sed - 从最后一行删除逗号

Question

如何从文件的最后一行删除逗号？
这是文件:

# cat ox_data_archive_r_20120727.json
{"name": "secondary_ua","type":"STRING"},
{"name": "request_ip","type":"STRING"},
{"name": "cb","type":"STRING"},

下面将删除所有3行中的逗号。

# sed 's/,$/\ /' ox_data_archive_r_20120727.json
{"name": "secondary_ua","type":"STRING"}
{"name": "request_ip","type":"STRING"}
{"name": "cb","type":"STRING"}

我只需要删除最后一个逗号。所以输出应该看起来像这样...

# cat newfile.json
{"name": "secondary_ua","type":"STRING"},
{"name": "request_ip","type":"STRING"},
{"name": "cb","type":"STRING"}

Answer 1

$ cat input.txt
{"name": "secondary_ua","type":"STRING"},
{"name": "request_ip","type":"STRING"},
{"name": "cb","type":"STRING"},
$ sed '$s/,$//' < input.txt
{"name": "secondary_ua","type":"STRING"},
{"name": "request_ip","type":"STRING"},
{"name": "cb","type":"STRING"}

从 GNU sed的文档中:

$: This address matches the last line of the last file of input, or the last line of each file when the -i or -s options are specified.