One more, kinda unrelated, point. In Perl, unlike say in C#, the foreach loop variable is an alias to the list element and MAY be modified. So there is no reason to bother with the indices:

for (@cmd) {
  $_ = [split "\n", $_]->[0];
}
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Next thing ... you don't have to create an anonymous reference and then dereference it to get the first element from a list returned by a subroutine. A pair of braces is enough:

for (@cmd) {
  $_ = (split "\n", $_)[0];
}
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And last there really is no reason to avoid regexps. They tend to make the code simpler.

for (@cmd) {
  s/\n.*$//s;
}
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