vim, 29 bytes

Result

WA

Duration

816ms

Code [DL]

:%s/.*\(.\)\(\1\| \).*/\1/
ZZ

Disassembly

:%s/.*\(.\)\(\1\| \).*/\1/<NL>ZZ

stdin

466 679
846 224
166 662
199 939
445 139
962 896
341 418
515 587
699 598
384 579
277 672
397 749
912 422
525 226
566 288
611 162
699 229
139 554
177 922
335 357
735 554
949 436
986 187
356 657
522 447
413 117
947 549
455 558
494 448
937 362
545 545
359 394

stdout

6
2
6
9
5
2
1
5
9
4
7
7
2
2
8
1
2
5
2
5
5
9
6
6
4
1
7
5
4
7
5
9

stderr

strace

10    execve("/bin/sh", ["/bin/sh", "/root/script", "/volume/CODE"], 0x7ffcc88dc490 /* 9 vars */) = 0
11    execve("/bin/cat", ["cat", "-"], 0x5639f6bded00 /* 9 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    execve("/usr/bin/vim", ["/usr/bin/vim", "-N", "-u", "NONE", "-i", "NONE", "-s", "/volume/CODE", "/tmp/out"], 0x5639f7aef288 /* 10 vars */) = 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} ---
13    execve("/bin/cat", ["cat", "/tmp/out"], 0x5639f6bdec98 /* 9 vars */) = 0
13    +++ exited with 0 +++
10    --- SIGCHLD {si_signo=SIGCHLD, si_code=CLD_EXITED, si_pid=13, si_uid=0, si_status=0, si_utime=0, si_stime=0} ---
14    execve("/bin/rm", ["rm", "/tmp/out"], 0x5639f6bdec98 /* 9 vars */) = 0
14    +++ exited with 0 +++
10    --- SIGCHLD {si_signo=SIGCHLD, si_code=CLD_EXITED, si_pid=14, si_uid=0, si_status=0, si_utime=0, si_stime=0} ---
10    +++ exited with 0 +++