Known Limitations

fortsh has some limitations compared to bash and other shells.

Platform Limitations

macOS Apple Silicon (M1/M2/M3)

Command line limit: 127 characters

Due to a bug in flang-new (the only working Fortran compiler on ARM64 macOS), string operations are limited to 128 bytes.

Workarounds:

• Use aliases for long commands
• Use variables for long paths
• Save complex one-liners as scripts

See macOS Apple Silicon for details.

macOS Intel

No significant limitations. Full functionality available.

Linux

No significant limitations. This is the primary development platform.

Feature Limitations

Nested Brace Expansion

Complex nested brace expansions may not work:

# Works
echo {a,b}{1,2}           # a1 a2 b1 b2

# May not work
echo {{a,b},{c,d}}        # Nested braces

Vi Mode Gaps

Vi editing mode is functional but incomplete compared to bash:

• Some vi commands not implemented
• Some movement commands may differ
• Visual mode not supported

Arithmetic Precision

Shell arithmetic uses Fortran integers:

echo $((2**62))           # Works
echo $((2**63))           # May overflow

For arbitrary precision, use external tools like bc.

Process Substitution

Process substitution is supported but may have edge cases:

diff <(cmd1) <(cmd2)      # Works

Coprocess

Coproc is not implemented:

coproc cmd                # Not supported

Compatibility Notes

Bash Compatibility

fortsh aims for ~99% bash compatibility. Known differences:

POSIX Compliance

fortsh passes POSIX compliance tests (3,776 tests). Some extensions may differ from strict POSIX.

shopt Options

Not all bash shopt options are supported:

# Supported
shopt -s nullglob
shopt -s extglob

# May not be supported
shopt -s globstar       # Check documentation

Resource Limits

Maximum Values

Performance

fortsh may be slower than bash on:

• Very large scripts (thousands of lines)
• Heavy process spawning
• Complex string manipulation

For most interactive use and moderate scripts, performance is comparable.

Reporting Issues

If you encounter a limitation that should be fixed:

1. Check if it's a known issue on GitHub
2. Open an issue with a minimal reproduction case
3. Include:
   • fortsh version (fortsh --version)
   • Platform (uname -a)
   • Expected vs actual behavior

GitHub: github.com/fortrangoingonforty/fortsh/issues

Future Improvements

Planned improvements:

• Increased associative array limits
• More vi mode commands
• Better nested brace expansion
• Resolution of Apple Silicon limitation (pending compiler fixes)

The project welcomes contributions for any of these areas.