To see what Perl uses,

$ perl -le'use Config; print $Config{sh}'
/bin/sh
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But note that on many systems, /bin/sh is bash.

$ /bin/sh -c 'echo $SHELL'
/bin/bash
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If you want to use an alternate shell,

sub backticks_mysh {
  open(my $pipe, '-|', '/bin/mysh', '-c', $_[0])
     or return;
  local $/ = wantarray ? $/ : undef;
  <$pipe>
}
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