Method: Kernel#trace_var

Defined in:

variable.c

#trace_var(symbol, cmd) ⇒ nil #trace_var(symbol) {|val| ... } ⇒ nil

Controls tracing of assignments to global variables. The parameter symbol identifies the variable (as either a string name or a symbol identifier). cmd (which may be a string or a Proc object) or block is executed whenever the variable is assigned. The block or Proc object receives the variable’s new value as a parameter. Also see Kernel::untrace_var.

trace_var :$_, proc {|v| puts "$_ is now '#{v}'" }
$_ = "hello"
$_ = ' there'

produces:

$_ is now 'hello'
$_ is now ' there'

Overloads:

• #trace_var(symbol, cmd) ⇒ nil

  Returns:
• #trace_var(symbol) {|val| ... } ⇒ nil

  Yields:

  • (val)

  Returns:

# File 'variable.c', line 653

VALUE
rb_f_trace_var(int argc, const VALUE *argv)
{
    VALUE var, cmd;
    struct global_entry *entry;
    struct trace_var *trace;

    if (rb_scan_args(argc, argv, "11", &var, &cmd) == 1) {
  cmd = rb_block_proc();
    }
    if (NIL_P(cmd)) {
  return rb_f_untrace_var(argc, argv);
    }
    entry = rb_global_entry(rb_to_id(var));
    if (OBJ_TAINTED(cmd)) {
  rb_raise(rb_eSecurityError, "Insecure: tainted variable trace");
    }
    trace = ALLOC(struct trace_var);
    trace->next = entry->var->trace;
    trace->func = rb_trace_eval;
    trace->data = cmd;
    trace->removed = 0;
    entry->var->trace = trace;

    return Qnil;
}