End of Life Ruby 3.2 has reached end of life and gets no more fixes. Switch to Ruby 4.0 →

instance method

Kernel#trace_var

trace_var(symbol, cmd ) → nil

trace_var(symbol) {|val| block } → nil

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

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.

Example

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

produces:

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

See also #throw #trap #then #untrace_var also in 4.1 · 4.0 · 3.4 · 3.3 · 3.1 · 3.0

‹ prev#throw next ›#trap