perl, 101 bytes

Result

AC

Duration

1214ms

Code [DL]

$s=`dd`;
$s=~/T/;
$i=length$`;
$s=~s/(?<=\n.{$i}) /#/g;
$s=~s/(?<=K) *(?=#)/"#"x length$&/ge;
print$s

stdin

                          T                       
                                                  
                                                  
                                                  
                                                  
                                                  
                                                  
                                                  
                                                  
                                                  
                                                  
                                                  
                                                  
                                                  
                                                  
                                                  
                                                  
                                                  
                                                  
                                                  
                                                  
           K                                      

stdout

                          T                       
                          #                       
                          #                       
                          #                       
                          #                       
                          #                       
                          #                       
                          #                       
                          #                       
                          #                       
                          #                       
                          #                       
                          #                       
                          #                       
                          #                       
                          #                       
                          #                       
                          #                       
                          #                       
                          #                       
                          #                       
           K###############                       

stderr

2+1 records in
2+1 records out

strace

10    execve("/bin/sh", ["/bin/sh", "/root/script", "/volume/CODE"], 0x7ffcb03d0640 /* 7 vars */) = 0
12    execve("/usr/bin/perl", ["/usr/bin/perl", "/volume/CODE"], 0x5595bee9fd40 /* 7 vars */) = 0
11    execve("/bin/cat", ["cat", "-"], 0x5595bee9fd30 /* 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} ---
13    execve("/bin/dd", ["dd"], 0x5652c77855e0 /* 7 vars */) = 0
13    +++ exited with 0 +++
12    --- SIGCHLD {si_signo=SIGCHLD, si_code=CLD_EXITED, si_pid=13, 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 +++