writable?

/*
 * call-seq:
 *    File.writable?(file_name)   => true or false
 *
 * Returns <code>true</code> if the named file is writable by the effective
 * user id of this process.
 */

static VALUE
test_w(obj, fname)
    VALUE obj, fname;
{
    SafeStringValue(fname);
    if (eaccess(StringValueCStr(fname), W_OK) < 0) return Qfalse;
    return Qtrue;
}