lua os.execute() return wrong value

Question

have a problem:

 local stat = assert(os.execute("/usr/bin/pgrep -f 'tail -F /opt/aaa' >& /dev/null"))
 print(stat)  --> 0

But when I type pgrep -f 'tail -F /opt/aaa' >& /dev/null in bash, and then call echo $? it returns 1. Has anybody encountered this before, or know the reason why ;-) what happened?

In Lua 5.2 you get the status. See http://www.lua.org/manual/5.2/manual.html#pdf-os.execute — lhf, Oct 26 '13 at 13:09
@lhf I had try this under 5.2.2, but it does't return the correct value too. It returns `true` and `exit` — ms2008, Oct 26 '13 at 14:55

score 3 · Answer 1 · answered Oct 26 '13 at 13:09

3

Doesn't seem to be a Lua problem to me, os.execute is just wrapping a call to system:

 static int os_execute (lua_State *L) {
    lua_pushinteger(L, system(luaL_optstring(L, 1, NULL)));
    return 1;
 }

If you try the C alternative you have the correct result code?

 #include <stdio.h>
 #include <string.h>

 int main ()
 {
    char command[100];
    int result;

    strcpy( command, "/usr/bin/pgrep -f 'tail -F /opt/aaa' >& /dev/null" );
    result = system(command);

    return(0);
  }

answered Oct 26 '13 at 13:09

guilespi

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I gave it a try, but unfortunately it return 0 too. – ms2008 Oct 26 '13 at 14:05
Maybe http://stackoverflow.com/questions/10931134/return-value-of-system-function-call-in-c-used-to-run-a-python-program?rq=1 this related python question answers _in part_ your question – guilespi Oct 26 '13 at 14:14

lua os.execute() return wrong value

1 Answers1