discrepancy between path for binary and man page

Question

Systems often have multiple versions of binaries and the one selected depends on the priority in $PATH. For instance, the system I am using has a couple version of sort:

$ which sort
~/coreutils-8.25/bin/sort
$ ~/coreutils-8.25/bin/sort --version | head -n 1
sort (GNU coreutils) 8.25
$ /bin/sort --version | head -n 1
sort (GNU coreutils) 8.4

On the system I am using, the version from GNU coreutils 8.25 is selected by an invocation of sort because of its precedence in PATH. However, the MANPATH environment variable on the system has been established such that the man page for the sort from GNU coreutils 8.4 is displayed (i.e., for /bin/sort, which is not the binary having precedence).

A three-part question arises from this scenario.

First, is there a simple way to instruct man (or the shell) to use or produce a form of MANPATH that reflects PATH, or must one do this manually (i.e., by finding the paths to the man pages that are associated with each entry in PATH and then concatenating these man paths in the same order as PATH, an exercise that would have to be repeated any time a change is made to PATH)? Were there a mechanism to establish concordance between PATH and MANPATH, then the expected man page would be displayed automatically, avoiding the problem of inadvertently reading a man page for a version other than the one used by default.

Second, is there a command that allows one to quickly determine the path of the default man page (e.g., something akin to which "man sort", which would report the path of the man page that is displayed when executing man sort). For instance, when I type man sort, I have no indication of the specific file on the system that is being delivered to the pager.

Third, is there a way to obtain the man page for an explicit version of a command (something like man ~/coreutils-8.25/bin/sort in my case for the GNU coreutils 8.25 version of sort, rather than having to track down the associated file, which in my case can be found to be ~/coreutils-8.25/share/man/man1/sort.1 or ~/coreutils-8.25/man/sort.1).

Answer 1

For local installs such as that, I use a shell-script to setup the PATH, LD_LIBRARY_PATH and MANPATH values so that I get consistent results. Without a prop like that, you will not get automatic consistent results.

Here is an old example:

#!/bin/bash
# $Id: with-ncurses,v 1.1 2006/09/02 23:04:39 tom Exp $
export LIBS="-lncursesw"
for prefix in \
        /usr/local/ncurses6
do
        test  -f $prefix/lib/libncursesw.so && break
        test  -f $prefix/lib/libncursesw.a  && break
done

if [ -d $prefix/include/ncursesw ] ; then
        export CPPFLAGS="-I$prefix/include/ncursesw $CPPFLAGS"
        if [ $prefix != /usr ] ; then
                export CPPFLAGS="-I$prefix/include $CPPFLAGS"
        fi
fi

if [ $prefix != /usr ] ; then
        export PATH=`newpath -bd $prefix/bin`
        export LD_LIBRARY_PATH=`newpath -n LD_LIBRARY_PATH -bd $prefix/lib`
        export LIBS="-L$prefix/lib $LIBS"
        # this doesn't work for db30:
        # export LIBS="-static -L$prefix/lib $LIBS -shared"
fi

case `partition` in
rh*|md*)
        export MANPATH=$prefix/man:`manpath`
        ;;
*)
        export MANPATH=$prefix/man:`manpath -q`
        ;;
esac
eval $*

Making scripts like that portable is a problem, since there are no standards for the way MANPATH is used. But you can adapt things like that for specific systems.

The script, by the way, uses newpath to modify those variables and avoid duplicates.

Answer 2

2. You almost have it.  man -w sort shows you where it gets the man page for sort.

1 & 3. Probably not, since man pages can be anywhere.
3. You can do a brute-force search:

find / -name "sort.1*"

Answer 3

Add the following to your ~/.bashrc or ~/.profile:

export MANPATH="$HOME/coreutils-8.25/share/man:$(manpath)"

This will put your man page tree in $MANPATH first, before the default MANPATH (as supplied by the manpath command)

Answer 4

Assuming that you put your man pages next to your executables (i.e. executables in /somewhere/bin, man pages in /somewhere/man/manSECTION), and you're using a man implementation with a manpath command, such as most Linux systems and FreeBSD and OS X, just run manpath. It constructs a MANPATH variable that's parallel to your `PATH.

unset MANPATH
MANPATH=$(manpath)