Table of Contents

1. Challenge

   Discover Available Shells, Use Privilege Elevation Commands, and View and Manipulate User History

   See what shells are available in the environment

   cat /etc/shells
   

   Determine what shell we're using:

   set | grep SHELL
   

   Find our user ID, group ID, and groups we're secondary members of:

   id
   

   Elevate privileges and run id:

   sudo -i id
   

   Find out who you're logged in as:

   whoami
   

   Elevate privileges and run whoami:

   sudo -i whoami
   

   View the history stack:

   history
   

   Write the history stack to a file:

   history > shell-history.txt
   

   Find the times you used whoami:

   grep -i whoami shell-history.txt
   

   Alternatively

   whoami <up arrow>
   

   run the last command

   !!
   

   run a history command by number

   !<number> ex !48
   

2. Challenge

   Explore System Variables, Create and Use Custom Variables, and Understand Special Variables

   Create a script:

   vim uservar.sh
   

   Contents

   #/bin/bash
   
   echo Hello, my name is $USER
   echo My $PRODUCT costs 10 dollars
   

   run it

   bash uservar.sh
   

   Create the $PRODUCT variable and rerun the script

   PRODUCT=Snowblower
   
   bash uservar.sh
   

   Find out which shell level we're on:

   echo $SHLVL
   

   Edit the script: At the top of the file, right below #/bin/bash, enter:

   echo Shell is at level $SHLVL
   

   Run the script again:

   bash uservar.sh
   

   We need to export the variable to make it available to the current shell:

   export PRODUCT
   

   Run the script again:

   bash uservar.sh
   

   Edit the script:

   vim uservar.sh
   

   Replace 10 dollars with $COST dollars USD. Save and quit the file. Declare a COST variable:

   export COST=100
   

   View the file's contents:

   cat uservar.sh
   

   Run the script again:

   bash uservar.sh
   

   Edit the script:

   vim uservar.sh
   

   Change the PRODUCT variable line to:

   echo "My $PRODUCT costs \$$COST dollars USD"
   

   We have to include a \ to make the $ properly show up. Save and quit. View the file's contents:

   cat uservar.sh
   

   Run the script:

   bash uservar.sh
   

   Edit the script:

   vim uservar.sh
   

   At the bottom of the file, enter:

   echo My $PRODUCT comes in $1 and I have $2 of them in stock
   
   echo The executable name is $0
   echo The arguments entered were $*
   echo The number of arguments were $#
   echo The PID of this shell is $$
   

   Here, $1 is the color of the snowblower and $2 is the amount in stock. Save and quit. View the file's contents:

   cat uservar.sh
   

   Run the script:

   bash uservar.sh
   

   Enter the arguments:

   bash uservar.sh Blue 10
   

3. Challenge

   Use Input/Output/Error Redirection to Execute Multiple Commands and Send Data to Disk

   List the files output so they're each on a separate line:

   ls -1
   

   Send the output to lsoutput.txt:

   ls -1 > lsoutput.txt
   

   Get its word count:

   wc -l lsoutput.txt
   

   View the file's contents, using it as an argument:

   cat lsoutput.txt
   

   View the file's contents, using it as an input:

   cat < lsoutput.txt
   

   The < is an input redirect.

   Pipe the output to the nl (numbered lines) command:

   cat lsoutput.txt | nl
   

   This has each item on its own numbered line.

   Pipe the output to the nl and tac (i.e., the opposite of cat) commands:

   cat lsoutput.txt | nl | tac
   

   This time, each item is numbered, but the list starts from the last number.

   Run the following:

   find /proc -iname "*.*"
   

   We'll see a lot of stdrr (Permission Denied errors).

   Put the good (or stdout) data in procdata.txt:

   find /proc -iname "*.*" > procdata.txt
   

   We'll still see all the error messages.

   View the procdata.txt file's contents:

   cat procdata.txt
   

   We should see good/stdout data.

   Send the stderr data to badprocdata.txt:

   find /proc -iname "*.*" 2> badprocdata.txt
   

   Put the stdout data in procdata.txt and get rid of the stderr data:

   find /proc -iname "*.*" > procdata.txt 2> /dev/null
   

   View the file's contents:

   cat procdata.txt
   

   Use the tee command to write the stdout data to a file and send the rest to the console:

   find /proc -iname "*.*" | tee procdata.txt
   

   Discard the stderr data and send the stdout data to the file:

   find /proc -iname "*.*" 2> /dev/null | tee procdata.txt
   

   Using a ; between commands makes them both run, no matter if one throws an error:

   ls ; farg
   

   Here, farg is not an actual command, but both commands still run.

   Using double pipes means "if the first command fails, only then run the next command." Try it:

   ls || farg
   

   Because ls worked, farg did not run.

   Switch them around:

   farg || ls
   

   Since farg failed, it had to failover to ls. Using double ampersands means "run the next command only if the first command is successful." Try it:

   ls && farg
   

   Since ls worked, it also ran farg. Reverse the order:

   farg && ls
   

   Because farg failed, ls did not run.