vfork() is an obsolete optimization. Before good memory management, fork() made a full copy of the parent’s memory, so it was pretty expensive. since in many cases a fork() was followed by exec(), which discards the current memory map and creates a new one, it was a needless expense. Nowadays, fork() doesn’t copy the memory; … Read more
A -exec command must be terminated with a ; (so you usually need to type \; or ‘;’ to avoid interpretion by the shell) or a +. The difference is that with ;, the command is called once per file, with +, it is called just as few times as possible (usually once, but there … Read more
The exec built-in command mirrors functions in the kernel, there are a family of them based on execve, which is usually called from C. exec replaces the current program in the current process, without forking a new process. It is not something you would use in every script you write, but it comes in handy … Read more
They have slightly different purposes. exec() is for calling a system command, and perhaps dealing with the output yourself. system() is for executing a system command and immediately displaying the output – presumably text. passthru() is for executing a system command which you wish the raw return from – presumably something binary. Regardless, I suggest … Read more
shell_exec returns all of the output stream as a string. exec returns the last line of the output by default, but can provide all output as an array specifed as the second parameter. See http://php.net/manual/en/function.shell-exec.php http://php.net/manual/en/function.exec.php
system The system method calls a system program. You have to provide the command as a string argument to this method. For example: >> system(“date”) Wed Sep 4 22:03:44 CEST 2013 => true The invoked program will use the current STDIN, STDOUT and STDERR objects of your Ruby program. In fact, the actual return value … Read more
For statements, use exec(string) (Python 2/3) or exec string (Python 2): >>> mycode=”print “hello world”” >>> exec(mycode) Hello world When you need the value of an expression, use eval(string): >>> x = eval(“2+2”) >>> x 4 However, the first step should be to ask yourself if you really need to. Executing code should generally be … Read more
The short answer, or TL;DR Basically, eval is used to evaluate a single dynamically generated Python expression, and exec is used to execute dynamically generated Python code only for its side effects. eval and exec have these two differences: eval accepts only a single expression, exec can take a code block that has Python statements: … Read more