing kak scripts
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===================
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Interaction with external tools from a Kakoune session is supported
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through the use of scripts. Once loaded by the editor (either
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automatically or manually), they allow extending the functionalities
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provided by default through commands and hooks.
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Their implementation should be kept as simple as possible, as they are
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not meant to be generic tools themselves but a mere API to actual
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software.
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---------------------------------------------------
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+------+
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+--> | tmux |
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| +------+
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+---------+ | +------+
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| Kakoune | <-------> scripts +-+--> | X11 |
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+---------+ | +------+
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| +------+
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+--> | ... |
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+------+
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---------------------------------------------------
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Dependencies
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------------
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The amount of dependencies of a given script should be kept to a minimum
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for practicality reasons, and have to be reasonable and expected
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considering the purpose of the script itself.
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Examples:
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* the `clang.kak` script provides with code completion using the `clang`
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compiler
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* the `tmux.kak` script provides with terminal splitting using the
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`tmux` multiplexer
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* the `ctags.kak` script provides with symbol lookups using the
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`readtags` utility provided by some `ctags` implementations
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Naming convention
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-----------------
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All options and commands declared in a Kakoune script have to be
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prefixed with the name of the script, or a one word description of the
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purpose of the script.
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Examples:
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* in `tmux.kak`: command `tmux-new-window`
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* in `comment.kak`: option `comment_line`
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The following conventions apply as well:
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* *options*: if a separator is needed to separate a multiple word option
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name, an underscore should be used to allow shell scopes to use them
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* *commands*: if a separator is needed, a hyphen is usually used to
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differentiate a command name from an option's; this doesn't apply to
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the leading underscore sign in case of a hidden command
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Documentation
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-------------
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Non-hidden commands and options should always be declared with a documentation
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string, so that their purpose is clearly described whenever completed upon
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interactively from the prompt.
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POSIX shell
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-----------
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Shell expansions are a useful tool to interact with an external utility,
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and the shell code that they contain should be as portable as possible. As
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such, scripts that rely on those expansions have to be implemented with
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POSIX in mind, most shells follow this standard nowadays which somewhat
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guarantees that the script will be portable across the most common systems.
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Common shell patterns
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---------------------
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Printing variables
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~~~~~~~~~~~~~~~~~~
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In order to print a string that contains a variable expansion, prefer
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`printf` to `echo`, as the latter is implementation defined and may
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interpret some characters differently depending on the shell (e.g.
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flags, backslashes).
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----------------------------------
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printf %s\\n "${var}"
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printf "value: %s\\n" "${var}"
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----------------------------------
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The following won't cause any issues, as the string to print doesn't
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contain ambiguous characters:
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-------------------------------------
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echo "set global scrolloff 999,0"
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-------------------------------------
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Variable base name
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~~~~~~~~~~~~~~~~~~
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Replace `$(basename "${var}")` with `"${var##*/}"`.
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Testing
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~~~~~~~
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The `[[` keyword is provided by `bash`, and should be replaced with `[`.
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Standard error redirection
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~~~~~~~~~~~~~~~~~~~~~~~~~~
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Redirecting both standard and error streams is simplified in the `bash`
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shell with the `&>` operator, however this syntax is not portable and
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has to be replaced with the following: `>/dev/null 2>&1`.
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Regular expression
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~~~~~~~~~~~~~~~~~~
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The `bash` shell provides with a `[[` keyword that supports the `=~`
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operator to match a regular expression against a variable. This
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functionality can be implemented with the `expr` utility:
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* `expr "${var}" : '[a-z]*' >/dev/null` returns successfully when the
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variable is empty or only contains lowercase characters, otherwise a
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non-zero exit code is returned
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* `expr "${var}" : '\([a-z]*\)'` prints the variable when empty or
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only contains lowercase characters
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Note that the regular expression matches the whole string, using the `^`
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and `$` anchors is an undefined behavior.
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Running a process in the background
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~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
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In order to get a process running in the background without having it
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quit when the shell scope that spawns it terminates, use the following
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syntax:
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--------------------------------
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{
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command
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} </dev/null >/dev/null 2>&1 &
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--------------------------------
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