exec() executes the given command, however it does not
output anything. It simply returns the last line from the
result of the command. If you need to execute a command and
have all the data from the command passed directly back
without any interference, use the
passthru() function.
If the array argument
is present, then the specified array will be filled with
every line of output from the command. Line endings, such as
\n, are not included in this array.
Note that if the array already contains some elements, exec() will append to the end of the
array. If you do not want the function to append elements,
call
unset() on the array before passing it to exec().
If the return_var
argument is present along with the
array argument, then the return status of the
executed command will be written to this variable.
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注: If you start a program using this function and want to leave it running in the background, you have to make sure that the output of that program is redirected to a file or some other output stream or else PHP will hang until the execution of the program ends.
See also system(),
passthru(), popen(),
escapeshellcmd(), and the backtick
operator.