These are the draft release notes for fish 4.0.0. Like this release of fish itself, they are in beta and are not complete. Please report any issues you find.

fish’s core code has been ported from C++ to Rust (#9512).
This means a large change in dependencies and how to build fish.
Packagers should see the For Distributors section at the end.

Notable backwards-incompatible changes

• As part of a larger binding rework, bind gained a new key notation.
  In most cases the old notation should keep working, but in rare cases you may have to change a bind invocation to use the new notation.
  See below for details.

• Terminals that fail to ignore unrecognized OSC or CSI sequences may display garbage. We know cool-retro-term and emacs’ ansi-term are affected,
  most mainstream terminals are not.

• alt-left and alt-right will now move by one argument (which may contain quoted spaces), not just one word like ctrl-left and ctrl-right do.

• alt-backspace will delete an entire argument, not just one word (which is ctrl-backspace now).

• random will produce different values from previous versions of fish when used with the same seed, and will work more sensibly with small seed numbers.
  The seed was never guaranteed to give the same result across systems,
  so we do not expect this to have a large impact (#9593).

• Variables in command position that expand to a subcommand keyword are now forbidden to fix a likely user error.
  For example, set editor command emacs; $editor is no longer allowed (#10249).

• functions --handlers will now list handlers in a different order.
  Now it is definition order, first to last, where before it was last to first.
  This was never specifically defined, and we recommend not relying on a specific order (#9944).

• The qmark-noglob feature, introduced in fish 3.0, is enabled by default. That means ? will no longer act as a single-character glob.
  You can, for the time being, turn it back on by adding no-qmark-noglob to fish_features and restarting fish:

  set -Ua fish_features no-qmark-noglob
  

  The flag will eventually be made read-only, making it impossible to turn off.

• fish no longer searches directories from the Windows system/user $PATH environment variable for Linux executables. To execute Linux binaries by name (i.e. not with a relative or absolute path) from a Windows folder, make sure the /mnt/c/... path is explicitly added to $fish_user_paths and not just automatically appended to $PATH by wsl.exe (#10506).

• Under Microsoft Windows Subsystem for Linux 1 (not WSL 2) , backgrounded jobs that have not been disowned and do not terminate on their own after a SIGHUP + SIGCONT sequence will be explicitly killed by fish on exit (after the usual prompt to close or disown them) to work around a WSL 1 deficiency that sees backgrounded processes that run into SIGTTOU remain in a suspended state indefinitely (#5263). The workaround is to explicitly disown processes you wish to outlive the shell session.

Notable improvements and fixes

• fish now requests XTerm’s modifyOtherKeys keyboard encoding and kitty keyboard protocol’s progressive enhancements (#10359).
  Depending on terminal support, this allows to binding more key combinations, including arbitrary combinations of modifiers ctrl, alt and shift, and distinguishing (for example) ctrl-i from tab.

  Additionally, bind now supports a human-readable syntax in addition to byte sequences.
  This includes modifier names, and names for keys like enter and backspace.
  For example

  • bind up 'do something' binds the up-arrow key instead of a two-key sequence (“u” and then “p”)
  • bind ctrl-x,alt-c 'do something' binds a sequence of two keys.

  Any key argument that starts with an ASCII control character (like e or cX) or is up to 3 characters long, not a named key, and does not contain , or - will be interpreted in the old syntax to keep compatibility for the majority of bindings.

• fish can now be built as a self-installing binary (#10367). That means it can be easily built on one system and copied to another, where it can extract supporting files.
  To do this, run:

  cargo install --path . # in a clone of the fish repository
  # or `cargo build --release` and copy target/release/fish{,_indent,_key_reader} wherever you want
  

  The first time it runs interactively, it will extract all the data files to ~/.local/share/fish/install/. To uninstall, remove the fish binaries and that directory.

  This build system is experimental; the main build system, using cmake, remains the recommended approach for packaging and installation to a prefix.

• A new function fish_should_add_to_history can be overridden to decide whether a command should be added to the history (#10302).

• ctrl-c during command input no longer prints ^C and a new prompt, but merely clears the command line. This restores the behavior from version 2.2. To revert to the old behavior, use bind ctrl-c __fish_cancel_commandline (#10213).

• Bindings can now mix special input functions and shell commands, so bind ctrl-g expand-abbr "commandline -i n" works as expected (#8186).

• Special input functions run from bindings via commandline -f are now applied immediately, instead of after the currently executing binding (#3031).
  For example, commandline -i foo; commandline | grep foo succeeds now.

