Call details for Shell commands in Perl

In PERL development, system commands can usually be executed using the systems function or the ' operator ', but pay attention to alias, BG, bind, break, Builtin, CD, command, Compgen, complete, continue, Declare, dirs, Disown, Echo, enable, Eval, exec, exit, export, FC, FG, Getopts, hash, help, history, jobs, kill, le T, local, logout, popd, printf, pushd, pwd, read, ReadOnly, return, set, shift, shopt, source, suspend, test, times, tra P, type, typeset, Ulimit, Umask, Unalias, unset, wait, etc. shell internal commands (that is, a command that does not execute files in the file system) can be executed directly, and the error is that the file or directory cannot be found. You can add sh–c to the command before you implement it.   And for CD, Umask and other session-type commands, should use the internal functions of Perl chdir, umask, etc. to achieve more reliable functions. Complement: If the system calls the background program, it is certainly hope that does not affect the foreground of the CGI program to respond to HTTP requests, this time, notice that Firefox can immediately get system calls after the output, ie not, Will wait until the daemon that is called by the system finishes executing before it gets the HTTP output. In fact, only need in the system called the background program Riga >/dev/null 2>&1 output redirection can solve the problem of IE response.