Quality of Life¶

This chapter is a little different to the others. It is not about a tool or an operator, but about some things that can help you make it nicer to use Linux/Bash on the command line.

What’s in here¶

• We will talk about background processes, learning how to start them with & and terminate them
• We will look at some useful terminal shortcuts and their usage
• We will learn how to edit a “.bashrc” file
• We will learn about using aliases

Background processes¶

Usually, if you start some program (perhaps with an input), it will start processing it and then give the output, perhaps to screen. In many cases the terminal will then be unable to accept new commands while the processes is running. On the other hand, Linux can do multi-tasking, so how do you get to a situation where you can start another application from your terminal?

The answer to this is foreground and background processes.

Normally, the process you start in a terminal runs in the foreground and you cannot do anything else in the terminal until it completes.

With the bash feature of job control you can move processes to the background and also back to the foreground. It is also possible to start a job directly in the background.

Start a background job/process¶

This is done by adding an & at the end of the command, like this:

$ <command> <options> <input> ... & 

Example:

$ tar -zcvf mydir.tar.gz LOTS-FILE-DIR/ & 

The job keeps running in the background.

Suspend a foreground job¶

You can normally suspend a foreground job with the command CTRL-Z. When you do that the shell tells you the job is suspended and it also gives the job a job ID.

No processing happens on the job while it is suspended.

Move a foreground job to the background¶

Assume you have started a program/job, like normal, in the foreground and you want to move it to the background. The steps to do that are:

• Suspend the job with CTRL-Z to release the terminal
• Give the command bg to put the suspended job to the background
• It will then start running again, but now in the background
• You can check that it is running with the command jobs

Example:

bbrydsoe@enterprise:~$ tar -zcvf Downloads.tar.gz Downloads/
Downloads/
Downloads/IMG_20250509_211952.jpg
Downloads/add2(1).m
Downloads/lstopo_lspci(1).txt
Downloads/teamviewer_15.44.5_amd64.deb
^Z
[1]+  Stopped                 tar -zcvf Downloads.tar.gz Downloads/
bbrydsoe@enterprise:~$ bg
[1]+ tar -zcvf Downloads.tar.gz Downloads/ &
bbrydsoe@enterprise:~$ jobs
[1]+  Running                 tar -zcvf Downloads.tar.gz Downloads/ &

Move a background job to the foreground¶

To get the job running in the background back to the foreground you can give the command fg %JOBID

Example for above job:

$ fg %1

If you do not give a JOBID, then fg will assume the current suspended job.

Restart a suspended job¶

You can restart a suspended job in either:

the background:

bg %JOBID

or foreground:

fg %JOBID

Remember, you can get the JOBID with the command jobs.

Terminating a job¶

You can terminate a foreground job with CTRL-C or a background job by sending it to the foreground and then do CTRL-C.

There are other ways of killing a job, with the command kill and the process ID (PID), but we will not cover that here other than saying that you can get process IDs from ps -efH | grep <suitable string> and then kill PID or kill -9 PID if nothing else works.

Useful terminal shortcuts and their usage¶

• TAB: autocomplete a file/directory or command
• CTRL-C: kill the current foreground process
• CTRL-Z: suspend the current foreground process
• CTRL-A: move the cursor to the beginning of the line
• CTRL-E: move the cursor to the end of the line
• CTRL-L: clear the screen (same as typing clear)
• CTRL-K: delete the line after the cursor
• CTRL-Y: paste the most recent thing cut or copied
• CTRL-D: delete a character at the cursor’s position
• CTRL-U: delete the whole line
• CTRL-W: delete the word before the cursor
• CTRL-P: go to the previous command in your command history (same as “arrow up”, you can see the saved history with history)
• CTRL-N: go to the next command in your command history (same as “arrow down”)
• CTRL-R: search for a command in your command history

How to edit a “.bashrc” file¶

The file “.bashrc” is in your home directory ($HOME) and is a script file that is executed on login. It contains some configurations for the terminal session and can be used to modify how i.e. shell history, aliases, paths, and other things are configured.

First and foremost; “.bashrc” is a “hidden” file. To see those, add the flag/option -a to ls.

$ ls -a 

If you just want to see what is in it, you can use cat:

$ cat $HOME/.bashrc 

To edit it, use your favourite (command-line) editor. Here vi/vim or nano are common.

