rustup panics when piping to `grep -q`

[NickeZ]

I noticed that rustup panics in the case below.

 RUST_BACKTRACE=1 rustup show | grep -q ^nightly
thread 'main' panicked at 'failed printing to stdout: Broken pipe (os error 32)', libstd/io/stdio.rs:700:9
stack backtrace:
   0: std::sys::unix::backtrace::tracing::imp::unwind_backtrace
             at libstd/sys/unix/backtrace/tracing/gcc_s.rs:49
   1: std::panicking::default_hook::{{closure}}
             at libstd/sys_common/backtrace.rs:71
   2: std::panicking::rust_panic_with_hook
             at libstd/panicking.rs:227
             at libstd/panicking.rs:476
   3: std::panicking::continue_panic_fmt
             at libstd/panicking.rs:390
   4: std::panicking::begin_panic_fmt
             at libstd/panicking.rs:345
   5: std::io::stdio::_print
             at libstd/io/stdio.rs:700
             at libstd/io/stdio.rs:709
   6: rustup_init::rustup_mode::main
   7: rustup_init::run_rustup
   8: rustup_init::main
   9: std::rt::lang_start::{{closure}}
  10: main
  11: __libc_start_main
  12: <unknown>

[NickeZ]

I guess grep exits too fast for rustups liking?

       -q, --quiet, --silent
              Quiet; do not write anything to standard output.  Exit immediately with zero status if any match is found, even if an error was detected.  Also see the -s
              or --no-messages option.

[NickeZ]

Btw, I have two nightlies installed:

$ rustup show | grep ^nightly
7:nightly-2018-10-05-x86_64-unknown-linux-gnu
8:nightly-x86_64-unknown-linux-gnu

[NickeZ]

Even easier reproducer:

rustup show | head -1