Installation and the Command Line

MushScript programs are compiled and run by the mush command-line tool; confirm it is on your PATH and you are ready to start.

Checking Availability


$ mush --version
mush 0.5.2

If the command prints a version number, the environment is usable. How to obtain mush, and which versions ship through which release channels, is outside the scope of this manual.

Command Summary

Command	Effect
`mush`	Interactive REPL
`mush <file.ms>`	Run a script (equivalent to `mush run <file.ms>`)
`mush run [file.ms]`	Compile and run; with the file omitted, runs the entry declared in `package.msd`
`mush -`	Read a script from stdin and run it
`mush -e "<code>"`	One-shot evaluation; the expression result is echoed
`mush check [path...]`	Compile and report diagnostics only; nothing executes
`mush fmt [path...] [--check]`	Format; `--check` only reports differences without touching files
`mush test [paths...]`	Run `.ms` tests
`mush --version` / `--help`	Version and help

Target Resolution for run and check

run and check resolve their target in three forms:

Target omitted: discover package.msd upward from the current directory; if none is found, treat the current directory as the package root and collect every .ms file.
A .ms file: compile the package that file belongs to.
A directory: treat the directory as a package root and collect it.

On success check prints a one-line summary: the name in the summary is the package name (the file name in the single-file case), followed by the number of source files checked. When there are warnings the line becomes “N warnings”, and the full warning text is printed above the summary.


$ mush check helloworld.ms
Checked helloworld (1 source file): no errors
$ mush run helloworld.ms
Hello, world

Use check when changing code to hunt down a problem, and run to confirm behavior.

Exit Codes

Code	Meaning
0	Success
1	Compilation or run failure
2	Usage error
130	Interrupted by Ctrl+C

Notes

A program that fails to compile never executes; runtime output always comes from a program that passed the full compilation.
.ms files must be UTF-8 encoded.
In command-line examples, $ is the shell prompt, not part of the input.
For the full rules on script arguments (including the -- separator), see the main and exit codes page.

Last updated on October 11, 2026