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.. _cmd-alias:
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alias - create a function
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=========================
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Synopsis
--------
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docs synopsis: add HTML highlighing and automate manpage markup
Recent synopsis changes move from literal code blocks to
[RST line blocks]. This does not translate well to HTML: it's not
rendered in monospace, so aligment is lost. Additionally, we don't
get syntax highlighting in HTML, which adds differences to our code
samples which are highlighted.
We hard-wrap synopsis lines (like code blocks). To align continuation
lines in manpages we need [backslashes in weird places]. Combined with
the **, *, and `` markup, it's a bit hard to get the alignment right.
Fix these by moving synopsis sources back to code blocks and compute
HTML syntax highlighting and manpage markup with a custom Sphinx
extension.
The new Pygments lexer can tokenize a synopsis and assign the various
highlighting roles, which closely matches fish's syntax highlighing:
- command/keyword (dark blue)
- parameter (light blue)
- operator like and/or/not/&&/|| (cyan)
- grammar metacharacter (black)
For manpage output, we don't project the fish syntax highlighting
but follow the markup convention in GNU's man(1):
bold text type exactly as shown.
italic text replace with appropriate argument.
To make it easy to separate these two automatically, formalize that
(italic) placeholders must be uppercase; while all lowercase text is
interpreted literally (so rendered bold).
This makes manpages more consistent, see string-join(1) and and(1).
Implementation notes:
Since we want manpage formatting but Sphinx's Pygments highlighing
plugin does not support manpage output, add our custom "synopsis"
directive. This directive parses differently when manpage output is
specified. This means that the HTML and manpage build processes must
not share a cache, because the parsed doctrees are cached. Work around
this by using separate cache locations for build targets "sphinx-docs"
(which creates HTML) and "sphinx-manpages". A better solution would
be to only override Sphinx's ManualPageBuilder but that would take a
bit more code (ideally we could override ManualPageWriter but Sphinx
4.3.2 doesn't really support that).
---
Alternative solution: stick with line blocks but use roles like
:command: or :option: (or custom ones). While this would make it
possible to produce HTML that is consistent with code blocks (by adding
a bit of CSS), the source would look uglier and is harder to maintain.
(Let's say we want to add custom formatting to the [|] metacharacters
in HTML. This is much easier with the proposed patch.)
---
[RST line blocks]: https://docutils.sourceforge.io/docs/ref/rst/restructuredtext.html#line-blocks
[backslashes in weird places]: https://github.com/fish-shell/fish-shell/pull/8626#discussion_r782837750
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.. synopsis ::
alias
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alias [--save] NAME DEFINITION
alias [--save] NAME=DEFINITION
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Description
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-----------
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`` alias `` is a simple wrapper for the `` function `` builtin, which creates a function wrapping a command. It has similar syntax to POSIX shell `` alias `` . For other uses, it is recommended to define a :ref: `function <cmd-function>` .
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`` fish `` marks functions that have been created by `` alias `` by including the command used to create them in the function description. You can list `` alias `` -created functions by running `` alias `` without arguments. They must be erased using `` functions -e `` .
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- `` NAME `` is the name of the alias
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- `` DEFINITION `` is the actual command to execute. `` alias `` automatically appends `` $argv `` , so that all parameters used with the alias are passed to the actual command.
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You cannot create an alias to a function with the same name. Note that spaces need to be escaped in the call to `` alias `` just like at the command line, *even inside quoted parts* .
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The following options are available:
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**-h** or **--help**
Displays help about using this command.
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**-s** or **--save**
Saves the function created by the alias into your fish configuration directory using :ref: `funcsave <cmd-funcsave>` .
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Example
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-------
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The following code will create `` rmi `` , which runs `` rm `` with additional arguments on every invocation.
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::
alias rmi="rm -i"
# This is equivalent to entering the following function:
function rmi --wraps rm --description 'alias rmi=rm -i'
rm -i $argv
end
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# This needs to have the spaces escaped or "Chrome.app..."
# will be seen as an argument to "/Applications/Google":
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alias chrome='/Applications/Google\ Chrome.app/Contents/MacOS/Google\ Chrome banana'
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See more
--------
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1. The :ref: `function <cmd-function>` command this builds on.
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2. :ref: `Functions <syntax-function>` .
3. :ref: `Function wrappers <syntax-function-wrappers>` .