CONFIG-003: Consolidate Duplicate Aliases

Category: Configuration / Maintainability Severity: Warning Since: v6.1.0 Fixable: Yes (automatic)

Problem

Shell configuration files often accumulate duplicate alias definitions over time as users experiment with different settings. When the same alias is defined multiple times:

  • Confusing behavior: Only the last definition takes effect
  • Maintenance burden: Harder to track which aliases are active
  • Cluttered configs: Unnecessary duplication
  • Debugging difficulty: Hard to find which alias definition is "winning"

Example Problem

 Early in .bashrc
alias ls='ls --color=auto'
alias ll='ls -la'

 ... 100 lines later ...

 Forgot about the first one!
alias ls='ls -G'           # This one wins
alias ll='ls -alh'         # This one wins

The second definitions override the first ones, but both remain in the file causing confusion.

Detection

Rash analyzes all alias definitions and detects when the same alias name appears multiple times:

bashrs config analyze messy.bashrc

Output:

[CONFIG-003] Duplicate alias definition: 'ls'
  → Line: 21
  → First occurrence: Line 17
  → Severity: Warning
  → Suggestion: Remove earlier definition or rename alias. Last definition wins in shell.

Automatic Fix

Rash can automatically consolidate duplicates, keeping only the last definition (matching shell behavior):

bashrs config purify messy.bashrc --output clean.bashrc

Before:

alias ll='ls -la'
alias ls='ls --color=auto'
alias ll='ls -alh'         # Duplicate
alias grep='grep --color=auto'
alias ll='ls -lAh'         # Duplicate

After:

alias ls='ls --color=auto'
alias grep='grep --color=auto'
alias ll='ls -lAh'         # Only the last definition kept

Why Last Definition Wins

CONFIG-003 follows shell behavior where later alias definitions override earlier ones:

 In shell
$ alias ls='ls --color=auto'
$ alias ls='ls -G'
$ alias ls
alias ls='ls -G'           # Only the last one is active

This matches how shells process config files line-by-line.

Implementation

The consolidation algorithm:

use std::collections::HashMap;
use regex::Regex;

/// Consolidate duplicate aliases, keeping only the last definition
pub fn consolidate_aliases(source: &str) -> String {
    let aliases = analyze_aliases(source);

    if aliases.is_empty() {
        return source.to_string();
    }

    // Build map of alias names to their last definition line
    let mut last_definition: HashMap<String, usize> = HashMap::new();
    for alias in &aliases {
        last_definition.insert(alias.name.clone(), alias.line);
    }

    // Build set of lines to skip (duplicates)
    let mut lines_to_skip = Vec::new();
    for alias in &aliases {
        if let Some(&last_line) = last_definition.get(&alias.name) {
            if alias.line != last_line {
                // This is not the last definition - skip it
                lines_to_skip.push(alias.line);
            }
        }
    }

    // Reconstruct source, skipping duplicate lines
    let mut result = Vec::new();
    for (line_num, line) in source.lines().enumerate() {
        let line_num = line_num + 1;

        if lines_to_skip.contains(&line_num) {
            continue; // Skip this duplicate
        }

        result.push(line.to_string());
    }

    result.join("\n")
}

// Helper types
struct AliasDefinition {
    line: usize,
    name: String,
    value: String,
}

fn analyze_aliases(source: &str) -> Vec<AliasDefinition> {
    // Implementation details...
    vec![]
}

Testing

CONFIG-003 has comprehensive tests:

#[test]
fn test_config_003_consolidate_simple() {
    // ARRANGE
    let source = r#"alias ls='ls --color=auto'
alias ls='ls -G'"#;

    // ACT
    let result = consolidate_aliases(source);

    // ASSERT
    assert_eq!(result, "alias ls='ls -G'");
}

#[test]
fn test_config_003_consolidate_multiple() {
    // ARRANGE
    let source = r#"alias ll='ls -la'
alias ls='ls --color=auto'
alias ll='ls -alh'
alias grep='grep --color=auto'
alias ll='ls -lAh'"#;

    let expected = r#"alias ls='ls --color=auto'
alias grep='grep --color=auto'
alias ll='ls -lAh'"#;

