Log in to pe15.cs.umb.edu

• Run the ssh client
  
  Connect to pe15.cs.umb.edu.

Directory for this Exercise

• Go to your ex directory

  cd  ~/it244/ex

• Create an ex21 directory
  

  mkdir  ex21

• Go to your ex21 directory
  

  cd  ex21

Brace Expansion

• Create some files using braces
  

  touch test{1,2,3,4,5}.txt

• Look at the files you just created
  

  ls test?.txt

• Create some additional files using braces
  

  touch {foo,bar,bletch}.txt

• Display all the files you created
  

  ls *.txt

Tilde, ~, Expansion

• Display the value of tilde
  

  echo ~

• Use tilde to display the address of my home directory
  

  echo ~ghoffman

• Use tilde followed by a string that is not a Unix ID
  

  echo ~xxx

  Bash cannot make any sense out of this expression, so it doesn't try.
  
  
• Use ~+ to display the address of your current directory
  

  echo ~+

• Use ~- to display the address of your previous directory
  

  echo ~-

Arithmetic Expansion

• Create two numeric variables
  

  a=3; b=6

• Display the values of these new variables
  

  echo "a = $a, b = $b"

• Use these variables in an arithmetic expression
  

  echo $(( $a + $b ))

• Use these variables in another arithmetic expression
  

  echo $(( a - b ))

  Notice that you did not need to put dollar signs ($) in front of the variable names.
• Use these variables in still another arithmetic express
  

  echo $((a*b))

  Notice that you do not need to use spaces to separate any of the elements of the expression.
• Create one last arithmetic expression
  

  echo $((b/a))

Command Substitution

• Use command substitution to see the permissions on the python executable file
  

  ls -l $(which python3)

• Use command substitution to set the value of a variable
  

  now=$(date)

• Display the value of this new variable
  

  echo $now

Pathname Expansion

• Display all files ending in ".txt"
  

  echo *.txt

• Display the "test" files created earlier
  

  echo test?.txt

• Display the first two "test" files
  

  echo test[12].txt

Bash Script for this Exercise

• Make sure you are in your ex21 directory
  

  cd  ~/it244/ex/ex21

• Create the script ex21.sh
  

  nano  ex21.sh

• Write into this file commands from the sections above
  
  Include Unix commands from the section Brace Expansion, up to and including the section Pathname Expansion.
  
• Save this file
  
  Save and quit.
• Make this scipt executable
  

  chmod 755 ex21.sh

• Run this script looking for error messages
  

  bash  ex21.sh > /dev/null

  Running ex21.sh this way will only print error messages.
  
  If you see nothing your script has no Unix errors.
  
  If you find any errors, fix them.
• Test your script
  

  ~ghoffman/it244_test/ex21.sh

  When the script asks if you are ready for more, hit Return or Enter.
• Let me check your script