比如 man printf，说是没有入口，请高手帮忙。
pjq@localhost ~ $ man printf>printf
pjq@localhost ~ $ cat printf
PRINTF(1) User Commands PRINTF(1)
printf - format and print data
printf FORMAT [ARGUMENT]...
Print ARGUMENT(s) according to FORMAT, or execute according to OPTION:
--help display this help and exit
output version information and exit
FORMAT controls the output as in C printf. Interpreted sequences are:
" double quote
\NNN character with octal value NNN (1 to 3 digits)
\a alert (BEL)
\c produce no further output
\f form feed
\n new line
\r carriage return
\t horizontal tab
\v vertical tab
\xHH byte with hexadecimal value HH (1 to 2 digits)
\uHHHH Unicode (ISO/IEC 10646) character with hex value HHHH (4 digits)
Unicode character with hex value HHHHHHHH (8 digits)
%% a single %
%b ARGUMENT as a string with ‘\’ escapes interpreted, except that
octal escapes are of the form \0 or \0NNN
and all C format specifications ending with one of diouxXfeEgGcs, with
ARGUMENTs converted to proper type first. Variable widths are handled.
NOTE: your shell may have its own version of printf, which usually
supersedes the version described here. Please refer to your shell’s
documentation for details about the options it supports.
Written by David MacKenzie.
Report bugs to <firstname.lastname@example.org>.
Copyright © 2008 Free Software Foundation, Inc. License GPLv3+: GNU
GPL version 3 or later <http://gnu.org/licenses/gpl.html>
This is free software: you are free to change and redistribute it.
There is NO WARRANTY, to the extent permitted by law.
The full documentation for printf is maintained as a Texinfo manual.
If the info and printf programs are properly installed at your site,
should give you access to the complete manual.
GNU coreutils 18.104.22.168-f088d-dirtJanuary 2008 PRINTF(1)