feat: Add custom shell flag option for command execution

[LangLangBart]

proposal

Ability to alter the flag that is passed to the $SHELL command.

---

For example, if the -c flag could be altered to -e, one could use jsc (JavaScriptCore) to execute JavaScript code without adding jsc -e to every line.

# List available globals in 'jsc' and preview their properties
# 'jsc' only comes by default on macOS
SHELL=/System/Library/Frameworks/JavaScriptCore.framework/Versions/A/Helpers/jsc \
  FZF_SHELL_FLAG="-e" \
  fzf \
  --bind 'start:reload:print(Object.getOwnPropertyNames(globalThis).join("\n"))' \
  --bind 'enter:become:print((![]+[])[+[]]+([][[]]+[])[+[]]+([][[]]+[])[+!![]])' \
  --preview 'const f = globalThis[{}]; if (f) { print(`{} Static Properties\n${Object.getOwnPropertyNames(f).sort().join("\n")}`); if (f.prototype) print(`\n{} Prototype Properties\n${Object.getOwnPropertyNames(f.prototype).sort().join("\n")}`)}'

Another example using bun and --print.

# [bun] https://github.com/oven-sh/bun
# brew install oven-sh/bun/bun
# [gh] https://github.com/cli/cli
# Show starred repos and preview the date of the first commit in a Korean time format
user_name=gh api graphql -f query='{viewer{login}}' --jq '..|.login? // empty'
gh api users/${user_name}/starred \
  --jq '.[] | select(.visibility == "public") | .full_name' |
  SHELL="$(which bun)" FZF_SHELL_FLAG="--print" \
    fzf --prompt "Starred [${user_name}]" \
	--preview '((repo)=>fetch(`https://api.github.com/repos/${repo}/commits?per_page=1`).then((i)=>fetch(i.headers.get("link")?.match(/http[^>]+/g)?.at(-1)).then((t)=>t.json().then((S)=>`First commit: ${repo}\n${new Intl.DateTimeFormat("ko-Kr",{timeStyle:"full",dateStyle:"full"}).format(new Date(S[0].commit.author.date))}`))))({})'

Pro:

• Enables the execution of commands without requiring the flag and command to be prepended on every
  line, which also diminishes the need for one round of quoting.

Con:

• It may lead to confusion and inconsistencies if not used carefully and documented clearly.

---

Issues

• Writing tests
• Windows (not tested at all)
• Better documention

[junegunn]

Thanks, but I'm not sure about this. Correct me if I'm wrong, but we can achieve the same thing by setting $SHELL to a simple wrapper script that handles the flags, which I think is not bad.

fzf2() (
  export SHELL=/tmp/fzfsh
  if ! [[ -x $SHELL ]]; then
    echo '#!/bin/sh' > "$SHELL"
    echo 'shift; echo "$@"' >> "$SHELL"
    chmod +x "$SHELL"
  fi
  command fzf "$@"
)

fzf2 --preview 'run this command: {}'

Having this option may save a few lines of code in some cases, but I'm afraid it will be a niche feature that few will use.

[junegunn]

The Windows situation is a bit messy now, and adding support for this might make it more complicated.

fzf/src/util/util_windows.go

Lines 41 to 63 in e86b81b

	func ExecCommandWith(shell string, command string, setpgid bool) *exec.Cmd {
	var cmd *exec.Cmd
	if strings.Contains(shell, "cmd") {
	cmd = exec.Command(shell)
	cmd.SysProcAttr = &syscall.SysProcAttr{
	HideWindow: false,
	CmdLine: fmt.Sprintf(` /v:on/s/c "%s"`, command),
	CreationFlags: 0,
	}
	return cmd
	}
	if strings.Contains(shell, "pwsh") || strings.Contains(shell, "powershell") {
	cmd = exec.Command(shell, "-NoProfile", "-Command", command)
	} else {
	cmd = exec.Command(shell, "-c", command)
	}
	cmd.SysProcAttr = &syscall.SysProcAttr{
	HideWindow: false,
	CreationFlags: 0,
	}
	return cmd
	}

[LangLangBart]

simple wrapper script that handles the flags

Your wrapper script is a simple and effective solution. No need for a new feature that few would utilize.

[junegunn]

that few would utilize

Technically, this was just my guess, so I can't be 100% sure. But if I recall correctly, there hasn't been a feature request for this in the past years. But if you still like the idea, we can keep this PR open for a while and see what others think.

IMO, if we're really going to add this, it should be easier to use than 1. setting two environment variables, 2. or creating a wrapper script. Something like fzf --with-shell "$SHELL -c" maybe? Hmm, then we would have another problem of splitting the arguments without the help from a shell. (e.g. fzf --with-shell 'custom-shell --title "hello fzf" -c')

[LangLangBart]

I can't reopen the PR as the repo was deleted, but I will file an issue report.