shell scripts: fix shebangs, move docker-related variables into docke…

…r condition (#16)

* *.sh: use /usr/bin/env bash as shebang

This allows these to execute in environments where `bash` is in `$PATH`
(but not necessarily in /usr/bin), such as NixOS.

* gen.sh, serve.sh: move docker image variables into docker codepath

There's few point in setting these if docker isn't found.

gen.sh

@@ -1,22 +1,22 @@
-#!/bin/bash
+#!/usr/bin/env bash
 # Copyright 2017 The Periph Authors. All rights reserved.
 # Use of this source code is governed under the Apache License, Version 2.0
 # that can be found in the LICENSE file.
 
 set -eu
 cd "$(dirname $0)"
 
-# Determine the docker image to use.
-TAG="$(cat ./tag)"
-IMAGE="marcaruel/hugo-tidy:${TAG}"
-
 echo "Tips:"
 echo " - Use --buildDrafts to render drafts."
 
 # Only use docker if not passing a flag, otherwise the container doesn't work as
 # expected.
 if [ $# == 0 ]; then
   if (which docker > /dev/null); then
+    # Determine the docker image to use.
+    TAG="$(cat ./tag)"
+    IMAGE="marcaruel/hugo-tidy:${TAG}"
+
     echo "Using hugo-tidy"
     # See https://github.com/maruel/hugo-tidy/ for more info.
     # First, pull the image only if missing.

new_post.sh

@@ -1,4 +1,4 @@
-#!/bin/bash
+#!/usr/bin/env bash
 # Copyright 2020 The Periph Authors. All rights reserved.
 # Use of this source code is governed under the Apache License, Version 2.0
 # that can be found in the LICENSE file.

serve.sh

@@ -1,21 +1,21 @@
-#!/bin/bash
+#!/usr/bin/env bash
 # Copyright 2017 The Periph Authors. All rights reserved.
 # Use of this source code is governed under the Apache License, Version 2.0
 # that can be found in the LICENSE file.
 
 set -eu
 cd "$(dirname $0)"
 
-# Determine the docker image to use.
-TAG="$(cat ./tag)"
-IMAGE="marcaruel/hugo-tidy:${TAG}"
-
 echo "Tips:"
 echo " - Use --bind=0.0.0.0 to be accessible on the local network."
 echo " - Use --buildDrafts to render drafts."
 
 if (which docker > /dev/null); then
   echo "Using hugo-tidy"
+  # Determine the docker image to use.
+  TAG="$(cat ./tag)"
+  IMAGE="marcaruel/hugo-tidy:${TAG}"
+
   # See https://github.com/maruel/hugo-tidy/ for more info.
   # First, pull the image only if missing.
   [ ! -z $(docker images -q "${IMAGE}") ] || docker pull "${IMAGE}"