slack-cli: fix dirname hack

pkgs/tools/networking/slack-cli/default.nix

@@ -7,20 +7,7 @@
 
 { stdenv, lib, writeShellScriptBin, fetchFromGitHub, curl, jq }:
 
-let
+stdenv.mkDerivation rec {
-  wrapper = writeShellScriptBin "slack" ''
-    [ "$1" = "init" -a -z "$SLACK_CLI_TOKEN" ] && cat >&2 <<-'MESSAGE'
-    WARNING: slack-cli must be configured using the SLACK_CLI_TOKEN environment
-    variable. Using `slack init` will not work because it tries to write to the
-    Nix store.
-
-    MESSAGE
-
-    export PATH=${lib.makeBinPath [ curl jq ]}:"$PATH"
-    exec "$(dirname "$0")/.slack-wrapped" "$@"
-  '';
-
-in stdenv.mkDerivation rec {
   name = "slack-cli-${version}";
   version = "0.18.0";
 
@@ -36,7 +23,21 @@ in stdenv.mkDerivation rec {
   installPhase = ''
     mkdir -p "$out/bin"
     cp src/slack "$out/bin/.slack-wrapped"
-      ln -s ${wrapper}/bin/slack "$out/bin/slack"
+
+    cat <<-WRAPPER > "$out/bin/slack"
+    #!${stdenv.shell}
+    [ "\$1" = "init" -a -z "\$SLACK_CLI_TOKEN" ] && cat <<-'MESSAGE' >&2
+    WARNING: slack-cli must be configured using the SLACK_CLI_TOKEN
+    environment variable. Using \`slack init\` will not work because it tries
+    to write to the Nix store.
+
+    MESSAGE
+
+    export PATH=${lib.makeBinPath [ curl jq ]}:"\$PATH"
+    exec "$out/bin/.slack-wrapped" "\$@"
+    WRAPPER
+
+    chmod +x "$out/bin/slack"
   '';
 
   meta = {
@@ -44,4 +45,4 @@ in stdenv.mkDerivation rec {
     maintainers = [ lib.maintainers.qyliss ];
     platforms = lib.platforms.unix;
   };
-  }
+}