Linux is a multitasking operating system. This means that there are many programs running at the same time. From user perspective this means that you are able to run several programs simultaneously, and bash surely has tools to control multiple jobs execution for you. To be able to use this feature you need to learn the following commands:

1. <CTRL>+z — place currently running program in the background.
2. jobs — list all background programs.
3. fg — bring a program to foreground. fg takes a number which can be obtained from jobs as an argument, or brings last suspended program to foreground if called without parameters.
4. <CTRL>+c — stop execution of currently running programs at once. While I will not use it in this exercise, I must say that it may be very useful at times.

Now you will learn how to control program execution by using tools built in bash.

 1: less -S .profile
 2: <CTRL+z>
 3: less -S .bashrc
 4: <CTRL+z>
 5: less -S .bash_history
 6: <CTRL+z>
 7: jobs
 8: fg
 9: q
10: fg
11: q
12: fg
13: q
14: fg
15: jobs

user1@vm1:~$ less -S .profile
# exists.
# see /usr/share/doc/bash/examples/startup-files for
# the files are located in the bash-doc package.
 
# the default umask is set in /etc/profile; for setti
# for ssh logins, install and configure the libpam-um
#umask 022
 
# if running bash
if [ -n "$BASH_VERSION" ]; then
    # include .bashrc if it exists
    if [ -f "$HOME/.bashrc" ]; then
        . "$HOME/.bashrc"
 
[1]+  Stopped                 less -S .profile
user1@vm1:~$ less -S .bashrc
# for examples
 
# If not running interactively, don't do anything
[ -z "$PS1" ] && return
 
# don't put duplicate lines in the history. See bash(
# don't overwrite GNU Midnight Commander's setting of
HISTCONTROL=$HISTCONTROL${HISTCONTROL+:}ignoredups
# ... or force ignoredups and ignorespace
HISTCONTROL=ignoreboth
 
# append to the history file, don't overwrite it
shopt -s histappend
 
[2]+  Stopped                 less -S .bashrc
user1@vm1:~$ less -S .bash_history
echo Hello, $LOGNAME!
echo 'echo Hello, $LOGNAME!' >> .profile
cp .profile .profile.bak
tail .profile
ls -altr
history -w
ls -al
cat .profile
echo Hello, $LOGNAME!
echo 'echo Hello, $LOGNAME!' >> .profile
cp .profile .profile.bak
tail .profile
ls -altr
 
[3]+  Stopped                 less -S .bash_history
user1@vm1:~$ jobs
[1]   Stopped                 less -S .profile
[2]-  Stopped                 less -S .bashrc
[3]+  Stopped                 less -S .bash_history
user1@vm1:~$ fg
user1@vm1:~$ fg
user1@vm1:~$ fg
user1@vm1:~$ fg
-bash: fg: current: no such job
user1@vm1:~$ jobs
user1@vm1:~$

1. Opens .profile for viewing. Notice how I use -S parameter, which tells less to staring with - -chop-long-lines option enabled.
2. Suspends less.
3. Opens .bashrc for viewing.
4. Suspends less.
5. Opens .bash_history for viewing.
6. Suspends less.
7. Prints out list of suspended programs.
8. Switches to last less.
9. Quits it.
10. Switches to second less.
11. Quits it.
12. Switches to first less.
13. Quits it.
14. Tries to switch to last program. There is no programs left, but you do this is to make sure there are indeed none.
15. Prints out list of suspended programs. This is to make sure there are no background jobs by seeing that jobs prints out empty output.

1. Open man bash, search for JOB CONTROL typing /, JOB CONTROL, <ENTER>, and read it.