escapeshellcmd() escapes any characters in a string that might be used to trick a shell command into executing arbitrary commands. This function should be used to make sure that any data coming from user input is escaped before this data is passed to the exec() or system() functions, or to the backtick operator.
Following characters are preceded by a backslash:
are escaped only if they are not paired. In Windows, all these characters
% are replaced by a space instead.
$e = escapeshellcmd($userinput);
// here we don't care if $e has spaces
$f = escapeshellcmd($filename);
// and here we do, so we use quotes
system("touch \"/tmp/$f\"; ls -l \"/tmp/$f\"");