posixsh

README

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.