The s6-format-filter program
s6-format-filter processes lines according to its arguments, and
prints the result.
s6-format-filter format [ args... ]
- format is a format string that can contain the following special sequences:
%%, %s, and %0 to %9.
- For every line it reads on stdin, s6-format-filter prints format on
stdout, replacing %% with %, %0 with the command name
(probably s6-format-filter), %1 to %9 with the first
to the ninth argument in args, and %s with the input line.
- s6-format-filter exits 0 when it reads EOF.