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with cmd it only works, because with the MuonTrap it doesn't? <div class="snippet-

No Works with Nerves about muontrap HOT 3 CLOSED

fhunleth commented on June 24, 2024

No Works with Nerves

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Comments (3)

joserpintuitivo commented on June 24, 2024

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

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

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joserpintuitivo commented on June 24, 2024

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

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fhunleth commented on June 24, 2024

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}

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