Add addp command for adding tasks with priority

- Implement addp PRIORITY "TASK" syntax to add tasks with specified priority (A-Z)
- Priority is automatically converted to uppercase and formatted as (PRIORITY)
- Add comprehensive error handling for invalid priorities (numbers, special chars, multiple chars)
- Integrate with existing features like TODOTXT_DATE_ON_ADD and configuration options
- Update help documentation in shorthelp() and actionsHelp()
- Add complete documentation to USAGE.md with examples and usage patterns
- Add comprehensive test suite (t1050-addp.sh) with 23 test cases covering:
  - Basic functionality and priority validation
  - Case conversion (lowercase to uppercase)
  - Integration with projects and contexts
  - Error handling for all invalid input scenarios
  - Configuration integration (date on add, priority on add overrides)
  - Edge cases with special characters and quotes

Example usage:
  todo.sh addp A "High priority task"     # Creates: (A) High priority task
  todo.sh addp c "Medium priority task"   # Creates: (C) Medium priority task

Author: rosconap

USAGE.md

@@ -28,6 +28,22 @@ todo.sh addm "FIRST THING I NEED TO DO +project1 @context
 SECOND THING I NEED TO DO +project2 @context"
 ```
 
+### `addp`
+Adds TEXT TO ADD to your todo.txt file on its own line with the specified PRIORITY (A-Z) at the beginning.
+
+The priority letter is automatically converted to uppercase and formatted as `(PRIORITY)`.
+
+```shell
+todo.sh addp A "Important high-priority task"
+todo.sh addp e "Medium priority task"
+```
+
+Example output:
+```
+(A) Important high-priority task
+(E) Medium priority task
+```
+
 ### `addto`
 Adds a line of text to any file located in the todo.txt directory.
 

tests/t1050-addp.sh

@@ -0,0 +1,165 @@
+#!/usr/bin/env bash
+
+test_description='addp command functionality
+
+Tests the addp command which adds tasks with specified priority.
+'
+. ./test-lib.sh
+
+# Test basic addp functionality
+test_todo_session 'basic addp functionality' <<EOF
+>>> todo.sh addp A "High priority task"
+1 (A) High priority task
+TODO: 1 added.
+
+>>> todo.sh addp B "Medium priority task"
+2 (B) Medium priority task
+TODO: 2 added.
+
+>>> todo.sh addp Z "Low priority task"
+3 (Z) Low priority task
+TODO: 3 added.
+
+>>> todo.sh -p list
+1 (A) High priority task
+2 (B) Medium priority task
+3 (Z) Low priority task
+--
+TODO: 3 of 3 tasks shown
+EOF
+
+# Test lowercase priority conversion
+cat > todo.txt <<EOF
+EOF
+test_todo_session 'lowercase priority conversion' <<EOF
+>>> todo.sh addp c "lowercase priority test"
+1 (C) lowercase priority test
+TODO: 1 added.
+
+>>> todo.sh addp z "another lowercase test"
+2 (Z) another lowercase test
+TODO: 2 added.
+
+>>> todo.sh -p list
+1 (C) lowercase priority test
+2 (Z) another lowercase test
+--
+TODO: 2 of 2 tasks shown
+EOF
+
+# Test addp with projects and contexts
+cat > todo.txt <<EOF
+EOF
+test_todo_session 'addp with projects and contexts' <<EOF
+>>> todo.sh addp A "Important work task +project @work"
+1 (A) Important work task +project @work
+TODO: 1 added.
+
+>>> todo.sh addp B "Call client +client @phone"
+2 (B) Call client +client @phone
+TODO: 2 added.
+
+>>> todo.sh -p list
+1 (A) Important work task +project @work
+2 (B) Call client +client @phone
+--
+TODO: 2 of 2 tasks shown
+EOF
+
+# Test error handling - no arguments
+cat > todo.txt <<EOF
+EOF
+test_todo_session 'addp error - no arguments' <<EOF
+>>> todo.sh addp
+usage: todo.sh addp PRIORITY "TODO ITEM"
+=== 1
+EOF
+
+# Test error handling - missing task text
+test_todo_session 'addp error - missing task text' <<EOF
+>>> todo.sh addp A
+usage: todo.sh addp PRIORITY "TODO ITEM"
+=== 1
+EOF
+
+# Test error handling - invalid priority (number)
