How to run a shell function with execute or become

[rbhanot4739]

Lets say we have a shell function defined which can be do different things depending on the arguments passed to it. How can run this function by binding a key with become or execute action ? Here is the example code

greet(){
echo "Hello $@"
}

ls | fzf --bind '<some-key>:become(greet {})

Unfortunately the above does not seem to work key press fails with command greet not found. I have also tried exporting the function but with no success.
One workaround is to simply run the command directly inside the become like become(echo "Hello " {} which works but then if I have logic that I want to reuse across multiple bindings, I would have to repeat the same code.

Another way is to put this function into its own script and then invoke that script, which works, but moving these functions into their own scripts can be painful and overkill if I am working on something more involved .

Am I missing something obvious here, I have searched through docs, example sections, advanced section but could not find anything.

[LangLangBart]

This will depend on your shell. If you are using bash, try it with export -f. As a good measure, assign the SHELL variable to your bash executable, Alternatively, there is also the --with-shell flag.

greet(){
echo "Hello $@"
}
export -f greet
ls | SHELL=$(which bash) fzf --bind '<some-key>:become(greet {})

---

I have also tried exporting the function but with no success.

If you are using zsh, there is no export -f. See this discussion for workarounds: #3993

---

The key lesson to take away is that fzf executes these functions in a child process like this:

Note

fzf runs the command with $SHELL -c if SHELL is set, otherwise with sh -c

[rbhanot4739]

@LangLangBart Yes, I am using zsh. I had considered squishing the function into a single command string but that can become really hard to read and debug. For shorter and one liner functions this approach would work just fine however for longer and complicated functions its non-trivial and I think maybe .zshenv is the way but as you mentioned that has another side effect of very loose code locality !

Is it possible to run the zsh function inside a bash subshell when fzf executes it ? I tried running the following from zshell but it din't work

greet(){
echo "Hello $@"
}
export -f greet
ls | SHELL=$(which bash) fzf --bind '<some-key>:become(greet {})

[LangLangBart]

Within a zsh environment, you can't run export -f greet; it will throw an error.

In a bash environment, like in a script, it will work.

#!/usr/bin/env bash
greet(){
echo "Hello $@"
}
export -f greet
ls | SHELL=$(which bash) fzf --bind '<some-key>:become(greet {})

---

Alternatively, source the function from a specific file and then run it.

# file: ~/greet.zsh
greet(){
echo "Hello $@"
}

# command line
ls | fzf --bind '<some-key>:become(source ~/greet.zsh; greet {})

---

There is also autoload, but this would also require you to write the function in its own file

man zshmisc | less --pattern "AUTOLOADING FUNCTIONS"

This is just an example of using the is-at-least¹ function that comes with every zsh version. Use autoload to call it and test if your fzf version is at least 0.40.1. This is just a demo to illustrate the point.

• is-at-least check if a given command version meets the requirements

autoload -Uz is-at-least
is-at-least 0.40.1 $(fzf --version) && echo YES || echo NO 

There are several useful functions available with every zsh version. You can find them in the share/zsh/functions directory of your zsh distribution, along with many other completion functions. zsh even includes a tetris game, which might not be very helpful, but is amusing.

man zshcontrib | less --pattern tetris

echo "Play Tetris" | SHELL="$(which zsh)" fzf --bind 'enter:become:autoload -Uz tetriscurses; tetriscurses'

Footnotes

1. zsh/code Functions/Misc/is-at-least ↩

[rbhanot4739]

This seems to be the most convenient way if I put this inside a script like test.sh.

#!/usr/bin/env bash
greet(){
echo "Hello $@"
}
export -f greet
ls | SHELL=$(which bash) fzf --bind '<some-key>:become(greet {})

But it still does not work if I run this script like bash test.sh.

Even with autoloading the function fzf somehow fails to correctly load the function, here is the snippet from .zshrc

fpath=(~/zsh_functions $fpath);
autoload -U $fpath[1]/*(.:t)

Now if I open a new shell and run greet Foo I get Hello Foo, but if I do

❯ ls |SHELL="$(which zsh)" fzf --bind 'enter:become(greet)'
zsh:1: command not found: greet

Even with explicit autoloading it isn't working.

