exec

Builtin index · File I/O

result = exec(program, [args], [shell=], [cwd=], [stdin=])

Input: program, args, shell, cwd, stdin · Output: result

What it is

Runs program (a Str) and waits, capturing what it printed. args is an optional List of arguments passed to the OS as separate items — not joined into a command line and re-split — so a path with a space in it needs no quoting rule. shell=true instead reads program as a whole command line for cmd /C (Windows) or sh -c, so pipes and && work. cwd= (a Str) runs it in that directory without moving the caller. stdin= (a Str) is written to the program's input, which is then closed, so a program reading to EOF gets exactly that and does not hang.

Overloads

One call shape — this function is not overloaded.

Code	Input	Output	Description
`result = exec(program, [args], [shell=], [cwd=], [stdin=])`	`program` StrRuns `program` (a `Str`) and waits, capturing what it printed. `args` List, optional`args` is an optional `List` of arguments passed to the OS as separate items — not joined into a command line and re-split — so a path with a space in it needs no quoting rule. `shell` optional`shell=true` instead reads `program` as a whole command line for `cmd /C` (Windows) or `sh -c`, so pipes and `&&` work. `cwd` Str, optional`cwd=` (a `Str`) runs it in that directory without moving the caller. `stdin` Str, optional`stdin=` (a `Str`) is written to the program's input, which is then closed, so a program reading to EOF gets exactly that and does not hang.	`stdout` Stra `Str` `stderr` Stra `Str` `success` —a `Bool` `exit_code` Numa `Num`	Returns a `Record` with `stdout` (a `Str`), `stderr` (a `Str`), `success` (a `Bool`) and `exit_code` (a `Num`) — the same four fields `python_exec`/`js_exec`/`matlab_exec` already give back.

Examples

From the documentation, and run by the build -- the output and the figure below are what the engine actually produced. Simplest first.

r = exec("echo hello from a program", shell = true)
print("said: {trim(r.stdout)}")
print("success {r.success}, exit code {r.exit_code}")

failed = exec("exit 3", shell = true)
print("a failure is data, not an error: success {failed.success}, code {failed.exit_code}")

output

said: hello from a program
success true, exit code 0
a failure is data, not an error: success false, code 3

from file-io

How it works

module's own doc comment for why running a program and launching one are two builtins rather than one. Both are on check_sandbox's deny list, and the single guard at the top of this function is what applies it. Calling it again HERE would deny them always, sandboxed or not -- that guard is the only place self.sandboxed is read.

From the note above this builtin in the interpreter, where the reasoning was written down as it was built.