/posixsh

Experimental POSIX shell implementation

Primary LanguageShellBSD 2-Clause "Simplified" LicenseBSD-2-Clause

This is xiaq's experimental POSIX shell. If it works out, it will eventually to be integrated into Elvish.

License is BSD 2-clause.

Files in spec/oil are derived from the Oil, licensed under Apache License 2.0. See spec/oil/LICENSE.

Status and limitations

The majority of POSIX shell features are implemented.

The following features are currently missing:

  • Closing FDs in redirections (<&-, 2.7.5, 2.7.6)
  • Background jobs and related features
    • All of 2.9.3 "Async lists"
    • $!
    • bg
    • fg
    • jobs
    • wait
    • set -o monitor (set -m)
    • set -o notify (set -n)
  • set -o errexit (set -e)
  • set -o noexec (set -n)
  • exec
  • getopts
  • hash
  • $LINENO (2.5.3)
  • Signal handling
    • All of 2.11 "Signals and error handling"
    • trap
  • Interactive features
    • $ENV (2.5.3)
    • $PS1 (2.5.3)
    • $PS2 (2.5.3)
    • $PS4 (2.5.3)
    • fc
    • set -o ignoreeof
    • set -o nolog.

Some implemented features are incomplete:

  • In <<- heredocs, leading tabs in expansions are not stripped (2.7.4). Example:

    cat <<-EOF
  $(echo '
  bar')
EOF

    This should print an empty line followed by a line of just bar, but currently this implementation has a tab before the bar.

  • Argument of variable expansions may not contain whitespaces (2.6.2). Example:

    echo ${x=foo  bar}

    This should print foo bar (with one space) and assign $x to foo bar (with two spaces). This implementation treats this as a syntax error now.

Since Go doesn't support fork, subshells are run in the same process, with their own virtualized working directories and variables. This approach has some inherent limitations:

  • Some properties cannot be virtualized: ulimit, umask and exec (when implemented) will affect the entire process.

  • Code that actually depends on subshells running in separate processes won't work correctly.

The following features are out of scope and will likely never be implemented:

  • set -h.

  • kill and newgrp - both are widely available as standalone commands.

  • Internationalization/localization. This includes support for $LANG, $LC_* and $NLSPATH.