❯ ls |SHELL="$(which zsh)" fzf --bind 'enter:become:autoload -Uz greet; greet'
zsh:1: greet: function definition file not found

Here is the functions directory and file named greet inside it.

zsh_functions
└── greet

[LangLangBart]

But it still does not work if I run this script like bash test.sh.

Unable to reproduce the issue. Tried it with the following.

cat <<'EOF' >/tmp/test.sh
#!/usr/bin/env bash
greet(){
echo "Hello $@"
}
export -f greet
ls | SHELL=$(which bash) fzf --bind 'enter:become(greet {})'
EOF

bash /tmp/test.sh

Could you enable xtrace ?

bash -x /tmp/test.sh

---

Even with explicit autoloading it isn't working.

Did you restart your shell before running the command to ensure that the FPATH variable was properly exported? Check the output when printing the listed paths in fpath.

: | SHELL="$(which zsh)" fzf --bind 'start:become: echo "$FPATH"'

or try

fpath=(~/zsh_functions $fpath)
export FPATH=$FPATH

Testing it in a clean environment:

command env -i HOME=$HOME TERM=$TERM USER=$USER PATH=$PATH zsh -f
cd ~
mkdir zsh_functions

cat <<'EOF' > zsh_functions/greet
echo "Hello $@"
EOF

fpath=(~/zsh_functions $fpath)
export FPATH=$FPATH

ls | SHELL="$(which zsh)" fzf --bind 'enter:become:autoload -Uz greet; greet {}'
Hello ...

[rbhanot4739]

@LangLangBart I did some more testing with bash script method and noticed something really strange, the script works outside of tmux but not within tmux. Here is the example

❯ cat  /tmp/test.sh
#!/usr/bin/env bash
greet() {
  echo "Hello $@"
}
export -f greet
ls | SHELL=$(which bash) fzf --bind 'enter:become(greet {})'

❯ FZF_DEFAULT_OPTS=""
❯ bash /tmp/test.sh
Hello catpuccin.txt

Now if I add the --tmux option to default opts, it breaks

❯ cat /tmp/test.sh
#!/usr/bin/env bash
greet() {
  echo "Hello $@"
}
export -f greet
ls | SHELL=$(which bash) fzf --bind 'enter:become(greet {})'

❯ FZF_DEFAULT_OPTS="--tmux"
❯ bash /tmp/test.sh
/opt/homebrew/bin/bash: line 1: greet: command not found

Not sure what's going on here.

[LangLangBart]

the script works outside of tmux but not within tmux

See #4001 (comment)

[rbhanot4739]

@LangLangBart Sorry for stretching this, but I noticed another issue.

tmux ls -F '#{session_name}' | fzf --bind 'enter:become(tmux attach -t {})'
open terminal failed: can't use /dev/tty

It only happens when the command is run as fzf action, if I do tmux attach -t $selection directly after selection=$(tmux ls -F '#{session_name}' | fzf) the session is attached because I guess the command runs in an interactive shell where there is a tty available. I tried passing explicitly as well

tmux ls -F '#{session_name}' | SHELL=`which bash` fzf --bind 'enter:become(tmux attach -t {})'
open terminal failed: can't use /dev/tty

I assume this to be a known behavior but could not find any discussion/issues related to this.

Also did you try running below from within a tmux session ? For me, it works outside of tmux but not from within tmux ? Not sure if I am missing something here but running above from within tmux throws the same command greet not found.

Unable to reproduce the issue. Tried it with the following:.

cat <<'EOF' >/tmp/test.sh
#!/usr/bin/env bash
greet(){
echo "Hello $@"
}
export -f greet
ls | SHELL=$(which bash) fzf --bind 'enter:become(greet {})'
EOF

bash /tmp/test.sh

Could you enable xtrace ?

bash -x /tmp/test.sh

[LangLangBart]

tmux ls -F '#{session_name}' | fzf --bind 'enter:become:tmux attach -t {}'
open terminal failed: can't use /dev/tty

Have you tried the suggestions in the wiki¹ instead ?

---

For me, it works outside of tmux but not from within tmux ?

