Method: Kernel#system

Defined in:

process.c

#system([env, ], options = {}, exception: false) ⇒ true, ... #system([env, ], *args, options = {}, exception: false) ⇒ true, ...

Creates a new child process by doing one of the following in that process:

• Passing string command_line to the shell.

• Invoking the executable at exe_path.

This method has potential security vulnerabilities if called with untrusted input; see Command Injection.

Returns:

• true if the command exits with status zero.

• false if the exit status is a non-zero integer.

• nil if the command could not execute.

Raises an exception (instead of returning false or nil) if keyword argument exception is set to true.

Assigns the command’s error status to $?.

The new process is created using the system system call; it may inherit some of its environment from the calling program (possibly including open file descriptors).

Argument env, if given, is a hash that affects ENV for the new process; see Execution Environment.

Argument options is a hash of options for the new process; see Execution Options.

The first required argument is one of the following:

• command_line if it is a string, and if it begins with a shell reserved word or special built-in, or if it contains one or more meta characters.

• exe_path otherwise.

Argument command_line

String argument command_line is a command line to be passed to a shell; it must begin with a shell reserved word, begin with a special built-in, or contain meta characters:

system('if true; then echo "Foo"; fi')          # => true  # Shell reserved word.
system('exit')                                  # => true  # Built-in.
system('date > /tmp/date.tmp')                  # => true  # Contains meta character.
system('date > /nop/date.tmp')                  # => false
system('date > /nop/date.tmp', exception: true) # Raises RuntimeError.

Assigns the command’s error status to $?:

system('exit')                             # => true  # Built-in.
$?                                         # => #<Process::Status: pid 640610 exit 0>
system('date > /nop/date.tmp')             # => false
$?                                         # => #<Process::Status: pid 640742 exit 2>

The command line may also contain arguments and options for the command:

system('echo "Foo"') # => true

Output:

Foo

See Execution Shell for details about the shell.

Raises an exception if the new process could not execute.

Argument exe_path

Argument exe_path is one of the following:

• The string path to an executable to be called.

• A 2-element array containing the path to an executable and the string to be used as the name of the executing process.

Example:

system('/usr/bin/date') # => true # Path to date on Unix-style system.
system('foo')           # => nil  # Command failed.

Output:

Mon Aug 28 11:43:10 AM CDT 2023

Assigns the command’s error status to $?:

system('/usr/bin/date') # => true
$?                      # => #<Process::Status: pid 645605 exit 0>
system('foo')           # => nil
$?                      # => #<Process::Status: pid 645608 exit 127>

Ruby invokes the executable directly. This form does not use the shell; see Arguments args for caveats.

system('doesnt_exist') # => nil

If one or more args is given, each is an argument or option to be passed to the executable:

system('echo', 'C*')             # => true
system('echo', 'hello', 'world') # => true

Output:

C*
hello world

Raises an exception if the new process could not execute.

Overloads:

• #system([env, ], options = {}, exception: false) ⇒ true, ...

  Returns:

  • (true, false, nil)
• #system([env, ], *args, options = {}, exception: false) ⇒ true, ...

  Returns:

  • (true, false, nil)

# File 'process.c', line 4845

static VALUE
rb_f_system(int argc, VALUE *argv, VALUE _)
{
    rb_thread_t *th = GET_THREAD();
    VALUE execarg_obj = rb_execarg_new(argc, argv, TRUE, TRUE);
    struct rb_execarg *eargp = rb_execarg_get(execarg_obj);

    struct rb_process_status status = {0};
    eargp->status = &status;

    last_status_clear(th);

    // This function can set the thread's last status.
    // May be different from waitpid_state.pid on exec failure.
    rb_pid_t pid = rb_execarg_spawn(execarg_obj, 0, 0);

    if (pid > 0) {
        VALUE status = rb_process_status_wait(pid, 0);
        struct rb_process_status *data = rb_check_typeddata(status, &rb_process_status_type);
        // Set the last status:
        rb_obj_freeze(status);
        th->last_status = status;

        if (data->status == EXIT_SUCCESS) {
            return Qtrue;
        }

        if (data->error != 0) {
            if (eargp->exception) {
                VALUE command = eargp->invoke.sh.shell_script;
                RB_GC_GUARD(execarg_obj);
                rb_syserr_fail_str(data->error, command);
            }
            else {
                return Qnil;
            }
        }
        else if (eargp->exception) {
            VALUE command = eargp->invoke.sh.shell_script;
            VALUE str = rb_str_new_cstr("Command failed with");
            rb_str_cat_cstr(pst_message_status(str, data->status), ": ");
            rb_str_append(str, command);
            RB_GC_GUARD(execarg_obj);
            rb_exc_raise(rb_exc_new_str(rb_eRuntimeError, str));
        }
        else {
            return Qfalse;
        }

        RB_GC_GUARD(status);
    }

    if (eargp->exception) {
        VALUE command = eargp->invoke.sh.shell_script;
        RB_GC_GUARD(execarg_obj);
        rb_syserr_fail_str(errno, command);
    }
    else {
        return Qnil;
    }
}