fzfmenu: DRY and don't create temporary file

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

@@ -29,21 +29,34 @@ in
 
 pkgs.writeDashBin "fzfmenu" ''
   set -efu
+
+  # 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
+    exec 0<&''${FZFMENU_INPUT_FD-0}
+    exec 1>&''${FZFMENU_OUTPUT_FD-1}
+  fi
+
   PROMPT=">"
-  for i in "$@"
+  for i in "$@"; do
-  do
     case $i in
       -p)
-      PROMPT="$2"
+        PROMPT=$2
-      shift
+        shift 2
-      shift
         break
         ;;
       -l)
         # no reason to filter number of lines
-      LINES="$2"
+        LINES=$2
-      shift
+        shift 2
-      shift
         break
         ;;
       -i)
@@ -57,27 +70,12 @@ pkgs.writeDashBin "fzfmenu" ''
         ;;
     esac
   done
-  INPUT=$(${pkgs.coreutils}/bin/cat)
+
-  OUTPUT="$(${pkgs.coreutils}/bin/mktemp)"
+  ${pkgs.fzf}/bin/fzf \
-  if [ -z ''${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 \
-          > \"$OUTPUT\"" 2>/dev/null
-  else
-    echo "$INPUT" | ${pkgs.fzf}/bin/fzf \
       --history=/dev/null \
       --print-query \
       --prompt="$PROMPT" \
       --reverse \
-      > "$OUTPUT"
+    |
-  fi
+  ${pkgs.coreutils}/bin/tail -1
-  ${pkgs.coreutils}/bin/tail -1 "$OUTPUT"
-  ${pkgs.coreutils}/bin/rm "$OUTPUT"
 ''