Emacs Tramp tricks

Emacs org-mode literate programming

Emacs org-mode literate programming

Ok this is a neat thing, something that is really useful.

First lets explain the tramp, tamp is a feature in emacs which can be used to access remote files from within emacs. consider that you want to edit a file on a remote server, though since this server is solely a server, no one has even consider installing emacs and even less consider configuring it. You can access it through ssh, and as usual vi is installed, that's how I did it before. Then I came across tramp, I tried it with some luck and some failures and put it on the shelf and added it to the "CHECK IT OUT" list for some rainy day. Well, the rainy day arrived (quite quickly unfortunatly) and i started fiddling with it, and to my surprise this was awsome. This is what I've been looking for. Editing files with my local emacs on the remote machine is just awesome. Though, I must admit that the URL-parsing was a bit of a hassle. So lets explain it really simple

/connection:user@host

connection: .e.g. file,ssh,rsh,sudo and many more
user: system user name
host: host or ip.

these are the basic types…here is an example

/ssh:myname@192.168.8.1:/etc/passwd

Lets first consider using it on a local file. Usually we do C-x C-f /home/user/mytext.org , the same way we can connect to a remote machine and doing exactly the same: C-x C-f /ssh:user@192.168.8.2:~/mytext.org Its now possible to edit the file on the remote server the exact same way as it was on a local machine. Quite useful, though in my case most of the time I need to ssh into the machine, and then use sudo to become a superuser. This of course is possible using tramp, though now the url parsing becomes somewhat problematic. So lets explain it in steps. Lets first edit a localfile with "sudo".

/sudo:root:/etc/passwd

The first we want to do is to ssh into the machine, the output from that ssh session is then "piped" into sudo..

/sudo:user@host:/dir/file

when editing a local file with "sudo" you can ommit the "user@host" so that the it becomes sudo::/etc/passwd there is also a "sudoedit" connection type which is similair to sudo , however it does not keep the session running in the background , and is restricted to localhost

/sudoedit::/etc/passwd

That means that using sudo with a user and remote will actually use an ssh session together with sudo.

Tramp Combination

So far we been looking at how to use tramp solely, it is also possible to combine both e.g. ssh and sudo this is done using the "|" command. Lets do an example.

/ssh:user@192.168.8.5|sudo:root@192.168.8.5:/etc/passwd

To go even further its possible to connect to a remote machine via ssh and hop to another, and there edit a file using sudo..

/ssh:user@192.168.8.5|ssh:user@192.168.8.2|sudo:root@192.168.8.2:/etc/passwd

In other words, its possible to do all kinds of different kombination, at least in theory.

Org-mode links

Of course the above urls can be used as org-links.

E.g.

[[/ssh:user@192.168.8.5|sudo:root@192.168.8.5:/etc/passwd][edit passwd @192.168.1.5]]

But another useful org feature is using src fields creating small scripts runing on local and even remote computer.

Again lets do an example.

#+NAME: debootstrap_search
#+begin_src bash :dir /tmp :results drawer :exports results
   pacman -Ss debootstrap
#+end_src

#+RESULTS: debootstrap_search
:results:
community/debootstrap 1.0.123-1
    Bootstrap a basic Debian system
:end:

For more information on results see result and evaluation. The above code will execute pacman -Ss debootstrap on the local machine And the result will be added as a result drawer. The result has a name, so we could use another source block and use the result as input. e.g.

#+NAME: awkward
#+begin_src awk :stdin debootstrap_search
  /debootstrap/ {
    split($1,a,"/");
    print a[1],"->",a[2]
  }
#+end_src

#+RESULTS: awkward
: community -> debootstrap

In the above example I used the output from the debootstrap_search and feeded it into awk where I search for the line debootstrap , and split it up into an array.

gcc

clang

emacs

echo " Name Version URL"
for var in "${apa[@]}"; do
    pacman -Qi ${var} | awk '
      /(Name|Version|URL)\s+:/ {
      if ($1 == "URL" )
          printf "%s\n",$3;
      else if($1 == "Name" || $1 == "Version")
          printf "%s ",$3;
      }'
done

Name	Version	URL
gcc	15.1.1+r7+gf36ec88aa85a-1	https://gcc.gnu.org
clang	20.1.8-1	https://clang.llvm.org/
emacs	30.1-5	https://www.gnu.org/software/emacs/emacs.html

This time I did not use a drawer, instead I want the output as a table.

Calling source block

Re-use of is always fun, so sometimes you want to reuse something previously defined.

hostname
ip add | awk '/inet(.*)\/24/ {print $2}'
uname -a | awk '{print $3}'

echo "${in[0]},${in[1]},${in[2]}"
echo "banan,rumpa,pumba"

Now if I want to use that again, but maybe use another host, I could set the dir to that host.

#CALL: host-info[:dir /ssh:calle@192.168.1.2:/tmp]()

alarm

192.168.1.2/24

5.5.0-1-ARCH

unset apa
declare -A apa
apa['fisk']='pisk
PUSK'
apa['sump']='rump
SNUSK'
#echo $apa
echo ${apa[fisk]}
echo ${apa[sump]}

Run a docker

Ok, lets setup a docker image We use the results value, we are only intrested in the last command

Download archlinux

docker pull $name

Check docker images

Final example

What I want to do is to setup a table with all the host. For each of the host in the table I want to get the current cpu load, and then in the final table I want to have them in a graph..

Let there be a table

This table consists of all the ip addresses that I want to use The table is eassiest to create with C-| and follow the instructions

Computers
192.168.1.2
192.168.1.8
192.168.1.10

# what i want to do here is to iterate over the ip numbers and then
# call another function to perform the necessary evaluation
for ip in ${IPS[@]}; do
    echo ${ip}
done

cpu	75889	1101	19454	4501180	17824	11277	1459
cpu0	5226	8	1045	378224	576	226	278
cpu1	5144	66	2238	368145	1816	8186	109
cpu2	6164	58	1600	376439	916	292	95
cpu3	6487	103	1390	376133	1108	177	119
cpu4	6698	88	1344	376094	1113	203	77
cpu5	7036	143	1697	375146	1279	172	138
cpu6	5736	30	1141	375828	2628	199	89
cpu7	5583	78	3252	374317	1893	965	143
cpu8	7786	46	1431	373959	2078	204	61
cpu9	6980	65	1349	376175	975	170	69
cpu10	6415	225	1515	375289	1781	266	103
cpu11	6627	186	1448	375424	1655	213	172