No Works with Nerves

[joserpintuitivo]

iex(3)> MuonTrap.cmd("echo", ["hello"])
** (ErlangError) Erlang error: :enoent
    (muontrap 1.0.0) lib/muontrap/options.ex:52: MuonTrap.Options.validate("echo", ["hello"], [])
    (muontrap 1.0.0) lib/muontrap.ex:99: MuonTrap.cmd/3
    iex:3: (file)

[joserpintuitivo]

with cmd it only works, because with the MuonTrap it doesn't?

iex(3)> cmd("echo hello")
hello
0

[joserpintuitivo]

iex(1)> System.cmd("echo", ["hello"])
** (ErlangError) Erlang error: :enoent
    (elixir 1.12.3) lib/system.ex:1041: System.cmd("echo", ["hello"], [])

[fhunleth]

Nerves has a very limited set of Linux utilities available. You found an interesting case where echo is not available. However, it's possible to still use echo as a built-in shell command.

To see what's available, run ls on /bin and /usr/bin. Here's what I get:

iex(1)> ls "/bin"
ash         busybox     cat         cp          date        dd          df
dmesg       grep        kill        ls          mkdir       mknod       mktemp
mount       mv          pidof       ping        ping6       ps          pwd
rm          rmdir       sed         sh          sleep       touch       umount

The cmd/1 function runs whatever you pass it in a shell via sh -c. You can do the same thing with System.cmd/3 and MuonTrap.cmd/3:

iex(4)> System.cmd("echo", ["hello"])
** (ErlangError) Erlang error: :enoent
    (elixir 1.14.1) lib/system.ex:1060: System.cmd("echo", ["hello"], [])
    iex:4: (file)
iex(4)> System.cmd("sh", ["-c", "echo hello"])
{"hello\n", 0}