$ 1 (ou $ 2, $ 3 ...) devem ser os argumentos dados a algum script.
Veja um exemplo de script:
#!/bin/bash
echo "\ is now $1"
echo "\ is now $2"
echo "\ is now $3"
E o exemplo de saída
jaba@lappy:/tmp$ ./example.sh
$1 is now
$2 is now
$3 is now
jaba@lappy:/tmp$ ./example.sh 1 2 3
$1 is now 1
$2 is now 2
$3 is now 3