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Published: Nov 21, 2016 License: Apache-2.0 Imports: 4 Imported by: 3



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Nash is a system shell, inspired by plan9 rc, that makes it easy to create reliable and safe scripts taking advantages of operating systems namespaces (on linux and plan9) in an idiomatic way.

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Useful stuff

  • nashfmt: Formats nash code (like gofmt) but no code styling defined yet.
  • nashcomplete: Autocomplete done in nash script.
  • Dotnash: Nash profile customizations (e.g: prompt, aliases, etc)
  • nash-mode: Emacs major mode integrated with nashfmt.

Why nash scripts are reliable?

  1. Nash aborts at first non-success status of commands;
  2. Nash aborts at first unbound variable;
  3. It's possible to check the result status of every component of a pipe;
  4. no eval;
  5. Strings are pure strings (no evaluation of variables);
  6. No wildcards (globbing) of files; ('rm *' removes a file called '*');
  7. No obscure syntax;
  8. Support tooling for indent/format and statically analyze the scripts;


If you have Go, go-get it:

# Make sure GOPATH/bin is in your PATH
go get

If not, download the latest binary release and copy to somewhere in your PATH.

Getting started

Nash syntax resembles a common shell:

λ> echo "hello world"
hello world

Pipes works like borne shell and derivations:

λ> cat spec.ebnf | wc -l

Output redirection works like Plan9 rc, but not only for filenames. It supports output redirection to tcp, udp and unix network protocols.

# stdout to log.out, stderr to log.err
λ> ./daemon >[1] log.out >[2] log.err
# stderr pointing to stdout
λ> ./daemon-logall >[2=1]
# stdout to /dev/null
λ> ./daemon-quiet >[1=]
# stdout and stderr to tcp address
λ> ./daemon >[1] "udp://syslog:6666" >[2=1]
# stdout to unix file
λ> ./daemon >[1] "unix:///tmp/syslog.sock"

For safety, there's no eval or string/tilde expansion or command substitution in Nash.

To assign command output to a variable exists the '<=' operator. See the example below:

fullpath <= realpath $path | xargs -n echo
echo $fullpath

The symbol '<=' redirects the stdout of the command or function invocation in the right-hand side to the variable name specified.

If you want the command output splited into an array, then you'll need to store it in a temporary variable and then use the builtin split function.

out <= find .
files <= split($out, "\n")

for f in $files {
        echo "File: " + $f

To avoid problems with spaces in variables being passed as multiple arguments to commands, nash pass the contents of each variable as a single argument to the command. It works like enclosing every variable with quotes before executing the command. Then the following example do the right thing:

fullname = "John Nash"
./ci-register --name $fullname --option somevalue

On bash you need to enclose the $fullname variable in quotes to avoid problems.

Nash syntax does not support shell expansion from strings. There's no way to do things like the following in nash:

echo "The date is: $(date +%D)" # DOESNT WORKS!

Instead you need to assign each command output to a proper variable and then concat it with another string when needed. In nash, the example above must be something like that:

today <= date "+%D"
echo "The date is: " + $today

The concat operator (+) could be used between variables and literal strings.

Functions can be declared with "fn" keyword:

fn cd(path) {
    fullpath <= realpath $path | xargs echo -n
    PROMPT="[" + $fullpath + "]> "
    setenv PROMPT

And can be invoked as a normal function invocation:

λ> cd("/etc")

Functions are commonly used for nash libraries, but when needed it can be bind'ed to some command name. Using the cd function below, we can override the builtin cd with that command with bindfn statement.

λ> # bindfn syntax is:
λ> # bindfn <function-name> <cmd-name>
λ> bindfn cd cd
λ> cd /var/log

The only control statements available are if, else and for. In the same way, nash doesn't support shell expansion at if condition. For check if a directory exists you must use:

-test -d $rootfsDir    # if you forget '-', the script will be aborted here
                       # if path not exists

if $status != "0" {
        echo "RootFS does not exists."
        exit $status

Nash stops executing the script at first error found and, in the majority of times, it is what you want (specially for deploys). But Commands have an explicitly way to bypass such restriction by prepending a dash '-' to the command statement. For example:

fn cleanup()
        -rm -rf $buildDir
        -rm -rf $tmpDir

The dash '-' works only for operating system commands, other kind of errors are impossible to bypass. For example, trying to evaluate an unbound variable aborts the program with error.

λ> echo $PATH
λ> echo $bleh
ERROR: Variable '$bleh' not set

Long commands can be splited in multiple lines:

λ> (aws ec2 attach-internet-gateway	--internet-gateway-id $igwid
									--vpc-id $vpcid)

λ> instanceId <= (
	aws ec2 run-instances
			--image-id ami-xxxxxxxx
			--count 1
			--instance-type t1.micro
			--key-name MyKeyPair
			--security-groups my-sg
    | jq ".Instances[0].InstanceId"
λ> echo $instanceId

Namespace features

Nash is built with namespace support only on Linux (Plan9 soon). If you use OSX, BSD or Windows, then the rfork keyword will fail.

The examples below assume you are on a Linux box.

