perl, 91 bytes

Result

AC

Duration

643ms

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                      
                           #                      
                           #                      
                           #                      
                           #                      
                           #                      
                           #                      
                           #                      
                           #                      
                           #                      
                           #                      
                           #                      
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                           #                      
                           #                      
     K######################                      

stderr

3+1 records in
3+1 records out

strace

10    execve("/bin/sh", ["/bin/sh", "/root/script", "/volume/CODE"], 0x7ffc02543b20 /* 7 vars */) = 0
11    execve("/bin/cat", ["cat", "-"], 0x55fc158bad30 /* 7 vars */ <unfinished ...>
12    execve("/usr/bin/perl", ["/usr/bin/perl", "/volume/CODE"], 0x55fc158bad40 /* 7 vars */ <unfinished ...>
11    <... execve resumed> )            = 0
12    <... execve resumed> )            = 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"], 0x5562423095e0 /* 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 +++