AgentSkillsCN

Bash To Script

Bash To Script

SKILL.md

Bash to Script File Converter Skill

Purpose: Convert bash commands with parameter expansion or complex syntax to script file format to avoid parse errors in the Bash tool.

When to Use:

  • •When bash command fails with parse error: (eval):1: parse error near '('
  • •Before executing commands with ${VAR##pattern} or ${VAR%%pattern} syntax
  • •When using complex jq pipelines with command substitution
  • •When bash command has multiple nested parameter expansions
  • •Proactively for any bash command pattern known to cause issues

Problem

The Bash tool has limitations with certain bash syntax patterns, particularly:

  • •Parameter expansion with pattern removal: ${VAR##prefix}, ${VAR%%suffix}
  • •Complex command substitution: $(jq ... | tail -1)
  • •Nested parameter expansions in single command
  • •Heredoc with complex variable interpolation

These patterns can fail with cryptic parse errors when executed directly via the Bash tool.

Solution

Convert the problematic command to a script file approach:

  1. •Write command to temporary script file using heredoc
  2. •Execute the script file with bash /tmp/script.sh
  3. •Script file handles all parameter expansion correctly

Usage

Input Required:

  • •The bash command that needs conversion (as a string)
  • •Optional: Script filename (defaults to /tmp/converted-script.sh)

Output:

  • •Converted command using script file approach
  • •Ready to execute via Bash tool

Conversion Instructions

When you encounter a bash command that needs conversion, follow this pattern:

bash
# Original problematic command (example):
SESSION_ID="abc-123"
AGENT_ID=$(jq -r 'select(.toolUseResult.agentId)' /path/${SESSION_ID}.jsonl | tail -1)
echo "$AGENT_ID" > output.txt

# Convert to script file approach:
cat > /tmp/converted-script.sh << 'EOF'
#!/bin/bash
SESSION_ID="abc-123"
AGENT_ID=$(jq -r 'select(.toolUseResult.agentId)' /path/${SESSION_ID}.jsonl | tail -1)
echo "$AGENT_ID" > output.txt
EOF
bash /tmp/converted-script.sh

Automatic Conversion

To invoke this skill for automatic conversion:

code
Skill: bash-to-script
Command: <paste the problematic bash command here>

The skill will output the converted command ready to execute.

Pattern Recognition

Commands that need conversion (automatic detection patterns):

  1. •

    Parameter Expansion with Pattern Removal:

    bash
    ${VAR##prefix*}    # Remove longest matching prefix
${VAR%%*suffix}    # Remove longest matching suffix
${VAR#prefix}      # Remove shortest matching prefix
${VAR%suffix}      # Remove shortest matching suffix
  2. •

    Complex Command Substitution:

    bash
    VAR=$(complex command | pipeline | tail -1)
# Especially with jq, grep, awk, sed pipelines
  3. •

    Multiple Parameter Expansions:

    bash
    echo "${VAR1}" > /path/to/${VAR2}/file-${VAR3}.txt
# Multiple expansions in single command
  4. •

    Nested Quotes with Variables:

    bash
    jq -r 'select(.field == "'"$VAR"'")' file.json
# Nested single/double quotes with variable interpolation

Conversion Template

Standard template for conversion:

bash
cat > /tmp/<descriptive-name>.sh << 'EOF'
#!/bin/bash
set -euo pipefail

# Your original command(s) here
# All parameter expansion works correctly in script file

EOF
bash /tmp/<descriptive-name>.sh

With error handling:

bash
cat > /tmp/<descriptive-name>.sh << 'EOF'
#!/bin/bash
set -euo pipefail
trap 'echo "ERROR in script at line $LINENO: Command failed: $BASH_COMMAND" >&2; exit 1' ERR

# Your original command(s) here

EOF
bash /tmp/<descriptive-name>.sh

Examples

Example 1: Parameter Expansion with Pattern Removal

❌ Fails with parse error:

bash
BACKUP_FILE=$(ls /workspace/CLAUDE.md.backup-* 2>/dev/null | tail -1)
VALIDATION_ID="${BACKUP_FILE##*.backup-}"
echo "$VALIDATION_ID"

