Apagar o último caracter

[andrelucio . fc]

Opa, pessoal.

Estou precisando apagar a última virgula da última linha. Por exemplo:

Antes:

{"MAC":"18:81:0e:23:13:b5", "IP":"172.16.220.26", "First Act":"1553634049", "Last Act":"1553634236", "Total Act":"187"},$

{"MAC":"d4:63:c6:a5:1e:6b", "IP":"172.16.221.221", "First Act":"1553634287", "Last Act":"1553634295", "Total Act":"8"},$

{"MAC":"cc:c3:ea:b4:7b:76", "IP":"172.16.221.36", "First Act":"1553626192", "Last Act":"1553634238", "Total Act":"8046"},$

$

Depois:

{"MAC":"18:81:0e:23:13:b5", "IP":"172.16.220.26", "First Act":"1553634049", "Last Act":"1553634236", "Total Act":"187"},$

{"MAC":"d4:63:c6:a5:1e:6b", "IP":"172.16.221.221", "First Act":"1553634287", "Last Act":"1553634295", "Total Act":"8"},$

{"MAC":"cc:c3:ea:b4:7b:76", "IP":"172.16.221.36", "First Act":"1553626192", "Last Act":"1553634238", "Total Act":"8046"}$

$

Obs: Existe uma linha em branco na última linha de fato.