$ fq -ni
null> 123 | var("a")
null> "bb" | var("bb")
null> var
{
  "a": 123,
  "bb": "bb"
}
null> $a
123
null> "aa" | var("a")
null> var
{
  "a": "aa",
  "bb": "bb"
}
null> $a
"aa"
null> var("a"; empty)
null> $a
error: repl:1:0: variable not defined: $a
null> var
{
  "bb": "bb"
}
null> . | repl
> null> $bb
"bb"
> null> ^D
null> var("bb"; empty)
null> var
{}
null> 123 | var("a b")
error: invalid variable name: a b
null> 123 | var(null)
error: invalid variable name: null
null> ^D
$ fq -d mp3 -i . /test.mp3
mp3> .frames[0] | var("f")
mp3> $f
    |00 01 02 03 04 05 06 07 08 09 0a 0b 0c 0d 0e 0f|0123456789abcdef|.frames[0]{}: (mp3_frame)
0x20|                                       ff fb 40|             ..@|  header{}:
0x30|c0                                             |.               |
0x30|   00 00 00 00 00 00 00 00 00 00 00 00 00 00 00| ...............|  side_info{}:
0x40|00 00                                          |..              |
0x40|      49 6e 66 6f 00 00 00 0f 00 00 00 02 00 00|  Info..........|  xing{}: (xing)
0x50|02 57 00 a6 a6 a6 a6 a6 a6 a6 a6 a6 a6 a6 a6 a6|.W..............|
*   |until 0xdd.7 (156)                             |                |
0xd0|                                          00 00|              ..|  padding: raw bits
0xe0|00 00 00                                       |...             |
    |                                               |                |  crc_calculated: "827a" (raw bits)
mp3> ^D