vim, 29 bytes

Result

AC

Duration

1144ms

Code [DL]

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

Disassembly

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

stdin

461 647
947 453
631 314
357 449
349 246
144 449
328 483
522 265
841 761
887 881
918 843
895 594
733 752
839 392
637 176
211 331
688 689
945 346
491 113
351 154
673 751
255 553
238 422
299 696
199 339
135 553
945 543
815 993
149 973
966 624
799 239
936 334

stdout

1
7
1
4
9
4
8
2
1
8
8
5
3
9
7
3
8
5
1
1
3
5
2
9
3
5
5
9
9
6
9
3

stderr

strace

10    execve("/bin/sh", ["/bin/sh", "/root/script", "/volume/CODE"], 0x7ffc79431e30 /* 9 vars */) = 0
11    execve("/bin/cat", ["cat", "-"], 0x5605ca917d00 /* 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"], 0x5605caf48288 /* 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=1} ---
13    execve("/bin/cat", ["cat", "/tmp/out"], 0x5605ca917c98 /* 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"], 0x5605ca917c98 /* 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 +++