Bash Labs

Lab: View environment variables

env
printenv

Lab: Viewing Environment variable values

1. View the value for the PATH variable

echo $PATH

2. View the value for the HOME variable

echo $HOME

3. View the value for the SHELL variable

echo $SHELL

4. View the value for the TERM variable

echo $TERM

5. View the value for the PPID variable

echo $PPID

6. View the value for the PS1 variable

echo $PS1

7. View the value for the USER variable

echo $USER

Lab: Setting and Unsetting Variables

1. Define a local variable called VR1:

VR1=RHEL9

2. View the value of VR1:

echo $VR1

3. Type bash at the command prompt to enter a sub-shell and then run echo $VR1 to check whether the variable is visible in the sub-shell.

echo $VR1

4. Exit out of the subshell:

exit

5. Turn VR1 into an environment variable:

export VR1

6. Type bash at the command prompt to enter a sub-shell and then run echo $VR1 to check whether the variable is visible in the sub-shell.

echo $VR1

7. Undefine this variable and erase it from the shell environment:

unset VR1

8. Define a local variable that contains a value with one or more white spaces:

VR2="I love RHEL 9"

9. Define and make the variable an environment variable at the same time:

export VR3="I love RHEL 9"

10. View local and environment variables:

set

Lab: Modify Primary Command Prompt

1. Change the value of the variable PS1 to reflect the desired information:

export PS1="< $LOGNAME on $HOSTNAME in \$PWD > " 

2. Edit the .bash_profile file for user1 and define the value exactly as it was run in Step 1.

vim .bash_profile

3. Test by logging off as user1 and logging back in. The new command prompt will be displayed.

Lab: Redirecting Standard Input

1. Have the cat command read the /etc/redhat-release file and display its content on the standard output (terminal screen):

cat < /etc/redhat-release

Lab: Redirecting Standard Output

1. Direct the ls command output to a file called ls.out:

ls > ls.out

2. Do the same thing but using file descriptors:

ls 1> ls.out

3. Activate the noclobber feature then try the redirect feature again:

set -o noclobber
ls > ls.out

4. Deactivate noclobber

set +o noclobber

5. Direct the ls command to append the output to the ls.out file instead of overwriting it:

ls >> ls.out
or
ls 1>> ls.out

Lab: Redirecting Standard Error

1. Direct the find command issued as a normal user to search for all occurrences of files by the name core in the entire directory tree and sends any error messages produced to /dev/null

find / -name core -print 2> /dev/null

2. Redirect both standard output and error:

ls /usr /cdr &> outerr.out
or
ls /usr /cdr 1> outerr.out 2>&1
# means to redirect file descriptor 1 to file outerr.out as well as to file descriptor 2.

3. Same as above but append to file:

ls /usr/cdr &>> outerr.out

Lab: Show History Variables

1. View HISTFILE Variable:

echo $HISTFILE

2. View HISTSIZE variable:

echo $HISTSIZE

3. View HISTFILESIZE variable:

echo $HISTFILESIZE

Lab: History command

1. Rune history without any options:

history

2. Display 10 entries:

history 10

3. Run the 15th command in history:

!15

4. re-execute the most recent occurrence of a command that started with a particular letter or series of letters (ch for example):

!ch

5. Issue the most recent command that contained “grep”:

!?grep?

6. Remove entry 24 from history:

history -d 24

7. Repeat the last command executed:

!!

Lab: Tilde expansion

1. Display user’s home directory:

echo ~

2. Display the current directory:

echo ~+

3. Display the previous working directory:

echo ~-

4. Display user1’s home directory:

echo ~user1

5. cd into the home directory of user1 and confirm:

cd ~user1
pwd

6. cd into a subdirectory:

cd ~/Documents/

7. View directory information of the root user’s desktop:

ls -ld ~root/Desktop

Lab: Command Aliasing

1. shows all aliases that are currently set for user1:

su - user1
alias

2. Run alias as root:

alias

3. Create an alias “search” to abbreviate the find command with several switches and arguments. Enclose the entire command within single quotation marks (‘’) to ensure white spaces are taken care of. Do not leave any spaces before and after the equal sign (=).

alias search='find / -name core -exec ls -l {} \;'

4. Search with the new alias:

search

5. Create and alias by the same name as rm command but adding the -i flag:

alias rm='rm -i'

6. Run rm without using the alias:

rm file1

7. Remove the two aliases we just created:

unalias search rm

Lab: Wildcards and Metacharacters

1. List all files in the /etc directory that begin with letters “ma” and followed by any characters:

ls /etc/ma*

2. List all hidden files and directories in /home/user1:

ls -d .*

3. List all files in the /var/log directory that end in “.log”:

ls /var/log/*.log

4. List all files and directories under /var/log with exactly four characters in their names:

ls -d /var/log/????

