Fix fzf preview under non-POSIX login shells (e.g. fish)

[johnstegeman]

Problem

With a non-POSIX login shell (e.g. fish), the fzf preview pane fails immediately:

fish: Unsupported use of '='. In fish, please use 'set pathname '/path/to/dir''.
pathname='/path/to/dir/'; LC_ALL=C ls -AC --color=always "$pathname"

Cause

_ze_find and _ze_dig build the fzf --preview command in POSIX shell syntax (pathname={2..}; ...). fzf executes preview commands with $SHELL -c (fzf docs: "the default value is $SHELL -c if $SHELL is set, otherwise sh -c"). When $SHELL is fish, fish cannot parse a bare VAR=value assignment, so the preview dies before the listing runs. The preview is spawned by fzf itself, so running ze.sh's logic under bash (as the fish wrapper does) does not help.

Fix

Reworked per @jghub's feedback — two independent changes:

1. Interpolate the placeholder directly ({2..}) instead of first assigning it to a shell variable. fzf already single-quotes placeholder expansions (this is the same quoting the old pathname={2..} relied on), so the result is equivalent, but the preview command no longer contains any shell-specific assignment syntax. This keeps it working on any shell and on fzf versions older than 0.48 (Debian bookworm ships 0.38, Ubuntu 24.04 ships 0.44.1), where --with-shell does not exist.

2. Pin SHELL=/bin/sh on both fzf calls, so the preview is always spawned by a POSIX shell regardless of the user's login shell. This also prevents the interactive shell's functions/aliases from leaking into the preview — e.g. a fish ls function wrapping eza, which rejects -C and would otherwise break the preview even after the parse error is gone. It also future-proofs other wrappers (nushell, …).

-    typeset metric header mode=${3:-dirs} preview='pathname={2..}'
+    typeset metric header mode=${3:-dirs}
 ...
-        files) preview+='; head -256 -- "$pathname"'; zopts+=(-o);;
-        *)     preview+='; LC_ALL=C ls -AC --color=always "$pathname"';;
+        files) preview='head -256 -- {2..}'; zopts+=(-o);;
+        *)     preview='LC_ALL=C ls -AC --color=always {2..}';;
 ...
-            … | fzf "${fzfopts[@]}" | cut -f2-)
+            … | SHELL=/bin/sh fzf "${fzfopts[@]}" | cut -f2-)

(and the analogous edits in _ze_dig). The --with-shell approach from the first revision is dropped, since pinning SHELL covers it without the fzf >= 0.48 requirement.

Verification

• bash -n / zsh -n / ksh -n: OK
• fzf driven in a pty with the login shell set to fish and a path containing a space and a single quote: preview runs under /bin/sh and lists the directory correctly ({2..} quoting intact).
• End-to-end fish -c 'ze -f iris' and fish -c 'ze -d': no Unsupported use of '=' and no eza -C errors.
• Non-fzf fallbacks (_ZE_NO_FZF) unaffected.

[jghub]

Thanks for tracking this down. I am not an active fish user (and I did not think of the fish-as-login-shell scenario), so the report is appreciated.

Direct {2..} interpolation is a good fix and I'll merge it once you've updated the PR. I think that it is principally preferable to keep the preview command free of shell-specific assignment syntax. E.g. debian/ubuntu still ships fzf 0.44 AFAIK so the --with-shell fix would not suffice for those OSes.

Separately/alternatively, I'd still like to pin /bin/sh for the fzf call, since a future wrapper (nushell, for example) could hit the same problem (this also should resolve the environment leakage issue you mention). Proposed change:

--- a/ze.sh
+++ b/ze.sh
@@ -189,7 +189,7 @@
         header="${mode%s} stack ranked by $metric"
         fzfopts=( -0 -e --no-sort --preview-window='top,19%' --header="$header" --color='header:bright-red' --preview "$preview" )
         (set -o pipefail; _ze "${zopts[@]}" -- "$1" | cut -f2- |
-            awk '{ buf[NR] = $0 } END { offs = NR+1; while (NR) print offs-NR "\t" buf[NR--] }' | fzf "${fzfopts[@]}" | cut -f2-)
+            awk '{ buf[NR] = $0 } END { offs = NR+1; while (NR) print offs-NR "\t" buf[NR--] }' | SHELL=/bin/sh fzf "${fzfopts[@]}" | cut -f2-)
     fi
 }

I tested it in fish with

begin; set -lx SHELL (command -v fish); ze -f; end

so that ze.sh then sees SHELL as fish on startup. so this approach also woul fix the issue (but your 'direct interpolation' variant still should be adopted in the first place).

[jghub]

'preview' still needs to be declared to keep it local to the respective function.