On Line Man Pages from Terminal

Question

With the risk of raising a question that might already have an answer, i would like to ask if anybody knows if and how is it possible to read man pages in my terminal for programs/apps that are not installed in my system using online sources/online tools.

I made a stackexchange and google search but found nothing about this issue.

For example man grep will raise the grep manual as expected. On the other hand man agrep will give an error since agrep is not installed. In order to read agrep manual i have to google agrep man pages , getting results like this : https://linux.die.net/man/1/agrep

PS: BTW it seems strange to me that http://man7.org/linux/man-pages/dir_all_alphabetic.html do not provide agrep...

I wonder if it is possible to run man agrep or similar command from my terminal (without installing agrep) and read agrep man pages in terminal as usual man works.

I don't expect all man pages of the world to be locally available; i just wonder if there is any tricky way to use man (or even other command) to search and display man pages of not installed progs without having to open browser, type keyword, search in results etc.

PS: As noticed by Kusalananda, raising web queries may lead to results not suitable for particular distro version (different versions result will pop up). So the best (in my dream) would be if there was a kind of Distro specific (Debian in my case) internal / built in command (or even a switch) that could retrieve online man pages specifically for my setup (i.e something like : man --online agrep or onlineman agrep). It seems not.

Answer 1

You can use links : links -dump https://linux.die.net/man/1/agrep | less . Just change the category and name and you're good.

Answer 2

If this were Ubuntu, you could use the dman command from the bikeshed package. From man dman:

dman   is   a   script   that   remotely   retrieves   manpages    from
http://manpages.ubuntu.com, but reads them on the local system.

This  is  often  useful  to read a manpage of a utility that you do not
have installed on the local system.

It will cycle through each manpage section available for a given TOPIC.

IIRC, dman is a script, so it might be possible to modify it to work with https://manpages.debian.org.

Answer 3

As an alternative, you might consider the lynx text browser instead. That way, you need only enter:

lynx https://linux.die.net/man/1/agrep

It's worked for me in many situations, and appears to be widely available in software repositories for many systems.

As far as knowing you got the version for your system, I don't think there's any way to do that without getting the version number from the one you have installed, and looking in the man page you're trying to read.

Answer 4

Using online services to display manuals is cool, but as soon as i read @Kusalananda comment about pulling man pages out of installation packages, i got somehow obsessed to implement this technique that will ensure that i will read the correct manual for my distro.

The only bug in bellow solution is that it is based on recent versions of apt/dpkg that are available in Debian Testing 8.6 and might not be available in other systems.

Extract the man pages from .deb files without download
Locate the deb file like if you had plans to install the package in question (i.e yade):

apt-get --print-uris download yade
'http://httpredir.debian.org/debian/pool/main/y/yade/yade_2016.06a-7_amd64.deb' yade_2016.06a-7_amd64.deb 1621148 SHA256:26c0d84484a92ae9c2828edaa63243eb764378d79191149970926aa3ec40cdd4

PS: --print-uris switch prints the url of deb package but deb is not downloaded.

Find the man pages hidden in this deb file:

dpkg -c <(curl -sL -o- http://httpredir.debian.org/debian/pool/main/y/yade/yade_2016.06a-7_amd64.deb) |grep "man/man" |grep -vE "\/$" |awk '{print $NF}'
./usr/share/man/man1/yade-batch.1.gz
./usr/share/man/man1/yade.1.gz

Read the man page yade.1.gz (without downloading the deb):

man <(dpkg-deb --fsys-tarfile <(curl -sL -o- http://httpredir.debian.org/debian/pool/main/y/yade/yade_2016.06a-7_amd64.deb) |tar -xO ./usr/share/man/man1/yade.1.gz)

man page is displayed correctly using man application.

apt --version --> apt 1.4~beta2 (amd64)
dpkg --version --> Debian 'dpkg' package management program version 1.18.18 (amd64).
man --version --> man 2.7.6.1
tar --version --> tar (GNU tar) 1.29
curl --version --> curl 7.51.0 (x86_64-pc-linux-gnu) libcurl/7.51.0 GnuTLS/3.5.7 zlib/1.2.8 libssh2/1.7.0 nghttp2/1.17.0 librtmp/2.3  

Alternative way by downloading deb file:
Bellow method based on classic apt-get, ar and tar should work in any distro.
deb file is downloaded in current working directory, man page is extracted and then file is removed.

pkg="$1"
apt-get download "$pkg" 2>/dev/null
debname=$(find . -name "$pkg*.deb")
datatar=$(ar t "$debname" |grep "data.tar") 
#ar t prints out the contents of the archive 

if [[ ${datatar##*.} == "gz" ]];then #extension check 
  options="z"
elif [[ ${datatar##*.} == "xz" ]];then
  options="J"
else
  echo "data.tar archive inside deb is not a gz or xz archive. Exiting"
  exit 1
fi

manpage+=($(ar p $debname $datatar | tar t"$options" |grep "man/man" |grep -vE "\/$" |awk '{print $NF}')) #tar t lists the files included in archive
man <(ar p "$debname" "$datatar" | tar xO"$options" ${manpage[@]}) 
#ar p and tar -O prints archive files / contents in stdout to be read by man
rm -f $debname #or rm -i for more control.

Using manpages.debian.org
As a third alternative, as of January 2017 somebody can use an alias / script that will pull the man page from debian nline, based on the fresh new debian manpages website which jumps you directly to the correct / most recent man page of the package you want:

alias debman='function __debman { links -dump https://manpages.debian.org/jump?q=$1 |awk "/Scroll to navigation/,0" |less; };__debman'

call it by terminal as $ debman yade