This function is identical to the backtick operator.
On Windows, the underlying pipe is opened in text mode which can cause the function to fail for binary output. Consider to use popen instead for such cases.
The command that will be executed.
A string containing the output from the executed command, false if the pipe cannot be established or null if an error occurs or the command produces no output.
This function can return null both when an error occurs or the program produces no output. It is not possible to detect execution failures using this function. exec should be used when access to the program exit code is required.
Exceptions and Errors
An E_WARNING level error is generated when the pipe cannot be established.