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+---
+name: bash-53-features
+description: Bash 5.3 new features and modern patterns (2025)
+---
+
+## 🚨 CRITICAL GUIDELINES
+
+### Windows File Path Requirements
+
+**MANDATORY: Always Use Backslashes on Windows for File Paths**
+
+When using Edit or Write tools on Windows, you MUST use backslashes (`\`) in file paths, NOT forward slashes (`/`).
+
+**Examples:**
+- ❌ WRONG: `D:/repos/project/file.tsx`
+- ✅ CORRECT: `D:\repos\project\file.tsx`
+
+This applies to:
+- Edit tool file_path parameter
+- Write tool file_path parameter
+- All file operations on Windows systems
+
+
+### Documentation Guidelines
+
+**NEVER create new documentation files unless explicitly requested by the user.**
+
+- **Priority**: Update existing README.md files rather than creating new documentation
+- **Repository cleanliness**: Keep repository root clean - only README.md unless user requests otherwise
+- **Style**: Documentation should be concise, direct, and professional - avoid AI-generated tone
+- **User preference**: Only create additional .md files when user specifically asks for documentation
+
+
+---
+
+# Bash 5.3 Features (2025)
+
+## Overview
+
+Bash 5.3 (released July 2025) introduces significant new features that improve performance, readability, and functionality.
+
+## Key New Features
+
+### 1. In-Shell Command Substitution
+
+**New: ${ command; } syntax** - Executes without forking a subshell (runs in current shell context):
+
+```bash
+# OLD way (Bash < 5.3) - Creates subshell
+output=$(expensive_command)
+
+# NEW way (Bash 5.3+) - Runs in current shell, faster
+output=${ expensive_command; }
+```
+
+**Benefits:**
+- No subshell overhead (faster)
+- Preserves variable scope
+- Better performance in loops
+
+**Example:**
+```bash
+#!/usr/bin/env bash
+
+# Traditional approach
+count=0
+for file in *.txt; do
+    lines=$(wc -l < "$file")  # Subshell created
+    ((count += lines))
+done
+
+# Bash 5.3 approach (faster)
+count=0
+for file in *.txt; do
+    lines=${ wc -l < "$file"; }  # No subshell
+    ((count += lines))
+done
+```
+
+### 2. REPLY Variable Command Substitution
+
+**New: ${| command; } syntax** - Stores result in REPLY variable:
+
+```bash
+# Runs command, result goes to $REPLY automatically
+${| complex_calculation; }
+echo "Result: $REPLY"
+
+# Multiple operations
+${|
+    local_var="processing"
+    echo "$local_var: $((42 * 2))"
+}
+echo "Got: $REPLY"
+```
+
+**Use Cases:**
+- Avoid variable naming conflicts
+- Clean syntax for temporary values
+- Standardized result variable
+
+### 3. Enhanced `read` Builtin
+
+**New: -E option** - Uses readline with programmable completion:
+
+```bash
+# Interactive input with tab completion
+read -E -p "Enter filename: " filename
+# User can now tab-complete file paths!
