scripts/latest.sh: script to edit latest.txt

This script supports 'get', 'put' and 'vi' commands to edit the file at
http://releases.wagtail.io/latest.txt.  Usage is fairly straightforward:

$ scripts/latest.sh get my-latest.txt
$ vi my-latest.txt
$ scripts/latest.sh put my-latest.txt

Or, in a single command (equivalent to get, vi and put):

$ scripts/latest.sh vi

'put' will automatically create a CloudFront invalidation, that
typically takes around 15 minutes to fully deploy

TODO: documentation; script to create a template latest.txt based on
      command-line arguments.

scripts/latest.sh

@@ -0,0 +1,129 @@
+#! /bin/sh
+# vim:sw=4 ts=4 et:
+
+BUCKET=releases.wagtail.io
+REGION=eu-west-1
+CF_DISTRIBUTION=E283SZ5CB4MDM0
+
+# Find the location of the AWS CLI binary.  MacPorts sometimes put it in a
+# weird place, so to be helpful we check those locations as well.
+if [ -z "${AWS_CLI}" ]; then
+    for d in $(echo "${PATH}" | tr ':' ' ')                             \
+        /opt/local/Library/Frameworks/Python.framework/Versions/2.7/bin \
+        /opt/local/Library/Frameworks/Python.framework/Versions/3.4/bin \
+        ; do
+        if [ -x "${d}/aws" ]; then
+            AWS_CLI="${d}/aws"
+            break
+        fi
+    done
+
+    if [ -z "${AWS_CLI}" ]; then
+        printf >&2 -- '%s: cannot find AWS CLI binary "aws"\n' "$0"
+        printf >&2 -- '%s: please install AWS from http://aws.amazon.com/documentation/cli/\n' "$0"
+        exit 1
+    fi
+fi
+
+# CloudFront support in the CLI is still in beta.
+$AWS_CLI configure set preview.cloudfront true
+
+_usage() {
+    printf >&2 -- 'usage: %s get       [output-filename]\n' "$0"
+    printf >&2 -- '       %s put       [input-filename]\n' "$0"
+    printf >&2 -- '       %s <vi|edit>\n' "$0"
+}
+
+if [ "$#" -lt 1 ]; then
+    _usage
+    exit 1
+fi
+
+_get() {
+    if ! $AWS_CLI s3 cp --region "${REGION}" "s3://${BUCKET}/latest.txt" "$1"; then
+        printf >&2 -- "%s: failed to download latest.txt; see above messages\\n" "$0"
+        exit 1
+    fi
+}
+
+_put() {
+    if ! $AWS_CLI s3 cp --region "${REGION}" "$1" "s3://${BUCKET}/latest.txt"; then
+        printf >&2 -- "%s: failed to upload latest.txt; see above messages\\n" "$0"
+        exit 1
+    fi
+
+    $AWS_CLI >/dev/null cloudfront create-invalidation  \
+        --distribution-id "$CF_DISTRIBUTION"            \
+        --invalidation-batch                            \
+'{
+    "Paths": {
+        "Items": [
+            "/latest.txt"
+        ],
+    "Quantity": 1
+    },
+    "CallerReference": "latest.sh"
+}'
+}
+
+if [ "$1" = "get" ]; then
+    if [ "$#" -lt 2 ]; then
+        _usage
+        exit 1
+    fi
+
+    shift
+
+    if [ -e "$2" ]; then
+        printf >&2 -- "%s: \"%s\": already exists, won't overwrite\\n" "$0"
+        exit 1
+    fi
+
+    _get "$@"
+elif [ "$1" = "put" ]; then
+    if [ "$#" -lt 2 ]; then
+        _usage
+        exit 1
+    fi
+
+    shift
+
+    _put "$@"
+elif [ "$1" = "edit" -o "$1" = "vi" ]; then
+    LTMP=$(mktemp "${TMPDIR:-/tmp}/latest.XXXXXX")
+    if [ "$?" -ne 0 ]; then
+        printf >&2 -- '%s: cannot create temporary file\n' "$0"
+        exit 1
+    fi
+    trap 'rm -f "${LTMP}"' 0 EXIT INT
+
+    LTMP2=$(mktemp "${TMPDIR:-/tmp}/latest.XXXXXX")
+    if [ "$?" -ne 0 ]; then
+        printf >&2 -- '%s: cannot create temporary file\n' "$0"
+        exit 1
+    fi
+    trap 'rm -f "${LTMP2}"' 0 EXIT INT
+
+    if ! _get "${LTMP}"; then
+        exit 1
+    fi
+    
+    cp "${LTMP}" "${LTMP2}"
+
+    if [ ! -z "${VISUAL}" ]; then
+        editor="${VISUAL}"
+    elif [ ! -z "${EDITOR}" ]; then
+        editor="${EDITOR}"
+    else
+        editor='vi'
+    fi
+
+    $editor "${LTMP}"
+    if cmp "${LTMP}" "${LTMP2}" >/dev/null; then
+        printf >&2 -- '%s: no changes; exiting\n' "$0"
+        exit 1
+    fi
+
+    diff -u "${LTMP2}" "${LTMP}"
+    _put "${LTMP}"
+fi