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Re: system() and fork()/exec() within a UDF (in Unix) ?
Posted by: Roland Bouman
Date: June 25, 2008 01:35PM

Well, I just freshly compiled my udf, and installed it in MySQL 5.1.23:

mysql> create function sys_exec returns int soname 'lib_mysqludf_sys.so';
Query OK, 0 rows affected (0.74 sec)

I then set up test directory with a little file in it:

roland@roland-laptop:~/testudf$ pwd
/home/roland/testudf
roland@roland-laptop:~/testudf$ ls
test.txt

And then I ran this SQL:

mysql> set @status := sys_exec('cp /home/roland/testudf/test.txt /home/roland/testudf/copy_of_text.txt');
Query OK, 0 rows affected (0.01 sec)

mysql> select @status;
+---------+
| @status |
+---------+
| 0 |
+---------+
1 row in set (0.00 sec)

After that I checked the directory again:

roland@roland-laptop:~/testudf$ ls
copy_of_text.txt test.txt

And this indicates the file was copied, in accordance with the command passed to the system function.

So, lib_mysqludf_sys is working as I expect and intended.

Can you indicate how you determined that the program you want to call does not start? Are you sure the command you extract from the parameters is a valid command line? You can print it to the MySQL error log using:

fprintf(stderr, '%s', command_string);

To be sure, this is my UDF code:

my_bool sys_exec_init(
UDF_INIT *initid
, UDF_ARGS *args
, char *message
){
unsigned int i=0;
if(args->arg_count == 1
&& args->arg_type==STRING_RESULT){
return 0;
} else {
strcpy(
message
, "Expected exactly one string type parameter"
);
return 1;
}
}
void sys_exec_deinit(
UDF_INIT *initid
){
}
my_ulonglong sys_exec(
UDF_INIT *initid
, UDF_ARGS *args
, char *is_null
, char *error
){
return system(args->args[0]);
}


kind regards,

Roland Bouman
http://rpbouman.blogspot.com/

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