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docs: Some more on tutorial and combiners

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Fabian Boehm 2022-12-27 14:17:27 +01:00
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22
doc_src/language.rst
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@ -408,6 +408,28 @@ Some examples::
set -q XDG_CONFIG_HOME; and set -l configdir $XDG_CONFIG_HOME
or set -l configdir ~/.config
Note that combiners are *lazy* - only the part that is necessary to determine the final status is run.
Compare::
if sleep 2; and false
echo 'How did I get here? This should be impossible'
end
and::
if false; and sleep 2
echo 'How did I get here? This should be impossible'
end
These do essentially the same thing, but the former takes 2 seconds longer because the ``sleep`` always needs to run. So, in cases like these, the ordering is quite important for performance.
Or you can have a case where it is necessary to stop early::
if command -sq foo; and foo
If this went on after seeing that the command "foo" doesn't exist, it would try to run ``foo`` and error because it wasn't found!
For more, see the documentation for the builtins or the :ref:`Conditionals <tut-conditionals>` section of the tutorial.
.. _syntax-loops-and-blocks:

43
doc_src/tutorial.rst
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@ -77,6 +77,7 @@ Run ``help`` to open fish's help in a web browser, and ``man`` with the page (li
set - handle shell variables
Synopsis...
To open this section, use ``help getting-help``.
Syntax Highlighting
-------------------
@ -140,7 +141,7 @@ You can include multiple wildcards::
lesson.pdf
Especially powerful is the recursive wildcard ** which searches directories recursively::
The recursive wildcard ``**`` searches directories recursively::
> ls /var/**.log
/var/log/system.log
@ -159,19 +160,15 @@ You can pipe between commands with the usual vertical bar::
> echo hello world | wc
1 2 12
stdin and stdout can be redirected via the familiar ``<`` and ``>``. stderr is redirected with a ``2>``.
::
> grep fish < /etc/shells > ~/output.txt 2> ~/errors.txt
To redirect stdout and stderr into one file, you can use ``&>``::
To redirect stdout and stderr into one file, you need to first redirect stdout, and then stderr into stdout::
> make > make_output.txt 2>&1
> make &> make_output.txt
For more, see :ref:`Input and output redirections <redirects>` and :ref:`Pipes <pipes>`.
@ -227,10 +224,10 @@ If there's more than one possibility, it will list them:
:class: highlight
:prompt:`>` :red:`~/stuff/s`:kbd:`Tab`
~/stuff/script.sh (Executable, 4.8kB) ~/stuff/sources/ (Directory)
~/stuff/script.sh :gray:`(command)` ~/stuff/sources/ :gray:`(directory)`
Hit tab again to cycle through the possibilities.
Hit tab again to cycle through the possibilities. The part in parentheses there (that "command" and "directory") is the completion description. It's just a short hint to explain what kind of argument it is.
fish can also complete many commands, like git branches:
@ -239,8 +236,7 @@ fish can also complete many commands, like git branches:
:prompt:`>` :command:`git` :param:`merge pr`:kbd:`Tab` => :command:`git` :param:`merge prompt_designer`
:prompt:`>` :command:`git` :param:`checkout b`:kbd:`Tab`
builtin_list_io_merge (Branch) builtin_set_color (Branch) busted_events (Tag)
builtin_list_io_merge :gray:`(Branch)` builtin_set_color :gray:`(Branch)` busted_events :gray:`(Tag)`
Try hitting tab and see what fish can do!
@ -252,7 +248,6 @@ Like other shells, a dollar sign followed by a variable name is replaced with th
> echo My home directory is $HOME
My home directory is /home/tutorial
This is known as variable substitution, and it also happens in double quotes, but not single quotes::
> echo "My current directory is $PWD"
@ -260,8 +255,7 @@ This is known as variable substitution, and it also happens in double quotes, bu
> echo 'My current directory is $PWD'
My current directory is $PWD
Unlike other shells, fish has no dedicated ``VARIABLE=VALUE`` syntax for setting variables. Instead it has an ordinary command: ``set``, which takes a variable name, and then its value.
Unlike other shells, fish has an ordinary command to set variables: ``set``, which takes a variable name, and then its value.
::
@ -278,7 +272,6 @@ Unlike other shells, variables are not further split after substitution::
> ls
Mister Noodle
In bash, this would have created two directories "Mister" and "Noodle". In fish, it created only one: the variable had the value "Mister Noodle", so that is the argument that was passed to ``mkdir``, spaces and all.
You can erase (or "delete") a variable with ``-e`` or ``--erase``
@ -298,7 +291,7 @@ Exports (Shell Variables)
Sometimes you need to have a variable available to an external command, often as a setting. For example many programs like ``git`` or ``man`` read the ``$PAGER`` variable to figure out your preferred pager (the program that lets you scroll text). Other variables used like this include ``$BROWSER``, ``$LANG`` (to configure your language) and ``$PATH``. You'll note these are written in ALLCAPS, but that's just a convention.
