posh

README

posh

A portable Unix-like command shell for Windows, written in Go — similar in spirit to GNU bash.

posh runs interactively with full line-editing and persistent history, executes shell scripts, and provides the core shell primitives you expect: pipelines, redirections, variable expansion, command substitution, arithmetic expansion, glob expansion, background jobs, and a set of built-in commands.

The binary name is derived from the executable stem — rename it and all prompts update automatically.

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Installation

Download binary (easiest)

Grab the latest pre-built binary from the Releases page — no Go required.

File	Platform
posh.exe	Windows (amd64)
posh-linux-amd64	Linux (amd64)

Place it somewhere on your PATH and you're done. On Linux, mark it executable first:

chmod +x posh-linux-amd64
mv posh-linux-amd64 ~/.local/bin/posh

go install

Requires Go 1.21+.

go install github.com/fermat-tech/posh@latest

The binary lands in %USERPROFILE%\go\bin (Windows) or ~/go/bin (Linux/macOS), which should already be on your PATH.

Build from source

git clone https://github.com/fermat-tech/posh.git
cd posh
go build -o posh.exe .   # Windows
go build -o posh .       # Linux / macOS

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Usage

posh                   Interactive REPL
posh script.posh       Execute a script file
posh -c "command"      Run a single command and exit

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Features (Phase 1)

Pipelines

ls | wc -l
cat file.txt | grep foo | sort

Redirections

echo hello > out.txt
cat >> log.txt
sort < input.txt
cmd 2> errors.txt
cmd &> all.txt        # stdout + stderr

Variables

NAME=world
echo Hello $NAME
echo "Hello ${NAME}"
echo $?               # last exit code
echo $$               # current PID

Command substitution

echo "Today is $(date)"
FILES=$(ls *.go)

Arithmetic expansion

echo $((2 + 3 * 4))
SIZE=$((1024 * 1024))

Glob expansion

echo *.go
ls src/**/*.txt

Tilde expansion

cd ~
cat ~/notes.txt

Logical operators and sequences

make && echo "Build OK"
test -f file || echo "Not found"
cd /tmp; ls; cd -

Background jobs

long-running-command &
jobs

Subshells

(cd /tmp && ls)

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Built-in commands

Command	Description
cd [dir]	Change directory (default: $HOME)
pwd	Print working directory
echo [-n] [args]	Print arguments
printf fmt [args]	Formatted output
export [VAR[=val]]	Export variable to child processes
unset VAR...	Remove variable
env	Print exported environment
set [VAR=val]	Set or list shell variables
source FILE / . FILE	Execute file in current shell context
alias [name[=val]]	Define or list aliases
unalias name...	Remove aliases
history	Show command history
type name...	Show whether name is a builtin, alias, or external
jobs	List background jobs
true / false / :	Exit 0 / exit 1 / no-op
help	Show built-in help
exit [n]	Exit with status n

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Startup file

posh sources ~/.poshrc on interactive startup.

# ~/.poshrc
alias ll='ls -la'
export EDITOR=notepad
PS1='\u@\h \w \$ '

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Prompt (PS1)

Escape	Meaning
\u	Current username
\h	Short hostname
\H	Full hostname
\w	Working directory (~ abbreviated)
\W	Basename of working directory
\$	$ for normal users, # for root
\n	Newline
\\	Literal backslash

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Line editing (interactive mode)

Key	Action
Up / Down	Navigate history
Ctrl+R	Reverse history search
Ctrl+C	Interrupt (return to prompt)
Ctrl+D	Exit on empty line
Tab	Filename completion

History is saved to ~/.posh_history (max 1000 entries).

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Command lookup

On Windows, posh respects PATHEXT when looking up commands — it will find .EXE, .CMD, .BAT, .PS1, and any other extension listed in PATHEXT.

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Color

Color in the prompt follows NO_COLOR (see no-color.org). Set NO_COLOR=1 to disable.

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License

MIT