sed: Exit status
2.3 Exit status
===============
An exit status of zero indicates success, and a nonzero value indicates
failure. GNU 'sed' returns the following exit status error values:
0
Successful completion.
1
Invalid command, invalid syntax, invalid regular expression or a
GNU 'sed' extension command used with '--posix'.
2
One or more of the input file specified on the command line could
not be opened (e.g. if a file is not found, or read permission is
denied). Processing continued with other files.
4
An I/O error, or a serious processing error during runtime, GNU
'sed' aborted immediately.
Additionally, the commands 'q' and 'Q' can be used to terminate 'sed'
with a custom exit code value (this is a GNU 'sed' extension):
$ echo | sed 'Q42' ; echo $?
42