Below are some facilities for namespace management inside nash. Make sure you have USER namespaces enabled in your kernel:

zgrep CONFIG_USER_NS /proc/config.gz

If it's not enabled you will need root privileges to execute every example below...

Creating a new process in a new USER namespace (u):

λ> id
uid=1000(user) gid=1000(user) groups=1000(user),98(qubes)
λ> rfork u {
uid=0(root) gid=0(root) groups=0(root),65534

Yes, Linux supports creation of containers by unprivileged users. Tell this to the customer success of your container-infrastructure-vendor. :-)

The default UID mapping is: Current UID (getuid) => 0 (no range support). I'll look into more options for this in the future.

Yes, you can create multiple nested user namespaces. But kernel limits the number of nested user namespace clones to 32.

λ> rfork u {
    echo "inside first container"


    rfork u {
        echo "inside second namespace..."


You can verify that other types of namespace still requires root capabilities, see for PID namespaces (p).

λ> rfork p {
ERROR: fork/exec ./nash: operation not permitted

The same happens for mount (m), ipc (i) and uts (s) if used without user namespace (u) flag.

The c flag stands for "container" and is an alias for upmnis (all types of namespaces). If you want another shell (maybe bash) inside the namespace:

λ> rfork c {
[root@stay-away nash]# id
uid=0(root) gid=0(root) groups=0(root),65534
[root@stay-away nash]# mount -t proc proc /proc
[root@stay-away nash]#
[root@stay-away nash]# ps aux
root         1  0.0  0.0  34648  2748 pts/4    Sl   17:32   0:00 -rcd- -addr /tmp/nash.qNQa.sock
root         5  0.0  0.0  16028  3840 pts/4    S    17:32   0:00 /usr/bin/bash
root        23  0.0  0.0  34436  3056 pts/4    R+   17:34   0:00 ps aux

Everything except the rfork is like a common shell. Rfork will spawn a new process with the namespace flags and executes the commands inside the block on this namespace. It has the form:

rfork <flags> {
    <statements to run inside the container>

OK, but how scripts should look like?

See the project nash-app-example.

Didn't work?

I've tested in the following environments:

Linux 4.7-rc7

Linux 4.5.5 (amd64)

Linux 4.3.3 (amd64)

Linux 4.1.13 (amd64)
Fedora release 23

Linux 4.1.13 (amd64)
Debian 8

Language specification

The specification isn't complete yet, but can be found here. The file spec_test.go makes sure it is sane.

Some Bash comparisons

Bash Nash Description
GOPATH=/home/user/gopath GOPATH="/home/user/gopath" Nash enforces quoted strings
GOPATH="$HOME/gopath" GOPATH=$HOME+"/gopath" Nash doesn't do string expansion
export PATH=/usr/bin PATH="/usr/bin"
setenv PATH
setenv operates only on valid variables
export showenv
ls -la ls -la Simple commads are identical
ls -la "$GOPATH" ls -la $GOPATH Nash variables shouldn't be enclosed in quotes, because it's default behaviour
./worker 2>log.err 1>log.out ./worker >[2] log.err >[1] log.out Nash redirection works like plan9 rc
./worker 2>&1 ./worker >[2=1] Redirection map only works for standard file descriptors (0,1,2)


The PID 1 of every namespace created by nash is the same nash binary reading commands from the parent shell via unix socket. It allows the parent namespace (the script that creates the namespace) to issue commands inside the child namespace. In the current implementation the unix socket communication is not secure yet.


Nowadays everyone agrees that a good deploy requires containers, but why this kind of tools (docker, rkt, etc) and libraries (lxc, libcontainer, etc) are so bloated and magical?

In the past, the UNIX sysadmin had the complete understanding of the operating system and the software being deployed. All of the operating system packages/libraries going to production and the required network configurations in every machine was maintained by several (sometimes un-mantainable) scripts. Today we know that this approach have lots of problems and the container approach is a better alternative. But in the other end, we're paying a high cost for the lose of control. The container-technologies in the market are very unsafe and few people are worrying about. No one knows for hundred percent sure, how the things really works because after every release it's done differently. On my view it's getting worse and worse...

Before Linux namespace, BSD Jails, Solaris Zones, and so on, the sysadmin had to fight the global view of the operating system. There was only one root mount table, only one view of devices and processes, and so on. It was a mess. This approach then proved to be much harder to scale because of the services conflicts (port numbers, files on disk, resource exhaustion, etc) in the global OS interface. The container/namespace idea creates an abstraction to the process in a way that it thinks it's the only process running (not counting init), it is the root (or no) and then, the filesystem of the container only has the files required for it (nothing more).

What's missing is a safe and robust shell for natural usage of namespace/container ideas for everyone (programmers, sysadmins, etc).

Nash is a way for you, that understand the game rules, to make reliable deploy scripts using the good parts of the container technologies. If you are a programmer, you can use a good language to automate the devops instead of relying on lots of different technologies (docker, rkt, k8s, mesos, terraform, and so on). And you can create libraries for code-reuse.

It's only a simple shell plus a keyword called rfork. Rfork try to mimic what Plan9 rfork does for namespaces, but with linux limitations in mind.


