Add sample shell script to commit-msg script

To ensure commit messages are written with a clear description, a
sample shell script is added to the commit-msg script. The script
checks if the commit message follows the rules set on
https://chris.beams.io/posts/git-commit/#seven-rules and aborts the
commit if the rules are broken.

The script should not check git commit messages that has the '-m' tag,
since the tag can be used for commits that does not require
extensive explanation.

.githooks/commit-msg

@@ -0,0 +1,39 @@
+#!/bin/bash
+#found in https://www.reddit.com/r/bash/comments/8inq6i/validate_git_commit_message/, contributed by user frakman1
+#rules based on https://chris.beams.io/posts/git-commit/#seven-rules
+
+echo -e "\e[32m--- Checking Commit Message ---\e[0m";
+
+cnt=0
+while IFS='' read -r line || [[ -n "$line" ]]; do
+  cnt=$((cnt+1))
+  length=${#line}
+  if [ $cnt -eq 1 ]; then
+    # Checking if subject exceeds 50 characters
+    if [ $length -gt 50 ]; then
+      echo -e "\e[31m*** Subject line exceeds 50 characters ***\e[0m";
+      exit 1
+    fi
+    i=$(($length-1))
+    last_char=${line:$i:1}
+    # Last character must not have a punctuation
+    if [[ ! $last_char =~ [0-9a-zA-Z] ]]; then
+      echo -e "\e[31m*** Last character of subject line must not contain punctuation ***\e[0m";
+      exit 1
+    fi
+  elif [ $cnt -eq 2 ]; then
+    # Subject must be followed by a blank line
+    if [ $length -ne 0 ]; then
+      echo -e "\e[31m*** Current subject line follows a non-empty line. Subject lines should always be followed by a blank line ***\e[0m";
+      exit 1
+    fi
+  else
+    # Any line in body must not exceed 72 characters
+    if [ $length -gt 72 ]; then
+      echo -e "\e[31m*** Line \"$line\" exceeds 72 characters ***\e[0m";
+      exit 1
+    fi
+  fi
+done < "$1"
+
+