【BUUCTF】[GXYCTF2019]Ping Ping Ping1

It is obviously a problem of command injection

Try ls see

Note that spaces are filtered

Linux Space around

$IFS$9

  structure payload

?ip=127.0.0.1|cat$IFS$9`ls`

  Be careful `ls` Is executed as a command , There are also $()

You can see in the web page source code flag