To give a variable to an external command, it needs to be "exported". Unlike other shells, fish does not have an export command. Instead, a variable is exported via an option to ``set``, either ``--export`` or just ``-x``.
To give a variable to an external command, it needs to be "exported". This is done with a flag to ``set``, either ``--export`` or just ``-x``.
::
@ -407,7 +400,7 @@ Command substitutions without a dollar are not expanded within quotes, so the ve
> ls *.txt
testing_1360099791.txt
Unlike other shells, fish does not split command substitutions on any whitespace (like spaces or tabs), only newlines. This can be an issue with commands like ``pkg-config`` that print what is meant to be multiple arguments on a single line. To split it on spaces too, use ``string split``.
Unlike other shells, fish does not split command substitutions on any whitespace (like spaces or tabs), only newlines. Usually this is a big help because unix commands operate on a line-by-line basis. Sometimes it can be an issue with commands like ``pkg-config`` that print what is meant to be multiple arguments on a single line. To split it on spaces too, use ``string split``.
::
@ -444,15 +437,15 @@ To write them on the same line, use the semicolon (";"). That means the followin
echo fish
echo chips
This is useful interactively to enter multiple commands. In a script it's easier to read if the commands are on separate lines.
Exit Status
-----------
When a command exits, it returns a status code as a non-negative integer.
When a command exits, it returns a status code as a non-negative integer (that's a whole number >= 0).
Unlike other shells, fish stores the exit status of the last command in ``$status`` instead of ``$?``.
::
> false
@ -497,7 +490,6 @@ Conditionals (If, Else, Switch)
Use :doc:`if <cmds/if>` and :doc:`else <cmds/else>` to conditionally execute code, based on the exit status of a command.
::
if grep fish /etc/shells
@ -508,10 +500,8 @@ Use :doc:`if <cmds/if>` and :doc:`else <cmds/else>` to conditionally execute cod
echo Got nothing
end
To compare strings or numbers or check file properties (whether a file exists or is writeable and such), use :doc:`test <cmds/test>`, like
::
if test "$fish" = "flounder"
@ -538,14 +528,12 @@ To compare strings or numbers or check file properties (whether a file exists or
:ref:`Combiners <tut-combiners>` can also be used to make more complex conditions, like
::
if grep fish /etc/shells; and command -sq fish
if command -sq fish; and grep fish /etc/shells
echo fish is installed and configured
end
For even more complex conditions, use :doc:`begin <cmds/begin>` and :doc:`end <cmds/end>` to group parts of them.
There is also a :doc:`switch <cmds/switch>` command::
@ -578,7 +566,6 @@ A fish function is a list of commands, which may optionally take arguments. Unli
say_hello everybody!
# prints: Hello everybody!
Unlike other shells, fish does not have aliases or special prompt syntax. Functions take their place. [#]_
You can list the names of all functions with the :doc:`functions <cmds/functions>` builtin (note the plural!). fish starts out with a number of functions::
@ -586,8 +573,6 @@ You can list the names of all functions with the :doc:`functions <cmds/functions
> functions
N_, abbr, alias, bg, cd, cdh, contains_seq, dirh, dirs, disown, down-or-search, edit_command_buffer, export, fg, fish_add_path, fish_breakpoint_prompt, fish_clipboard_copy, fish_clipboard_paste, fish_config, fish_default_key_bindings, fish_default_mode_prompt, fish_git_prompt, fish_hg_prompt, fish_hybrid_key_bindings, fish_indent, fish_is_root_user, fish_job_summary, fish_key_reader, fish_md5, fish_mode_prompt, fish_npm_helper, fish_opt, fish_print_git_action, fish_print_hg_root, fish_prompt, fish_sigtrap_handler, fish_svn_prompt, fish_title, fish_update_completions, fish_vcs_prompt, fish_vi_cursor, fish_vi_key_bindings, funced, funcsave, grep, help, history, hostname, isatty, kill, la, ll, ls, man, nextd, open, popd, prevd, prompt_hostname, prompt_pwd, psub, pushd, realpath, seq, setenv, suspend, trap, type, umask, up-or-search, vared, wait
You can see the source for any function by passing its name to ``functions``::
> functions ls
@ -613,14 +598,12 @@ While loops::
# Loop forever
# yes, this really will loop forever. Unless you abort it with ctrl-c.
For loops can be used to iterate over a list. For example, a list of files::
for file in *.txt
cp $file $file.bak
end
Iterating over a list of numbers can be done with ``seq``::
for x in (seq 5)