scripts: added a script to download the latest release

This script downloads the latest release from a remote Github repository
into the current directory.

Invoke './scripts/get_latest_release.sh' to get the latest release in the
local repository directory.

README.md

@@ -2,4 +2,10 @@
 
 Repository for WRS firmware releases used in GSI.
 
-The latest release in usage is labeled as 'latest' in Releases.
+## Usage
+
+Download the latest release into the local repository directory:
+
+```
+$ ./scripts/get_latest_release.sh
+```

scripts/get_latest_release.sh

@@ -0,0 +1,43 @@
+#!/bin/bash
+
+# Download the latest WRS release (tarball) from the Github repo
+
+# URLs
+url_repo_api="https://api.github.com/repos/GSI-CS-CO/wrs-gsi-releases"
+url_latest_api="$url_repo_api/releases/latest"
+
+# Get the information about the latest release
+
+latest_release_api=$(curl -s $url_latest_api)
+#echo $latest_release_api
+
+# Extract a download URL from the release information
+
+url_download=$(echo $latest_release_api | sed -e 's/.*"browser_download_url": "\([^"]*\)".*/\1/')
+#url_download=$(echo $latest_release_api | sed -E 's/.*"browser_download_url": "?([^,"]*)"?.*/\1/')  # works too
+#echo $url_download
+
+# Download a target tarball
+
+wget -nc $url_download
+
+# Command options
+
+# curl options:
+# -L: redirect to moved location
+# -s: silent
+
+# sed options:
+# -e: basic expression
+# s/regexp/replacement/[flags]: attempt to match the pattern space against 'regexp'
+#              if the match found, then that portion is replaced with 'replacement'
+# \1: in 'replacement' it refers to a portion of the match which is contained
+#              between the 'n'th and '\)' and its matching '\)'
+# [^"]: bracket subexpression that excludes '"' from list
+# \(regexp\): groups 'regexp' as a whole
+# \([^"]*\): all characters until first '"'
+
+# -E: extended regular expression
+
+# wget options:
+# -nc: prevent download an existing target file