How to execute a GDB command from a string variable?

Question

Say the debugged process has a string variable as follows:

char* cmd_str = "set confirm on";

How to execute the command from cmd_str in GDB?

(gdb) $cmd = cmd_str
(gdb) ???

Answer 1

You can use gdb's eval command, which runs printf on its arguments and then evaluates the result as a command.

(gdb) list
1   #include <stdlib.h>
2   main()
3   {
4       char *a = "set confirm off";
5   
6       pause();
7   }
(gdb) break 6
Breakpoint 1 at 0x400540: file cmdtest.c, line 6.
(gdb) run
Starting program: ./cmdtest 
Breakpoint 1, main () at cmd.c:6
6       pause();

(gdb) show confirm
Whether to confirm potentially dangerous operations is on.
(gdb) printf "%s", a
set confirm off(gdb) 
(gdb) eval "%s", a
(gdb) show confirm
Whether to confirm potentially dangerous operations is off.