posh

posh [+-aCefilnuvx] [+-o option] [[-c command-string [command-name] | -s | file] [argument...]]

posh (Policy-compliant Ordinary SHell) is a reimplementation of the Bourne shell derived from pdksh, designed to comply strictly with the POSIX/SUSv3 specification and Debian policy. It intentionally excludes extensions beyond the POSIX standard, making it useful for testing script portability.Scripts that run correctly under posh are more likely to be portable across different Unix-like environments. Running a script under posh acts as a conformance check: if bash-specific features are used, posh will reject them, revealing portability issues before deployment on a minimal system.Posh supports standard shell features including parameter substitution, command substitution, arithmetic expressions, pipelines, file globbing, here-documents, and job control in interactive sessions.

-c command

Execute commands from the given string

Force interactive mode and enable job control

Behave as a login shell, reading profile files

Read commands but do not execute (syntax check only)

Read commands from standard input; treat remaining arguments as positional parameters

Privileged mode: read `/etc/suid_profile` instead of the user profile

Exit immediately if a command exits with a non-zero status

Treat unset variables as an error when substituting

Print input lines to stderr as they are read

Print each command and its arguments to stderr before execution (trace mode)

Export all variables that are assigned or modified

Posh deliberately omits many common bash extensions: arrays, process substitution (`<()`), `[[ ]]` compound tests, `local` declarations, and various other bashisms. Scripts relying on these features must be rewritten for posh compatibility. The shell is not intended as a daily interactive shell but as a portability testing tool.

posh was created by Clint Adams for the Debian project to provide a shell strictly conforming to POSIX and the Debian Policy Manual requirements. It is derived from pdksh (Public Domain Korn Shell), originally written by Eric Gisin in the 1980s as a free Korn shell implementation.

sh(1), bash(1), dash(1), ksh(1)

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