✅ Correct (converted):

bash
cat > /tmp/extract-validation-id.sh << 'EOF'
#!/bin/bash
BACKUP_FILE=$(ls /workspace/CLAUDE.md.backup-* 2>/dev/null | tail -1)
VALIDATION_ID="${BACKUP_FILE##*.backup-}"
echo "$VALIDATION_ID"
EOF
bash /tmp/extract-validation-id.sh

Example 2: Complex jq Pipeline

❌ Fails with parse error:

bash
SESSION_ID="7f08a8f6-b90c-47ac-bc1b-31943c7b995a"
AGENT_ID=$(jq -r 'select(.toolUseResult.agentId) | .toolUseResult.agentId' /home/node/.config/projects/-workspace/${SESSION_ID}.jsonl 2>/dev/null | tail -1)
echo "$AGENT_ID" > /tmp/agent-id.txt

✅ Correct (converted):

bash
cat > /tmp/extract-agent-id.sh << 'EOF'
#!/bin/bash
SESSION_ID="7f08a8f6-b90c-47ac-bc1b-31943c7b995a"
AGENT_ID=$(jq -r 'select(.toolUseResult.agentId) | .toolUseResult.agentId' /home/node/.config/projects/-workspace/${SESSION_ID}.jsonl 2>/dev/null | tail -1)
echo "$AGENT_ID" > /tmp/agent-id.txt
EOF
bash /tmp/extract-agent-id.sh

Example 3: Multiple Parameter Expansions

❌ Fails with parse error:

bash
PROJECT="my-project"
SUBDIR="src/main"
TARGET="/workspace/${PROJECT}/${SUBDIR}/code"
mkdir -p "$TARGET"
cd "$TARGET" && git status

✅ Correct (converted):

bash
cat > /tmp/setup-dir.sh << 'EOF'
#!/bin/bash
PROJECT="my-project"
SUBDIR="src/main"
TARGET="/workspace/${PROJECT}/${SUBDIR}/code"
mkdir -p "$TARGET"
cd "$TARGET" && git status
EOF
bash /tmp/setup-dir.sh

When NOT to Use Script File

Some bash commands work fine directly in Bash tool:

✅ Simple commands (no conversion needed):

bash
# Simple variable substitution
NAME="test"
echo "Hello $NAME"

# Basic command substitution
FILES=$(ls *.txt)
echo "$FILES"

# Simple paths
cd /workspace/main && pwd

# Git commands
git status
git log --oneline -5

Error Messages to Watch For

If you see these errors, use this skill:

  • •(eval):1: parse error near '('
  • •(eval):1: command not found: (eval)
  • •syntax error near unexpected token
  • •bad substitution

Integration with Existing Workflows

optimize-doc command: Already documented with script file requirement for validation ID extraction

Other skills/commands: Use this skill proactively when commands match the problematic patterns above

Best Practices

  1. •Name script files descriptively: Use /tmp/<descriptive-name>.sh instead of generic names
  2. •Add error handling: Include set -euo pipefail and trap for better debugging
  3. •Clean up: Remove script files after use if they're not needed for debugging
  4. •Document: Add comment in script explaining what it does
  5. •Test: Verify script works before using in production workflows

Quick Reference Card

Need script file if command has:

  • •✓ ${VAR##pattern} or ${VAR%%pattern}
  • •✓ Complex $(...) with pipes and filters
  • •✓ Multiple ${VAR} expansions in one line
  • •✓ Nested quotes with variables
  • •✓ Parse error mentioning (eval):1

Don't need script file if:

  • •✗ Simple $VAR or ${VAR}
  • •✗ Basic $(command)
  • •✗ No error reported
  • •✗ Simple single-line commands

Output Format

When skill is invoked, it outputs:

bash
# Converted command (ready to execute):
cat > /tmp/<generated-name>.sh << 'EOF'
#!/bin/bash
set -euo pipefail

<your original command converted>

EOF
bash /tmp/<generated-name>.sh

Simply copy and paste this into the Bash tool to execute.

Related Documentation

  • •CLAUDE.md § Tool Usage Best Practices § Bash Tool - Path Handling § Parameter Expansion Limitation
  • •optimize-doc command (documents script file requirement)

Maintenance

This skill should be updated when:

  • •New problematic bash patterns are discovered
  • •Bash tool behavior changes
  • •Better conversion approaches are found
  • •Additional error patterns are identified