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Bash Syntax Support in MyCE

This guide documents the bash syntaxes that MyCE supports when parsing command definitions from .myCommands files.

Note

This document was generated with AI assistance and may contain inaccuracies or errors. Please verify examples against the actual MyCE source and test suite and report any discrepancies found.

Supported Bash Syntaxes

1. Command Substitution with Dollar-Parentheses

Syntax: $(command)

Examples:

# Simple command substitution in path
buildPath=$(echo /build)/system

# Nested command substitutions
version=$(echo $(git describe --tags))

# Command substitution with arguments
installer=$(find . -name install.sh)

# Multiple uses in single command
report=echo "Built by $(whoami) in $(pwd)"

2. Backtick Command Substitution (Legacy)

Syntax: `command`

Examples:

# Legacy backtick syntax (still supported)
binPath=`echo /usr/bin`/echo

# Multiple backtick substitutions
timestamp=echo "Started at `date` in `pwd`"

Note

Backticks in .myCommands files may be evaluated by bash during file sourcing. Prefer $(...) syntax for better compatibility.

3. Single Quoted Strings

Syntax: '...'

Everything inside single quotes is treated literally—no variable expansion, no command substitution, no escaping.

Examples:

# Preserve literal dollar signs and variables
display=echo 'Price is $100 and VAR=$VAR'

# Preserve spaces without escaping
message=echo 'This is a multi word string'

# Combine with other syntaxes
combine=echo 'Literal' $(date)

4. Double Quoted Strings

Syntax: "..."

Double quotes allow variable expansion and command substitution, but protect spaces and most special characters.

Examples:

# Variables and command substitution work inside double quotes
display=echo "File created at $(date) by $USER"

# Spaces are preserved inside double quotes
message=echo "Multi word string stays intact"

# Combining with unquoted parts
full=echo "Start" middle "End"

5. Process Substitution (Input Form)

Syntax: <(command)

Provides input from a command's output.

Examples:

# Read from process substitution
compare=diff <(sort file1) <(sort file2)

# Use in pipe
analyze=cat <(echo "header") myfile

# Multiple process substitutions
merge=paste <(seq 1 10) <(seq 11 20)

6. Process Substitution (Output Form)

Syntax: >(command)

Sends output to a command's input.

Examples:

# Write to process substitution
tee_copy=tee >(cat > backup.txt)

# Log output while filtering
tee_filter=tee >(grep ERROR > errors.log)

# Multiple outputs
split_output=tee >(cat > file1) >(cat > file2)

7. Escaped Spaces

Syntax: \ (backslash-space)

A backslash escapes the next character, allowing spaces to be included in a single word without quoting.

Examples:

# Escaped space in command argument
space_cmd=echo hello\ world

# Useful in file paths
run=echo /path/to\ dir/with\ spaces/script

# Can combine with quotes
mixed=echo 'quoted' unquoted\ space quoted

8. Parameter Expansion

Syntax: ${VAR}, ${VAR:-default}, ${VAR:offset}, ${VAR#pattern}, etc.

Parameter expansion provides variable references with optional default values, substring extraction, and pattern removal.

Examples:

# Basic variable reference
path=echo ${HOME}/projects

# Default values
config=echo ${CONFIG_FILE:-/etc/default.conf}

# Substring operations
truncate=echo ${LONG_VAR:0:10}

# Pattern removal (trailing)
strip=echo ${PATH%:/usr/bin}

# Nested expansions
complex=echo ${FINAL_PATH#${PREFIX}/}

9. Mixed Syntax Combinations

You can freely combine any of the above syntaxes.

Examples:

# Mixed quotes and substitution
report=echo "Report generated on $(date) in $(pwd)"

# Escaped space with quotes
file=echo 'file\ name' "/escaped\ path"

# Nested and combined
complex=cat <(echo "Header") "$(dirname $0)/data.txt" output\ file

# Multiple substitution forms
multi=$(dirname $1)\ $(basename $2)

Comprehensive Test Suite

MyCE includes 18 regression tests covering all supported bash syntaxes:

Core Syntax Tests

  • subshell.subshellPath - Command substitution $(...)
  • subshell.backtickPath - Backtick substitution `...`
  • subshell.quotedArg - Double-quoted arguments with spaces
  • subshell.singleQuotedArg - Single-quoted literal preservation
  • subshell.processSub - Process substitution input <(...)
  • subshell.complexExpansion - Parameter expansion with special characters

Edge Case Tests

  • subshell.processSubOut - Process substitution output >(...)
  • subshell.escapedSpace - Escaped spaces in command arguments
  • subshell.nestedSub - Nested command substitution
  • subshell.mixedQuotes - Single and double quotes together
  • subshell.quotedWithSub - Command substitution inside double quotes
  • subshell.paramDefault - Parameter expansion with default value
  • subshell.paramSubstr - Parameter substring extraction
  • subshell.paramPattern - Pattern removal in parameter expansion
  • subshell.multiSub - Multiple consecutive substitutions in one word
  • subshell.subWithSpaces - Spaces in substitution output preserved
  • subshell.escapedDollar - Literal dollar sign with single quotes

Common Usage Patterns

Complex Command Paths

Use command substitution to compute executable paths dynamically:

# Path from variable
install=$(which npm)/npm-install

# Path from git repository
gitutil=$(git rev-parse --show-toplevel)/bin/util

Commands with Conditional Output

Combine process substitution with comparison tools:

# Compare sorted outputs
diff_sorted=diff <(sort "$1") <(sort "$2")

# Filter and process
parse=grep pattern <(command)

Multi-Step Processing

Chain multiple substitutions for complex workflows:

# Extract, format, and display
report=echo "Report for $(whoami) at $(date)" | tee >(mail admin)

Template Commands

Use parameter expansion with defaults for flexible command templates:

# Port defaults to 8080 if not specified
server=node server.js --port ${PORT:-8080}

# Config path with fallback
deploy=./deploy.sh --config ${CONFIG_FILE:-/etc/deploy.conf}

Tips and Best Practices

  1. Prefer $(...) over backticks - More readable and nests better
  2. Quote command arguments - Use "..." when arguments contain spaces
  3. Use single quotes for literal values - Prevents accidental expansion
  4. Escape special characters - Use \$ for literal dollar signs
  5. Test complex commands - Use my command ? to preview before execution
  6. Document with descriptions - Add # description: comments for clarity

Example:

# description: Compile with optimization flags
build=$(find . -name Makefile)/Makefile \
  && make -f "$1" CFLAGS="${CFLAGS:-O2}"

Further Reading

  • See README.md for general MyCE features
  • Check CHANGE_HISTORY.md for implementation details
  • Review test cases in /test/test_cases/command_substitution.py for comprehensive examples