ruby, 53 bytes

Result

AC

Duration

857ms

Code [DL]

puts $<.chars.map{|c|c>'@'&&c<'['?'1':'0'}.join.chop!

stdin

AbcDEfgHiJKlmNopQRStuVwXyZ

stdout

10011001011001001110010101

stderr

/volume/CODE:1: warning: ARGF#chars is deprecated; use #each_char instead

strace

13    execve("/bin/sh", ["/bin/sh", "/root/script", "/volume/CODE"], 0x7fffc7ea92d0 /* 9 vars */) = 0
14    execve("/bin/cat", ["cat", "-"], 0x55f83e2f6d40 /* 9 vars */) = 0
15    execve("/usr/local/ruby-2.7.1/bin/ruby", ["/usr/local/ruby-2.7.1/bin/ruby", "/volume/CODE"], 0x55f83e2f6d60 /* 9 vars */) = 0
14    +++ exited with 0 +++
13    --- SIGCHLD {si_signo=SIGCHLD, si_code=CLD_EXITED, si_pid=14, si_uid=0, si_status=0, si_utime=0, si_stime=0} ---
15    +++ exited with 0 +++
13    --- SIGCHLD {si_signo=SIGCHLD, si_code=CLD_EXITED, si_pid=15, si_uid=0, si_status=0, si_utime=6, si_stime=2} ---
13    +++ exited with 0 +++