$ nano $HOME/.bashrc

Useful suggestions¶

So what should you put in the “.bashrc”? It depends on your work style of course, and what you are working with, but these are some suggestions:

• Aliases (see next part, very soon)
• Environment variables, Python environments
• PATHs and library paths to own-installed software
• Customization of the terminal
• Anything you need persistent between sessions

Examples¶

export PATH=$PATH:/home/username/OTHERSOFTWARE/bin:opt/SOFTWARE/bin

export LD_LIBRARY_PATH=$LD_LIBRARY_PATH:/home/username/OTHERSOFTWARE/lib:/opt/SOFTWARE/lib 

# Change number of commands stored in memory during running to 1000 (those you can access with arrow-up or CTRL-P)
HISTSIZE=1000

# Change number of commands stored on disk to 2000 (you can see them with "history")
HISTFILESIZE=2000

# Append to the history file, don't overwrite it**
shopt -s histappend

# make less more friendly for non-text input files**
[ -x /usr/bin/lesspipe ] && eval "$(SHELL=/bin/sh lesspipe)"

# set variable identifying the chroot you work in (used in the prompt below)**
if [ -z "${debian_chroot:-}" ] && [ -r /etc/debian_chroot ]; then
debian_chroot=$(cat /etc/debian_chroot)
fi

# set a fancy prompt (non-color, unless we know we "want" color)
case "$TERM" in
    xterm-color|*-256color) color_prompt=yes;;
esac

# If this is an xterm set the title to user@host:dir
case "$TERM" in
xterm*|rxvt*)
    PS1="\[\e]0;${debian_chroot:+($debian_chroot)}\u@\h: \w\a\]$PS1"
    ;;
*)
    ;;
esac

# enable color support of ls 
if [ -x /usr/bin/dircolors ]; then
    test -r ~/.dircolors && eval "$(dircolors -b ~/.dircolors)" || eval "$(dircolors -b)"
    alias ls='ls --color=auto'
    #alias dir='dir --color=auto'
    #alias vdir='vdir --color=auto'

    alias grep='grep --color=auto'
    alias fgrep='fgrep --color=auto'
    alias egrep='egrep --color=auto'
fi

# colored GCC warnings and errors - uncomment to use 
#export GCC_COLORS='error=01;31:warning=01;35:note=01;36:caret=01;32:locus=01:quote=01'

Aliases¶

An alias for a command means that there are two commands for the same action. The reason to make an alias is usually to get something that is shorter and/or easier to remember.

Aliases can be persistent or non-persistent.

Non-persistent aliases¶

These are aliases you just need for a short time, during that specific session. They will go away next time you logout and login, and they will not be available in another shell.

They are easy to create:

$ alias ALIASNAME="command" 

alias lah="ls -lah"   

bbrydsoe@enterprise:~/exercises/awk-qol$ lah
Command 'lah' not found, did you mean:
  command 'lha' from deb jlha-utils (0.1.6-4.1)
  command 'lha' from deb lhasa (0.3.1-4)
  command 'lsh' from deb lsh-client (2.1-13)
Try: sudo apt install <deb name>
bbrydsoe@enterprise:~/exercises/awk-qol$ alias lah="ls -lah"
bbrydsoe@enterprise:~/exercises/awk-qol$ lah
total 16K
drwxrwxr-x 2 bbrydsoe bbrydsoe 4,0K maj 26 16:15 .
drwxr-xr-x 8 bbrydsoe bbrydsoe 4,0K maj 26 19:41 ..
-rw-rw-r-- 1 bbrydsoe bbrydsoe  182 maj 26 15:43 file.dat
-rw-rw-r-- 1 bbrydsoe bbrydsoe  224 maj 26 15:45 myfile.txt

Persistent aliases¶

So what do you do if you want to keep the aliases more permanently, and can use them from session to session?

• Add them to “.bashrc”
• Possibly add them to a file you create, “.bash_aliases” and then let “.bashrc” load “.bash_aliases”

     if [ -f ~/.bash_aliases ]; then
         . ~/.bash_aliases
     fi
  

Here we are just going to add them to “.bashrc”.

Exercises¶

1. Start a job in the background with &
2. Start a job that takes some time to run. Suspend it. Send it to the background. Look that it runs. Return it to the foreground.
   • Suggestion: Make a tarball of a directory with many files in.
   • If you do not have a suitable directory, you can instead run the script slowcommand.sh in “exercises” -> “awk-qol” (make sure it is executable, chmod +x slowcommand.sh)
3. Try out several of the terminal shortcuts
4. Create a couple aliases (non-persistent) and try them out
5. Add some nice aliases to your “.bashrc”, source the “.bashrc” and try the aliases!

Summary¶