+test_todo_session 'addp error - invalid priority number' <<EOF
+>>> todo.sh addp 1 "Invalid priority task"
+TODO: Priority must be a letter from A to Z (got: 1)
+=== 1
+EOF
+
+# Test error handling - invalid priority (multiple characters)
+test_todo_session 'addp error - invalid priority multiple chars' <<EOF
+>>> todo.sh addp AA "Invalid priority task"
+TODO: Priority must be a letter from A to Z (got: AA)
+=== 1
+EOF
+
+# Test error handling - invalid priority (special character)
+test_todo_session 'addp error - invalid priority special char' <<EOF
+>>> todo.sh addp @ "Invalid priority task"
+TODO: Priority must be a letter from A to Z (got: @)
+=== 1
+EOF
+
+# Test addp integration with date_on_add
+cat > todo.txt <<EOF
+EOF
+echo "export TODOTXT_DATE_ON_ADD=1" >> todo.cfg
+
+test_todo_session 'addp with date on add' <<EOF
+>>> todo.sh addp A "Task with date"
+1 (A) $(date '+%Y-%m-%d') Task with date
+TODO: 1 added.
+
+>>> todo.sh -p list
+1 (A) $(date '+%Y-%m-%d') Task with date
+--
+TODO: 1 of 1 tasks shown
+EOF
+
+# Reset config for next test
+echo "export TODOTXT_DATE_ON_ADD=0" >> todo.cfg
+
+# Test that addp overrides TODOTXT_PRIORITY_ON_ADD
+cat > todo.txt <<EOF
+EOF
+echo "export TODOTXT_PRIORITY_ON_ADD=C" >> todo.cfg
+
+test_todo_session 'addp overrides PRIORITY_ON_ADD' <<EOF
+>>> todo.sh addp A "Priority A task"
+1 (A) Priority A task
+TODO: 1 added.
+
+>>> todo.sh add "Normal add task"
+2 (C) Normal add task
+TODO: 2 added.
+
+>>> todo.sh -p list
+1 (A) Priority A task
+2 (C) Normal add task
+--
+TODO: 2 of 2 tasks shown
+EOF
+
+# Test addp with various edge cases
+cat > todo.txt <<EOF
+EOF
+test_todo_session 'addp edge cases' <<EOF
+>>> todo.sh addp E "Task with special chars: !@#$%^&*()"
+1 (E) Task with special chars: !@#$%^&*()
+TODO: 1 added.
+
+>>> todo.sh addp F "Task with 'single quotes' and \"double quotes\""
+2 (F) Task with 'single quotes' and "double quotes"
+TODO: 2 added.
+
+>>> todo.sh -p list
+1 (E) Task with special chars: !@#$%^&*()
+2 (F) Task with 'single quotes' and "double quotes"
+--
+TODO: 2 of 2 tasks shown
+EOF
+
+test_done

todo.sh

@@ -45,6 +45,7 @@ shorthelp()
 		    add|a "THING I NEED TO DO +project @context"
 		    addm "THINGS I NEED TO DO
 		          MORE THINGS I NEED TO DO"
+		    addp PRIORITY "TEXT TO ADD"
 		    addto DEST "TEXT TO ADD"
 		    append|app NR "TEXT TO APPEND"
 		    archive
@@ -177,6 +178,11 @@ actionsHelp()
 		      Adds SECOND THING I NEED TO DO to you todo.txt on its own line.
 		      Project and context notation optional.
 
+		    addp PRIORITY "TEXT TO ADD"
+		      Adds TEXT TO ADD to your todo.txt file on its own line with
+		      the specified PRIORITY (A-Z) at the beginning.
+		      For example, addp A "Important task" creates "(A) Important task".
+
 		    addto DEST "TEXT TO ADD"
 		      Adds a line of text to any file located in the todo.txt directory.
 		      For example, addto inbox.txt "decide about vacation"
@@ -1120,6 +1126,29 @@ case $action in
     IFS=$SAVEIFS
     ;;
 
+"addp")
+    errmsg="usage: $TODO_SH addp PRIORITY \"TODO ITEM\""
+    [ -z "$2" ] && die "$errmsg"
+    priority="$2"
+    [ -z "$3" ] && die "$errmsg"
+    
+    # Validate priority is a single letter A-Z
+    if ! echo "$priority" | grep -q '^[A-Za-z]$'; then
+        die "TODO: Priority must be a letter from A to Z (got: $priority)"
+    fi
+    
+    # Convert to uppercase
+    priority=$(echo "$priority" | tr '[:lower:]' '[:upper:]')
+    
+    shift 2
+    input="$*"
+    
+    # Add priority prefix to input
+    input="($priority) $input"
+    
+    _addto "$TODO_FILE" "$input"
+    ;;
+
 "addto" )
     errmsg="usage: $TODO_SH addto DEST \"TODO ITEM\""
     [ -z "$2" ] && die "$errmsg"