Question

Shell command inside MySQL shell returns value:

mysql> \! echo 1
1

How to assign this result to MySQL variable? Like:

mysql> set @var = \! echo 1
1
    -> ;

ERROR 1064 (42000): You have an error in your SQL syntax; check the manual that corresponds to your MySQL server version for the right syntax to use near ” at line 1

Answer 1

The problem is that SET is a server command, which changes the state of variables held on the server; whereas system (and its \! shorthand) is a client command, which forks a process on the client. Whilst it could be possible for the client to transmit the forked process’s exit code to the server for storage in a user variable, I don’t think the MySQL command line client offers this functionality.

From mysql-5.5.29/client/mysql.cc:

3958: static int
3959: com_shell(String *buffer __attribute__((unused)),
3960:           char *line __attribute__((unused)))
3961: {
3962:   char *shell_cmd;
3963: 
3964:   /* Skip space from line begin */
3965:   while (my_isspace(charset_info, *line))
3966:     line++;
3967:   if (!(shell_cmd = strchr(line, ' ')))
3968:   {
3969:     put_info("Usage: \\! shell-command", INFO_ERROR);
3970:     return -1;
3971:   }
3972:   /*
3973:     The output of the shell command does not
3974:     get directed to the pager or the outfile
3975:   */
3976:   if (system(shell_cmd) == -1)
3977:   {
3978:     put_info(strerror(errno), INFO_ERROR, errno);
3979:     return -1;
3980:   }
3981:   return 0;
3982: }

Note in particular that the return value of the system(3) call is not stored anywhere; however the com_shell() function call will return -1 if the process exited with that code.