Method: Kernel#trace_var

Defined in:

eval.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:

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

  Yields:

  • (val)

  Returns:

  • (nil)

# File 'eval.c', line 2029

static VALUE
f_trace_var(int c, const VALUE *a, VALUE _)
{
    return rb_f_trace_var(c, a);
}