+
+# With custom completion
+read -E -p "Select environment: " env
+# Enables full readline features (history, editing)
+```
+
+**Benefits:**
+- Better UX for interactive scripts
+- Built-in path completion
+- Command history support
+
+### 4. Enhanced `source` Builtin
+
+**New: -p PATH option** - Custom search path for sourcing:
+
+```bash
+# OLD way
+source /opt/myapp/lib/helpers.sh
+
+# NEW way - Search custom path
+source -p /opt/myapp/lib:/usr/local/lib helpers.sh
+
+# Respects CUSTOM_PATH instead of current directory
+CUSTOM_PATH=/app/modules:/shared/lib
+source -p "$CUSTOM_PATH" database.sh
+```
+
+**Benefits:**
+- Modular library organization
+- Avoid hard-coded paths
+- Environment-specific sourcing
+
+### 5. Enhanced `compgen` Builtin
+
+**New: Variable output option** - Store completions in variable:
+
+```bash
+# OLD way - Output to stdout
+completions=$(compgen -f)
+
+# NEW way - Directly to variable
+compgen -v completions_var -f
+# Results now in $completions_var
+```
+
+**Benefits:**
+- Cleaner completion handling
+- No extra subshells
+- Better performance
+
+### 6. GLOBSORT Variable
+
+**New: Control glob sorting behavior**:
+
+```bash
+# Default: alphabetical sort
+echo *.txt
+
+# Sort by modification time (newest first)
+GLOBSORT="-mtime"
+echo *.txt
+
+# Sort by size
+GLOBSORT="size"
+echo *.txt
+
+# Reverse alphabetical
+GLOBSORT="reverse"
+echo *.txt
+```
+
+**Options:**
+- `name` - Alphabetical (default)
+- `reverse` - Reverse alphabetical
+- `size` - By file size
+- `mtime` - By modification time
+- `-mtime` - Reverse modification time
+
+### 7. BASH_TRAPSIG Variable
+
+**New: Signal number variable in traps**:
+
+```bash
+#!/usr/bin/env bash
+set -euo pipefail
+
+# BASH_TRAPSIG contains the signal number being handled
+handle_signal() {
+    echo "Caught signal: $BASH_TRAPSIG" >&2
+    case "$BASH_TRAPSIG" in
+        15) echo "SIGTERM (15) received, shutting down gracefully" ;;
+        2)  echo "SIGINT (2) received, cleaning up" ;;
+        *)  echo "Signal $BASH_TRAPSIG received" ;;
+    esac
+}
+
+trap handle_signal SIGTERM SIGINT SIGHUP
+```
+
+**Benefits:**
+- Reusable signal handlers
+- Dynamic signal-specific behavior
+- Better logging and debugging
+
+### 8. Floating-Point Arithmetic
+
+**New: `fltexpr` loadable builtin**:
+
+```bash
+# Enable floating-point support
+enable -f /usr/lib/bash/fltexpr fltexpr
+
+# Perform calculations
+fltexpr result = 42.5 * 1.5
+echo "$result"  # 63.75
+
+# Complex expressions
+fltexpr pi_area = 3.14159 * 5 * 5
+echo "Area: $pi_area"
+```
+
+**Use Cases:**
+- Scientific calculations
+- Financial computations
+- Avoid external tools (bc, awk)
+
+## Performance Improvements
+
+### Avoid Subshells
+
+```bash
+# ❌ OLD (Bash < 5.3) - Multiple subshells
+for i in {1..1000}; do
+    result=$(echo "$i * 2" | bc)
+    process "$result"
+done
+
+# ✅ NEW (Bash 5.3+) - No subshells
+for i in {1..1000}; do
+    result=${ echo $((i * 2)); }
+    process "$result"
+done
+```
+
+**Performance Gain:** ~40% faster in benchmarks
+
+### Efficient File Processing
+
+```bash
+#!/usr/bin/env bash
+
+# Process large file efficiently
+process_log() {
+    local line_count=0
+    local error_count=0
+
+    while IFS= read -r line; do
+        ((line_count++))
+
+        # Bash 5.3: No subshell for grep
+        if ${ grep -q "ERROR" <<< "$line"; }; then
+            ((error_count++))
+        fi
+    done < "$1"
+
+    echo "Processed $line_count lines, found $error_count errors"
+}
+
+process_log /var/log/app.log
+```
+
+## Migration Guide
+
+### Check Bash Version
+
+```bash
+#!/usr/bin/env bash
+
+# Require Bash 5.3+
+if ((BASH_VERSINFO[0] < 5 || (BASH_VERSINFO[0] == 5 && BASH_VERSINFO[1] < 3))); then
+    echo "Error: Bash 5.3+ required (found $BASH_VERSION)" >&2
+    exit 1
+fi
+```
+
+### Feature Detection
+
+```bash
+# Test for 5.3 features
+has_bash_53_features() {
+    # Try using ${ } syntax
+    if eval 'test=${ echo "yes"; }' 2>/dev/null; then
+        return 0
+    else
+        return 1
+    fi
+}
+
+if has_bash_53_features; then
+    echo "Bash 5.3 features available"
+else
+    echo "Using legacy mode"
+fi
+```
+
+### Gradual Adoption
+
+```bash
+#!/usr/bin/env bash
+set -euo pipefail
+
+# Support both old and new bash
+if ((BASH_VERSINFO[0] > 5 || (BASH_VERSINFO[0] == 5 && BASH_VERSINFO[1] >= 3))); then
+    # Bash 5.3+ path
+    result=${ compute_value; }
+else
+    # Legacy path
+    result=$(compute_value)
+fi
+```
+
+## Best Practices (2025)
+
+1. **Use ${ } for performance-critical loops**
+   ```bash
+   for item in "${large_array[@]}"; do
+       processed=${ transform "$item"; }
+   done
+   ```
+
+2. **Use ${| } for clean temporary values**
+   ```bash
+   ${| calculate_hash "$file"; }
+   if [[ "$REPLY" == "$expected_hash" ]]; then
+       echo "Valid"
+   fi
+   ```
+
+3. **Enable readline for interactive scripts**
+   ```bash
+   read -E -p "Config file: " config
+   ```
+
+4. **Use source -p for modular libraries**
+   ```bash
+   source -p "$LIB_PATH" database.sh logging.sh
+   ```
+
+5. **Document version requirements**
+   ```bash
+   # Requires: Bash 5.3+ for performance features
+   ```
+
+## Compatibility Notes
+
+### Bash 5.3 Availability (2025)
+
+**Note:** Bash 5.3 (released July 2025) is the latest stable version. There is no Bash 5.4 as of October 2025.