• Undo history is no longer truncated after every command, but kept for the lifetime of the shell process.

• The ctrl-r history search now uses glob syntax (#10131).

• The ctrl-r history search now operates only on the line or command substitution at cursor, making it easier to combine commands from history.

• Abbreviations can now be restricted to specific commands. For instance:

  abbr --add --command git back 'reset --hard HEAD^'
  

  will expand “back” to reset --hard HEAD^, but only when the command is git (#9411).

Deprecations and removed features

• commandline --tokenize (short option -o) has been deprecated in favor of commandline --tokens-expanded (short option -x) which expands variables and other shell syntax, removing the need to use eval in completion scripts (#10212).

• Two new feature flags:

  • remove-percent-self (see status features) disables PID expansion of %self, which has been supplanted by $fish_pid (#10262).
  • test-require-arg disables test’s one-argument mode. That means test -n without an additional argument will return false, test -z will keep returning true. Any other option without an argument, anything that is not an option and no argument will be an error. This also goes for [, test’s alternate name.
    This is a frequent source of confusion and so we are breaking with POSIX explicitly in this regard.
    In addition to the feature flag, there is a debug category “deprecated-test”. Running fish with fish -d deprecated-test will show warnings whenever a test invocation that would change is used. (#10365).

  These can be enabled with:

  set -Ua fish_features remove-percent-self test-require-arg
  

  We intend to enable them by default in future, and after that eventually make them read-only.

• Specifying key names as terminfo names (using the bind -k syntax) is deprecated and may be removed in a future version.

• When a terminal pastes text into fish using bracketed paste, fish used to switch to a special paste bind mode.
  This bind mode has been removed. The behavior on paste is no longer configurable.

• When an interactive fish is stopped or terminated by a signal that cannot be caught (SIGSTOP or SIGKILL), it may leave the terminal in a state where keypresses with modifiers are sent as CSI u sequences, instead of traditional control characters or escape sequences that are recognized by Readline and compatible programs, such as bash and python.
  If this happens, you can use the reset command from ncurses to restore the terminal state.

• fish_key_reader --verbose no longer shows timing information.

• Terminal information is no longer read from hashed terminfo databases, or termcap databases (#10269). The vast majority of systems use a non-hashed terminfo database, which is still supported.

Scripting improvements

• for loops will no longer remember local variables from the previous iteration (#10525).
• A new history append subcommand appends a command to the history, without executing it (#4506).
• A new redirection: will try opening the file as input, and if it doesn’t succeed silently uses /dev/null instead.
This can help with checks like test -f /path/to/file; and string replace foo bar < /path/to/file. (#10387)
• A new option commandline --tokens-raw prints a list of tokens without any unescaping (#10212).
• A new option commandline --showing-suggestion tests whether an autosuggestion is currently displayed (#10586).
• functions and type now show that a function was copied and its source, rather than solely Defined interactively (#6575).
• Stack trace now shows line numbers for copied functions (#6575).
• foo & && bar is now a syntax error, like in other shells (#9911).
• if -e foo; end now prints a more accurate error (#10000).
• cd into a directory that is not readable but accessible (permissions --x) is now possible (#10432).
• An integer overflow in string repeat leading to a near-infinite loop has been fixed (#9899).
• string shorten behaves better in the presence of non-printable characters, including fixing an integer overflow that shortened strings more than intended (#9854).
• string pad no longer allows non-printable characters as padding (#9854).
• string repeat now allows omission of -n when the first argument is an integer (#10282).
• string match and replace have a new --max-matches option to return as soon as the specified number of matches have been identified, which can improve performance in scripts (#10587).
• functions --handlers-type caller-exit once again lists functions defined as function --on-job-exit caller, rather than them being listed by functions --handlers-type process-exit.
• A new set --no-event option sets or erases variables without triggering a variable event. This can be useful to change a variable in an event handler (#10480).
• Commas in command substitution output are no longer used as separators in brace expansion, preventing a surprising expansion in some cases (#5048).
• Universal variables can now store strings containing invalid UTF-8 (#10313).
• A new path basename -E option that causes it to return the basename (“filename” with the directory prefix removed) with the final extension (if any) also removed. This is a shorter version of path change-extension "" (path basename $foo) (#10521).
• A new math --scale-mode option to select truncate, round, floor, ceiling as you wish; the default value is truncate. (#9117).
• random is now less strict about its arguments, allowing a start larger or equal to the end. (#10879)