msys2环境下为帮助手册Manual建立索引

msys2部署以后，有会有一些文件目录是原生Linux所没有的，比如“根目录”下的mingw32和mingw64路径：

在部署iverilog的时候，发现包名称是带有mingw32/w64的：

这样的结果是，iverilog编译器和vvp仿真工具都安装在了msys64/mingw32/bin目录下（mingw64和ucrt64类似，放在msys64/mingw64/bin和msys64/ucrt64/bin），而对应的帮助手册（man，System Reference Manual）放在了msys64/mingw32/share/man下，

此时进行手册查询：

man iverilog

会提示找不到手册项：

No manual entry for iverilog

要解决这个问题，需要搞定mandb命令，即Manual Index Database，与之相关的还有manpath命令。

给出mandb(8)的手册内容：

MANDB(8) Manual pager utils MANDB(8)

NAME
mandb - create or update the manual page index caches

SYNOPSIS
mandb [-dqsucpt?V] [-C file] [manpath]
mandb [-dqsut] [-C file] -f filename ...

DESCRIPTION
mandb is used to initialise or manually update index database caches. The caches contain information relevant to the current state of the manual page system and the information
stored within them is used by the man-db utilities to enhance their speed and functionality.

When creating or updating an index, mandb will warn of bad ROFF .so requests, bogus manual page filenames and manual pages from which the whatis cannot be parsed.

Supplying mandb with an optional colon-delimited path will override the internal system manual page hierarchy search path, determined from information found within the man-db
configuration file.

DATABASE CACHES
mandb can be compiled with support for any one of the following database types.

Name Async Filename
──────────────────────────────────────
Berkeley db Yes index.bt
GNU gdbm Yes index.db
UNIX ndbm No index.(dir|pag)

Those database types that support asynchronous updates provide enhanced speed at the cost of possible corruption in the event of unusual termination. In an unusual case where
this has occurred, it may be necessary to rerun mandb with the -c option to re-create the databases from scratch.

OPTIONS
-d, --debug
Print debugging information.

-q, --quiet
Produce no warnings.

-s, --no-straycats
Do not spend time looking for or adding information to the databases regarding stray cats.

-p, --no-purge
Do not spend time checking for deleted manual pages and purging them from the databases.

-c, --create
By default, mandb will try to update any previously created databases. If a database does not exist, it will create it. This option forces mandb to delete previous data‐
bases and re-create them from scratch, and implies --no-purge. This may be necessary if a database becomes corrupt or if a new database storage scheme is introduced in
the future.

-u, --user-db
Create user databases only, even with write permissions necessary to create system databases.

-t, --test
Perform correctness checks on manual pages in the hierarchy search path. With this option, mandb will not alter existing databases.

-f, --filename
Update only the entries for the given filename. This option is not for general use; it is used internally by man when it has been compiled with the MAN_DB_UPDATES option
and finds that a page is out of date. It implies -p and disables -c and -s.

-C file, --config-file=file
Use this user configuration file rather than the default of ~/.manpath.

-?, --help
Show the usage message, then exit.

--usage
Print a short usage message and exit.

-V, --version
Show the version, then exit.

EXIT STATUS
0 Successful program execution.

1 Usage, syntax, or configuration file error.

2 Operational error.

3 A child process failed.

DIAGNOSTICS
The following warning messages can be emitted during database building.

<filename>: whatis parse for page(sec) failed
An attempt to extract whatis line(s) from the given <filename> failed. This is usually due to a poorly written manual page, but if many such messages are emitted it is
likely that the system contains non-standard manual pages which are incompatible with the man-db whatis parser. See the WHATIS PARSING section in lexgrog(1) for more in‐
formation.

<filename>: is a dangling symlink
<filename> does not exist but is referenced by a symbolic link. Further diagnostics are usually emitted to identify the <filename> of the offending link.

<filename>: bad symlink or ROFF `.so' request
<filename> is either a symbolic link to, or contains a ROFF include request to, a non existent file.

<filename>: ignoring bogus filename
The <filename> may or may not be a valid manual page but its name is invalid. This is usually due to a manual page with sectional extension <x> being put in manual page
section <y>.

<filename_mask>: competing extensions
The wildcard <filename_mask> is not unique. This is usually caused by the existence of both a compressed and uncompressed version of the same manual page. All but the
most recent are ignored.

FILES
/etc/man_db.conf
man-db configuration file.

/var/cache/man/index.(bt|db|dir|pag)
An FHS compliant global index database cache.

Older locations for the database cache included:

/usr/man/index.(bt|db|dir|pag)
A traditional global index database cache.

/var/catman/index.(bt|db|dir|pag)
An alternate or FSSTND compliant global index database cache.

SEE ALSO
lexgrog(1), man(1), manpath(5), catman(8)

The WHATIS PARSING section formerly in this manual page is now part of lexgrog(1).

AUTHOR
Wilf. (G.Wilford@ee.surrey.ac.uk).
Fabrizio Polacco (fpolacco@debian.org).
Colin Watson (cjwatson@debian.org).

BUGS
https://savannah.nongnu.org/bugs/?group=man-db

2.9.4 2021-02-08 MANDB(8)

manpath命令对man索引建立的说明是：

MANPATH(1) Manual pager utils MANPATH(1)

NAME
manpath - determine search path for manual pages

SYNOPSIS
manpath [-qgdc?V] [-m system[,...]] [-C file]

DESCRIPTION
If $MANPATH is set, manpath will simply display its contents and issue a warning. If not, manpath will determine a suitable manual page hierarchy search path and display the re‐
sults.

The colon-delimited path is determined using information gained from the man-db configuration file – (/etc/man_db.conf) and the user's environment.

OPTIONS
-q, --quiet
Do not issue warnings.

-d, --debug
Print debugging information.

-c, --catpath
Produce a catpath as opposed to a manpath. Once the manpath is determined, each path element is converted to its relative catpath.

-g, --global
Produce a manpath consisting of all paths named as "global" within the man-db configuration file.

-m system[,...], --systems=system[,...]
If this system has access to other operating system's manual hierarchies, this option can be used to include them in the output of manpath. To include NewOS's manual page
hierarchies use the option -m NewOS.

The system specified can be a combination of comma delimited operating system names. To include the native operating system's manual page hierarchies, the system name man
must be included in the argument string. This option will override the $SYSTEM environment variable.

-C file, --config-file=file
Use this user configuration file rather than the default of ~/.manpath.

-?, --help
Print a help message and exit.

--usage
Print a short usage message and exit.

-V, --version
Display version information.

ENVIRONMENT
MANPATH
If $MANPATH is set, manpath displays its value rather than determining it on the fly. If $MANPATH is prefixed by a colon, then the value of the variable is appended to
the list determined from the content of the configuration files. If the colon comes at the end of the value in the variable, then the determined list is appended to the
content of the variable. If the value of the variable contains a double colon (::), then the determined list is inserted in the middle of the value, between the two
colons.

SYSTEM If $SYSTEM is set, it will have the same effect as if it had been specified as the argument to the -m option.

FILES
/etc/man_db.conf man-db configuration file.

msys2环境下为帮助手册Manual建立索引

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