+
+- **Linux**: Ubuntu 24.04+, Fedora 40+, Arch (current)
+- **macOS**: Homebrew (`brew install bash`)
+- **Windows**: WSL2 with Ubuntu 24.04+
+- **Containers**: `bash:5.3` official image
+
+### C23 Conformance
+
+Bash 5.3 updated to C23 language standard. **Note:** K&R style C compilers are no longer supported.
+
+### Fallback Pattern
+
+```bash
+#!/usr/bin/env bash
+set -euo pipefail
+
+# Detect bash version
+readonly BASH_53_PLUS=$((BASH_VERSINFO[0] > 5 || (BASH_VERSINFO[0] == 5 && BASH_VERSINFO[1] >= 3)))
+
+process_items() {
+    local item
+    for item in "$@"; do
+        if ((BASH_53_PLUS)); then
+            result=${ transform "$item"; }  # Fast path
+        else
+            result=$(transform "$item")      # Compatible path
+        fi
+        echo "$result"
+    done
+}
+```
+
+## Real-World Examples
+
+### Fast Log Parser
+
+```bash
+#!/usr/bin/env bash
+set -euo pipefail
+
+# Parse log file (Bash 5.3 optimized)
+parse_log() {
+    local file="$1"
+    local stats_errors=0
+    local stats_warnings=0
+    local stats_lines=0
+
+    while IFS= read -r line; do
+        ((stats_lines++))
+
+        # Fast pattern matching (no subshell)
+        ${| grep -q "ERROR" <<< "$line"; } && ((stats_errors++))
+        ${| grep -q "WARN" <<< "$line"; }  && ((stats_warnings++))
+    done < "$file"
+
+    echo "Lines: $stats_lines, Errors: $stats_errors, Warnings: $stats_warnings"
+}
+
+parse_log /var/log/application.log
+```
+
+### Interactive Configuration
+
+```bash
+#!/usr/bin/env bash
+set -euo pipefail
+
+# Interactive setup with readline
+setup_config() {
+    echo "Configuration Setup"
+    echo "==================="
+
+    # Tab completion for paths
+    read -E -p "Data directory: " data_dir
+    read -E -p "Config file: " config_file
+
+    # Validate and store
+    ${|
+        [[ -d "$data_dir" ]] && echo "valid" || echo "invalid"
+    }
+
+    if [[ "$REPLY" == "valid" ]]; then
+        echo "DATA_DIR=$data_dir" > config.env
+        echo "CONFIG_FILE=$config_file" >> config.env
+        echo "✓ Configuration saved"
+    else
+        echo "✗ Invalid directory" >&2
+        return 1
+    fi
+}
+
+setup_config
+```
+
+## Resources
+
+- [Bash 5.3 Release Notes](https://lists.gnu.org/archive/html/bash-announce/2025-07/msg00000.html)
+- [Bash Manual - Command Substitution](https://www.gnu.org/software/bash/manual/html_node/Command-Substitution.html)
+- [ShellCheck Bash 5.3 Support](https://github.com/koalaman/shellcheck/releases)
+
+---
+
+**Bash 5.3 provides significant performance and usability improvements. Adopt these features gradually while maintaining backwards compatibility for older systems.**