fs.bash() - Mesa Docs

fs.bash(...) builds a just-bash interpreter rooted at the mounted filesystem. Commands run against MesaFS; no host shell is spawned.

const bash = fs.bash({ cwd: '/acme/app', env: { CI: 'true' } });
const result = await bash.exec('rg -n TODO src | head -20');

console.log(result.exitCode);
console.log(result.stdout);
console.log(result.stderr);

Options

Record<string, string> | undefined

Environment variables for the shell. The host process environment is not inherited unless you pass it explicitly.

string | undefined

Working directory inside the mount. Defaults to /.

object | undefined

Limits for command count, loops, output sizes, and related execution safety controls.

CommandName[] | undefined

Restrict available built-in command names.

Record<string, CustomCommand> | undefined

NetworkConfig | undefined

Enable network commands with explicit URL policy.

SecureFetch | undefined

Custom secure fetch implementation used by network-enabled commands.

object | undefined

Python execution configuration. Disabled by default.

object | undefined

JavaScript execution configuration. Disabled by default.

BashLogger | undefined

Receives command execution logs.

exec()

exec(command) takes one string containing one or more shell statements.

const result = await bash.exec(`
rg -l integration .
node --test
`);

string

required

Shell script to execute.

Response

exec(...) returns ExecResult from just-bash.

string

Standard output.

string

Standard error.

number

Process exit code. 0 indicates success.

Record<string, string>

Resulting shell environment when included by just-bash.

Command failures

Command failures usually return a non-zero exitCode; they do not automatically raise.

const result = await bash.exec('cat /acme/app/missing.txt');
if (result.exitCode !== 0) {
  console.error(result.stderr);
}

Binary files

Use fs.readFileBuffer(...) for binary files. Text-oriented shell commands such as cat are intended for text output.

​Options

​exec()

​Response

​Command failures

​Binary files

Options

exec()

Response

Command failures

Binary files