5. Include all files and directories that begin with either of the two characters and followed by any number of characters.

ls /usr/bin/[yw]*

6. Match all directory names that begin with any letter between “m” and “o” in the /etc/systemd/system directory:

ls -d /etc/systemd/system/[m-o]*

6. Inverse results of the previous:

ls -d /etc/systemd/system/[!m-o]*

Lab: Piping

1. Pipe the output to the less command in order to view the directory listing one screenful at a time:

ls -l /etc | less

2. Run the last command and pipe the output to nl to number each line:

last | nl

3. Send the output of ls to grep for the lines that do not contain the pattern “root”. Piped again for a case-insensitive selection of all lines that exclude the pattern “dec”. Number the output, and show the last four lines on the display:

ls -l /proc | grep -v root | grep -iv dec | nl | tail -4

Lab: Quoting Mechanisms

1. Remove a file called * without deleting everything in the directory:

rm \*

2. Display $LOGNAME without expanding the LOGNAME variable:

echo '$LOGNAME'

3. Run the following with double quotes and without:

echo "$SHELL"
echo "\$PWD"
echo "'\'"

Lab: grep and regex

1. Search for the pattern “operator” in the /etc/passwd file:

grep operator /etc/passwd

2. Search for the space-separated pattern “aliases and functions” in the $HOME/.bashrc file:

grep 'aliases and functions' .bashrc

3. Search for the pattern “nologin” in the passwd file and exclude (-v) the lines in the output that contain this pattern. Add the -n switch to show the line numbers associated with the matched lines.

grep -nv nologin /etc/passwd

4. Find any duplicate entries for the root user in the passwd file. Prepend the caret sign (^) to the pattern “root” to mark the beginning of a line.

grep ^root /etc/passwd

5. Identify all users in the passwd file with bash as their primary shell.

grep bash$ /etc/passwd

6. Show the entire login.defs file but exclude all the empty lines:

grep -v ^$ /etc/login.defs

7. Perform a case-insensitive search (-i) for all the lines in the /etc/bashrc file that match the pattern “path.”

grep -i path /etc/bashrc

8. Print all the lines from the /etc/lvm/lvm.conf file that contain an exact match for a word (-w) “acce” followed by exactly two characters:

grep -w acce.. /etc/lvm/lvm.conf

9. Print all the lines from the ls command output that include either (-E) the pattern “cron” or “ly”.

ls -l /etc | grep -E 'cron|ly'

10. Show all the lines from the /etc/ssh/sshd_config file but exclude (-v) the empty lines and commented lines. Use the -e flag multiple times instead of | for either or.

sudo grep -ve ^$ -ve ^# /etc/ssh/sshd_config

11. Learn more about regex:

man 7 regex

12. Consult the grep man pages:

man grep

Lab: Managing jobs

1. Issue the jobs command with the -l switch to view all the jobs running in the background:

jobs -l

2. bring job ID 1 to the foreground and start running it:

fg %1

3. Suspend job 1 with ctrl+z and then let it run in the background:

bg %1

4. Terminate job ID 1, supply its PID (31726) to the kill command:

kill 31726

Lab: Shell Startup Files

1. View the first 10 lines of /etc/bashrc:

head /etc/bashrc

2. View the first 10 lines of /etc/profile:

head /etc/profile

3. View the directory /etc/profile.d

ls -l /etc/profile.d/

4. View .bashrc

cat ~/.bashrc

5. View .bash_profile

cat ~/.bash_profile

Lab: Customize the Command Prompt (user1)

1. Permanently customize the primary shell prompt to display “<user1@server1 in /etc >:” when this user switches into the /etc directory. The prompt should always reflect the current directory directory path.

vim ~/.bash_profile
export PS1='$USERNAME $PWD'

Lab 7-2: Redirect the Standard Input, Output, and Error (user1)

1. Run the ls command on /etc, /dvd, and /var. Have the output printed on the screen and the errors forwarded to file /tmp/ioerror.

ls /etc /dvd /var 2> /tmp/ioerror

2. Check the file after the command execution and analyze the results:

cat /tmp/ioerror