I needed to create test scripts to be running on different mount namespaces for testing a file server and various use cases. Using bash in addition to docker or rkt was not so good for various reasons. First, docker prior to version 1.10 doesn't support user namespaces, and then my make test would requires root privileges, but for docker 1.10 user namespace works still requires to it being enabled in the daemon flags (--userns-remap=?) making more hard to work on standard CIs (travis, circle, etc)... Another problem was that it was hard to maintain a script, that spawn docker containers inheriting environment variables from parent namespace (or host). Docker treats the container as a different machine or VM, even calling the parent namespace as "host". This breaks the namespace sharing/unsharing idea of processes. What I wanted was a copy of the missing plan9 'environment namespace' to child namespaces.

Want to contribute?

Open issues and PR :) The project is in an early stage, be patient because things can change in the future.

"What I cannot create, I do not understand."

-- Richard Feynman



Package nash provides a library to embed the `nash` scripting language within your program or create your own nash cli.

package main

import (

func main() {
	nash, err := nash.New()

	if err != nil {

	// Execute a script from string
	err = nash.ExecuteString("-input-", `echo Hello World`)

	if err != nil {


Hello World




This section is empty.


This section is empty.


This section is empty.


type Shell

type Shell struct {
	// contains filtered or unexported fields

Shell is the execution engine of the scripting language.

func New

func New() (*Shell, error)

New creates a new `nash.Shell` instance.

func (*Shell) DotDir

func (nash *Shell) DotDir() string

DotDir returns the value of the NASHPATH environment variable

func (*Shell) Environ

func (nash *Shell) Environ() shell.Env

Environ returns the set of environment variables in the shell

func (*Shell) Exec

func (nash *Shell) Exec(path, content string) error

Exec executes the code specified by string content. By default, nash uses os.Stdin, os.Stdout and os.Stderr as input, output and error file descriptors. You can change it with SetStdin, SetStdout and Stderr, respectively. The path is only used for error line reporting. If content represents a file, then setting path to this filename should improve debugging (or no).

func (*Shell) ExecFile

func (nash *Shell) ExecFile(path string) error

ExecFile executes the script content of the file specified by path. See Exec for more information.

func (*Shell) ExecTree

func (nash *Shell) ExecTree(tree *ast.Tree) (sh.Obj, error)

ExecTree evaluates the given abstract syntax tree. it returns the object result of eval or nil when not applied and error.

func (*Shell) ExecuteFile deprecated

This method has been deprecated.
func (nash *Shell) ExecuteFile(path string) error

ExecuteFile executes the given file. Deprecated: Use ExecFile instead.

func (*Shell) ExecuteString deprecated

This method has been deprecated.
func (nash *Shell) ExecuteString(path, content string) error

ExecuteString executes the script content. Deprecated: Use Exec instead.

func (*Shell) ExecuteTree deprecated

This method has been deprecated.
func (nash *Shell) ExecuteTree(tr *ast.Tree) (sh.Obj, error)

ExecuteTree executes the given tree. Deprecated: Use ExecTree instead.

func (*Shell) GetFn

func (nash *Shell) GetFn(name string) (sh.Fn, bool)

GetFn gets the function object.

func (*Shell) Getvar

func (nash *Shell) Getvar(name string) (sh.Obj, bool)

Getvar retrieves a variable from nash session

func (*Shell) Prompt

func (nash *Shell) Prompt() string

Prompt returns the environment prompt or the default one

func (*Shell) SetDebug

func (nash *Shell) SetDebug(b bool)

SetDebug enable some logging for debug purposes.

func (*Shell) SetDotDir

func (nash *Shell) SetDotDir(path string)

SetDotDir sets the NASHPATH environment variable. The NASHPATH variable points to the location where nash will lookup for the init script and libraries installed.

func (*Shell) SetNashdPath

func (nash *Shell) SetNashdPath(path string)

SetNashdPath sets an alternativa path to nashd

func (*Shell) SetStderr

func (nash *Shell) SetStderr(err io.Writer)

SetStderr set the stderr of nash engine

func (*Shell) SetStdin

func (nash *Shell) SetStdin(in io.Reader)

SetStdin set the stdin of the nash engine

func (*Shell) SetStdout

func (nash *Shell) SetStdout(out io.Writer)

SetStdout set the stdout of the nash engine.

func (*Shell) Setvar

func (nash *Shell) Setvar(name string, value sh.Obj)

Setvar sets or updates the variable in the nash session

func (*Shell) Stderr

func (nash *Shell) Stderr() io.Writer

func (*Shell) Stdin

func (nash *Shell) Stdin() io.Reader

func (*Shell) Stdout

func (nash *Shell) Stdout() io.Writer

Source Files


Path Synopsis
Package main has two sides: - User mode: shell - tool mode: unix socket server for handling namespace operations When started, the program choses their side based on the argv[0].
Package main has two sides: - User mode: shell - tool mode: unix socket server for handling namespace operations When started, the program choses their side based on the argv[0].
Package scanner is the lexical parser.
Package scanner is the lexical parser.
nash provides the execution engine
nash provides the execution engine

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