Running it with --no-tmux should work, both inside and outside of tmux.

ls | SHELL=$(which bash) fzf --no-tmux --bind 'enter:become(greet {})'

If you want to use the --tmux flag, you will need to use the current development version. See commit 4161403.

See BUILD.md² for instructions if you would like to test it, and thank the maintainer for fixing it.

Footnotes

1. Examples tmux · junegunn/fzf Wiki · GitHub ↩

2. fzf/BUILD.md at master · junegunn/fzf · GitHub ↩

[rbhanot4739]

Have you tried the suggestions in the wiki1 instead ?

This regular attach-sssion works just fine, as I mentioned that if I get the selection from fzf like below it works fine.

selection=$(tmux ls -F '#{session_name}' | fzf)
tmux attach-session -t $selection

But when I do tmux ls -F '#{session_name}' | fzf --bind 'enter:become(tmux attach -t {})' it doesn't. Infact if I bound a function to key with --bind which internally calls tmux attach-session it still fails with the same error open terminal failed: can't use /dev/tty.

[LangLangBart]

open terminal failed: can't use /dev/tty

The error message sits in tmux¹² and is triggered by this line:

if (strcmp(c->ttyname, ttynam) == 0)

ttynam derives its value from _PATH_TTY³ (if not otherwise defined it is /dev/tty)
c->ttyname gets its value from ttyname(STDIN_FILENO)⁴

Checking the names of the file descriptors (stdin, stdout, stderr) through fzf's become action.

fzf --bind 'start:become:lsof -p $$ -a -d 0-2'
# COMMAND  PID  USER   FD   TYPE DEVICE SIZE/OFF NODE NAME
# lsof    1584 paria    0r   CHR    2,0      0t0  315 /dev/tty
# lsof    1584 paria    1u   CHR  16,44  0t13551 1297 /dev/ttys044
# lsof    1584 paria    2u   CHR  16,44  0t13551 1297 /dev/ttys044

# or using the `JXA-ObjC Bridge` (macOS)
fzf --with-shell 'osascript -l JavaScript -e' \
  --bind 'start:become:ObjC.import("unistd"); [$.ttyname($.STDIN_FILENO), $.ttyname($.STDOUT_FILENO), $.ttyname($.STDERR_FILENO)].join("\n")'
# /dev/tty
# /dev/ttys044
# /dev/ttys044

If we now require stdin to point to the same location as stderr or stdout, it might just work⁵.

fzf --bind 'start:become:lsof -p $$ -a -d 0-2 </dev/stderr'
# COMMAND  PID  USER   FD   TYPE DEVICE SIZE/OFF NODE NAME
# lsof    1666 paria    0u   CHR  16,44  0t14946 1297 /dev/ttys044
# lsof    1666 paria    1u   CHR  16,44  0t14946 1297 /dev/ttys044
# lsof    1666 paria    2u   CHR  16,44  0t14946 1297 /dev/ttys044

@junegunn would you approve of that workaround?

tmux ls -F '#{session_name}' | fzf --bind 'enter:become:tmux attach -t {} </dev/stderr'

Footnotes

1. tmux/server-client.c at 826ba515beef76dff7d8865599a19e06ae1c4f6a · tmux/tmux · GitHub ↩

2. tmux/cmd-attach-session.c at 826ba515beef76dff7d8865599a19e06ae1c4f6a · tmux/tmux · GitHub ↩

3. tmux/compat.h at 826ba515beef76dff7d8865599a19e06ae1c4f6a · tmux/tmux · GitHub ↩

4. tmux/client.c at 826ba515beef76dff7d8865599a19e06ae1c4f6a · tmux/tmux · GitHub ↩

5. bash - shell command tmux throws can't use /dev/tty error - Unix & Linux Stack Exchange ↩

[bdjnk]

One straightforward way to retain locality of behavior relies on a conditional switch within one file, either to search or to run the bound function, as demonstrated in this test.sh file.

greet() {
	echo "Hello $@"
}

find() {
	ls | fzf --bind 'h:become(./test.sh greet {})'
}

case $1 in
	greet ) greet $2 ;;
	*     ) find     ;;
esac

The result will be simple to understand and flexible enough to handle complex scenarios as needed.