Add feature to edit existing tasks

Author: coderick14

README.md

@@ -12,7 +12,7 @@ Type `tusker help` to get started.
 ```
 tusker add "The task that I would've forgotten"
 ```
-- Show current tasks *[ID, Status, Description, CreatedAt]*
+- Show current tasks *[ID, Status, Description, UpdatedAt]*
 ```
 tusker show
      1	❌      Collect laundry                  25 April 2018 11:53:21
@@ -35,6 +35,14 @@ tusker show
      2	❌      Collect NOC certificate          25 April 2018 11:53:23
      3	❌      Fill rems                        25 April 2018 11:53:25
 ```
+- Edit the description for an existing task
+```
+tusker edit 3 Fill rems and forms
+tusker show
+     1	❌      Collect laundry                  25 April 2018 11:53:21
+     2	❌      Collect NOC certificate          25 April 2018 11:53:23
+     3	❌      Fill rems and forms              25 April 2018 11:53:25
+```
 - Delete one or more tasks from the list
 ```
 tusker del 1 3

tusker

@@ -15,6 +15,7 @@ HELP_MSG="
     Mark a task as done   : tusker check TASK_ID
     Mark a task as undone : tusker uncheck TASK_ID
     Delete a task         : tusker del TASK_ID
+    Edit task description : tusker edit TASK_ID NEW_TASK_DESCRIPTION
     Show existing tasks   : tusker show
 "
 
@@ -75,6 +76,15 @@ uncheck_task() {
     done
 }
 
+edit_task() {
+    task_id="$1"
+    shift
+    task_desc="$*"
+    current_timestamp=$(date +"%d %B %Y %H:%M:%S")
+    task_string="$CROSS $DELIM   $task_desc $DELIM  $current_timestamp"
+    sed -i "$task_id s/.*/$task_string/" "$FILE_NAME"
+}
+
 show_tasks() {
     line_count=$(wc -l $FILE_NAME | awk '{print $1}')
 
@@ -98,8 +108,8 @@ main() {
         shift
         add_task "$*"
         printf "Task added\n"
-        ;;
 
+        ;;
         del)
         shift
         delete_task "$@"
@@ -118,6 +128,12 @@ main() {
         printf "Task(s) marked as undone\n"
         ;;
 
+        edit)
+        shift
+        edit_task "$@"
+        printf "Task edited\n"
+        ;;
+
         show)
         show_tasks
         ;;