    // ACT
    let result = consolidate_aliases(source);

    // ASSERT
    assert_eq!(result, expected);
}

#[test]
fn test_config_003_idempotent() {
    // ARRANGE
    let source = r#"alias ls='ls --color=auto'
alias ls='ls -G'"#;

    // ACT
    let consolidated_once = consolidate_aliases(source);
    let consolidated_twice = consolidate_aliases(&consolidated_once);

    // ASSERT
    assert_eq!(
        consolidated_once, consolidated_twice,
        "Consolidation should be idempotent"
    );
}

Real-World Example

Common scenario in a 5-year-old .bashrc:

 Original setup (2019)
alias ll='ls -la'
alias ls='ls --color=auto'
alias grep='grep --color=auto'

 Tried new options (2020)
alias ll='ls -lah'

 macOS-specific (2021)
alias ls='ls -G'

 Final preference (2023)
alias ll='ls -lAh'

After purification:

 Consolidated aliases
alias ls='ls -G'
alias grep='grep --color=auto'
alias ll='ls -lAh'

Three duplicate definitions reduced to three clean aliases.

CLI Usage

 Analyze for duplicates
bashrs config analyze ~/.bashrc

 Lint and exit with error code if found
bashrs config lint ~/.bashrc

 Preview what would be fixed
bashrs config purify ~/.bashrc --dry-run

 Apply fixes with backup (default: ~/.bashrc.backup.TIMESTAMP)
bashrs config purify ~/.bashrc --fix

 Apply without backup (dangerous!)
bashrs config purify ~/.bashrc --fix --no-backup

 Output to different file
bashrs config purify ~/.bashrc --output ~/.bashrc.clean

Configuration

You can control CONFIG-003 behavior through CLI flags:

 Dry-run to preview changes (default)
bashrs config purify ~/.bashrc --dry-run

 Apply with backup
bashrs config purify ~/.bashrc --fix

 Skip backup (not recommended)
bashrs config purify ~/.bashrc --fix --no-backup

 JSON output for tooling
bashrs config analyze ~/.bashrc --format json

Edge Cases

Comments Between Duplicates

 Before
alias ls='ls --color=auto'
 This is my preferred ls
alias ls='ls -G'

 After
 This is my preferred ls
alias ls='ls -G'

Comments and blank lines are preserved.

Mixed Quote Styles

 Before
alias ls='ls --color=auto'    # Single quotes
alias ls="ls -G"               # Double quotes

 After
alias ls="ls -G"               # Both styles supported

CONFIG-003 handles both single and double quotes.

No Duplicates

If no duplicates exist, the file is unchanged:

alias ll='ls -la'
alias ls='ls --color=auto'
alias grep='grep --color=auto'
 No changes needed

Performance

CONFIG-003 is highly optimized:

  • Regex-based: O(n) scanning with compiled regex
  • Single pass: Analyzes and consolidates in one pass
  • Idempotent: Safe to run multiple times
  • Fast: ~1ms for typical .bashrc files

FAQ

Q: Why keep the last definition instead of the first?

A: The last definition is what's actually active in your shell. Keeping it matches real behavior and is what users typically intend (later overrides earlier).

Q: What if I have conditional aliases?

A: CONFIG-003 only consolidates identical alias names. Conditional aliases are preserved:

if [ "$OS" = "Darwin" ]; then
    alias ls='ls -G'
else
    alias ls='ls --color=auto'
fi
 Both kept - they're conditional

Q: Can I disable this rule?

A: Currently, rules cannot be disabled individually. This feature is planned for v7.1.

Q: What about functions with the same name as aliases?

A: CONFIG-003 only analyzes alias definitions. Functions are handled separately.

Best Practices

✅ DO:

  • Run bashrs config analyze before manual edits
  • Use --dry-run to preview changes first
  • Keep backups (default behavior)
  • Consolidate regularly during config maintenance

❌ DON'T:

  • Skip the dry-run step
  • Disable backups unless you're certain
  • Edit config while shell is sourcing it
  • Ignore CONFIG-003 warnings (they indicate confusion)

See Also