fzfmenu: DRY and don't create temporary file

krebs/5pkgs/simple/fzfmenu/default.nix

@@ -29,55 +29,53 @@ in
 
 pkgs.writeDashBin "fzfmenu" ''
   set -efu
-  PROMPT=">"
-  for i in "$@"
-  do
-  case $i in
-      -p)
-      PROMPT="$2"
-      shift
-      shift
-      break
-      ;;
-      -l)
-      # no reason to filter number of lines
-      LINES="$2"
-      shift
-      shift
-      break
-      ;;
-      -i)
-      # we do this anyway
-      shift
-      break
-      ;;
-      *)
-      echo "Unknown option $1" >&2
-      shift
-      ;;
-  esac
-  done
-  INPUT=$(${pkgs.coreutils}/bin/cat)
-  OUTPUT="$(${pkgs.coreutils}/bin/mktemp)"
-  if [ -z ''${TERM+x} ]; then #check if we can print fzf in the shell
-    ${pkgs.rxvt_unicode}/bin/urxvt \
-      -name ${cfg.appName} \
-      -title ${shell.escape cfg.windowTitle} \
-      -e ${pkgs.dash}/bin/dash -c \
-        "echo \"$INPUT\" | ${pkgs.fzf}/bin/fzf \
-          --history=/dev/null \
-          --print-query \
-          --prompt=\"$PROMPT\" \
-          --reverse \
-          > \"$OUTPUT\"" 2>/dev/null
+
+  # Spawn terminal if called without one, like e.g. from a window manager.
+  if [ -z ''${TERM+x} ]; then
+    exec 3<&0
+    exec 4>&1
+    export FZFMENU_INPUT_FD=3
+    export FZFMENU_OUTPUT_FD=4
+    exec ${pkgs.rxvt_unicode}/bin/urxvt \
+        -name ${cfg.appName} \
+        -title ${shell.escape cfg.windowTitle} \
+        -e "$0" "$@"
   else
-    echo "$INPUT" | ${pkgs.fzf}/bin/fzf \
+    exec 0<&''${FZFMENU_INPUT_FD-0}
+    exec 1>&''${FZFMENU_OUTPUT_FD-1}
+  fi
+
+  PROMPT=">"
+  for i in "$@"; do
+    case $i in
+      -p)
+        PROMPT=$2
+        shift 2
+        break
+        ;;
+      -l)
+        # no reason to filter number of lines
+        LINES=$2
+        shift 2
+        break
+        ;;
+      -i)
+        # we do this anyway
+        shift
+        break
+        ;;
+      *)
+        echo "Unknown option $1" >&2
+        shift
+        ;;
+    esac
+  done
+
+  ${pkgs.fzf}/bin/fzf \
       --history=/dev/null \
       --print-query \
       --prompt="$PROMPT" \
       --reverse \
-      > "$OUTPUT"
-  fi
-  ${pkgs.coreutils}/bin/tail -1 "$OUTPUT"
-  ${pkgs.coreutils}/bin/rm "$OUTPUT"
+    |
+  ${pkgs.coreutils}/bin/tail -1
 ''