z80, 57 bytes

Result

AC

Duration

837ms

Code [DL]

00000000  16 01 1e 01 cd 03 80 47  78 fe 54 20 02 16 00 78  |.......Gx.T ...x|
00000010  fe 4b 20 02 1e 00 7a fe  00 28 08 7b fe 00 28 03  |.K ...z..(.{..(.|
00000020  78 18 04 3e 58 18 00 cd  00 80 7a b3 20 01 76 14  |x..>X.....z. .v.|
00000030  7a fe 33 20 02 16 00 18  cb                       |z.3 .....|
00000039

Disassembly

        ORG     0000h

        LD      D,01h
        LD      E,01h
L0004:  CALL    8003h
        LD      B,A
        LD      A,B
        CP      54h             ; 'T'
        JR      NZ,L000F
        LD      D,00h
L000F:  LD      A,B
        CP      4Bh             ; 'K'
        JR      NZ,L0016
        LD      E,00h
L0016:  LD      A,D
        CP      00h
        JR      Z,L0023
        LD      A,E
        CP      00h
        JR      Z,L0023
        LD      A,B
        JR      L0027

L0023:  LD      A,58h           ; 'X'
        JR      L0027

L0027:  CALL    8000h
        LD      A,D
        OR      E
        JR      NZ,L002F
        HALT
L002F:  INC     D
        LD      A,D
        CP      33h             ; '3'
        JR      NZ,L0037
        LD      D,00h
L0037:  JR      L0004

stdin

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       K                                          

stdout

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       XXXX

stderr

strace

10    execve("/bin/sh", ["/bin/sh", "/root/script", "/volume/CODE"], 0x7ffde2c06ce0 /* 7 vars */) = 0
11    execve("/bin/cat", ["cat", "-"], 0x56011338dd38 /* 7 vars */) = 0
12    execve("/usr/bin/z80golf", ["/usr/bin/z80golf", "/volume/CODE"], 0x56011338dd50 /* 7 vars */) = 0
11    +++ exited with 0 +++
10    --- SIGCHLD {si_signo=SIGCHLD, si_code=CLD_EXITED, si_pid=11, si_uid=0, si_status=0, si_utime=0, si_stime=0} ---
12    +++ exited with 0 +++
10    --- SIGCHLD {si_signo=SIGCHLD, si_code=CLD_EXITED, si_pid=12, si_uid=0, si_status=0, si_utime=0, si_stime=0} ---
10    +++ exited with 0 +++