IT 244: Introduction to Linux/Unix
Class 17 Exercise, Thursday, April 15th

Log in to pe15

• Run the ssh client
  

  Use the values in the table below to connect to pe15.

  ssh configuration parameter	value
  protocol	ssh
  ssh version	2
  ssh port	22
  host	pe15.cs.umb.edu
  user name	your unix username
  Authentication method	password

  
  
• Enter your password

  A dialog box will appear on the screen into which you must type the password for your Unix account.

Directory for this Exercise

(When you are ready for me to check this exercise, please scroll back up to where you entered these commands!)

• Go to your ex directory

      cd  ~/it244/ex

• Create an ex17 directory
  

      mkdir  ex17

• Go to your ex17 directory
  

      cd  ex17

Start Up a script Session

Execute the script command, using the --flush option

    script --flush

Redirecting Standard Error

• Copy 2 text files from ~ckelly/course_files/it244_files to your ex17 directory
  

      cp  ~ckelly/course_files/it244_files/foo[12].txt  .

• Run ls to make sure the copy operation worked
  

      ls

• Run cat on foo1.txt and foo2.txt
  

      cat  foo?.txt

  When you give cat two files as arguments, it prints the first, followed by the second.
  
  
• Run cat on a file that does not exist
  

      cat  xxx.txt

  cat sends an error message to standard error, which is the terminal by default.
  
  
• Run cat on two files, one nonexistent, sending standard output to a file
  

      cat  foo1.txt xxx.txt  >  foo_xxx.txt

  The error message went to the terminal, not the file.
  
  
• Print the contents of foo_xxx.txt
  

      cat  foo_xxx.txt

  Notice that the error message was not inserted into the file.
  
  
• Run cat on two files, one nonexistent, sending standard error to a file
  

      cat  foo1.txt xxx.txt  2>  errors.txt

  Notice that the contents of the first file is displayed on the terminal, but not the error message.
  
  
• Print errors.txt
  

      cat  errors.txt

  errors.txt contains the error message that would have gone to the screen if you had not redirected standard error.
  
  
• Run cat on two files, one nonexistent, sending all output to a file
  

      cat  foo1.txt  xxx.txt  &>  everything.txt

  Noting appears on the screen.
  
  
• Print everything.txt
  

      cat  everything.txt

  Both the output and error message were redirected to the same file

Exit Your script Session

Use the exit command

    exit

You should see a confirmation message confirming that the script is finished, resulting in a file called typescript

Shell Scripts

• Create a script to keep track of the contents of your current directory
  

      nano  dir_snap.sh

• Enter the hashbang line
  

      #!/bin/bash

• Enter a comment describing what the script does
  

      #
      # This script takes periodic snapshots of the current directory and
      # sends them to a file "snapshot.log"

• Enter a blank line
  
  This makes the script more readable.
  
  
• Enter a line which will record the date
  

      date  >>  snapshot.log

  To be useful, the log file needs a date stamp.
  
  Notice that we are appending to a file, even though it doesn't exist at first.
  
  If you use the append symbol  >>  on a file that doesn't exist, that file will be created and the output sent to it.
  
  
• Enter a line which will record the current directory
  

      pwd  >> snapshot.log

• Enter a separator line
  

      echo  ------------------------  >>  snapshot.log

  This makes the file more readable.
  
  
• Enter a line to send a long listing for all files to the log file
  

      ls  -al  >>  snapshot.log

• Enter a line to send a blank line to the log file
  

      echo  >>  snapshot.log

  This will make the log more readable.
  
  
• Enter a line to show the script is finished
  

      echo sent directory listing to snapshot.log

• Save the file and exit nano
  
  
• Re-Start Your script Session Execute the script command, using both the --flush option AND the --append option
  

      script --flush --append

• Make the file executable

      chmod  755  dir_snap.sh

• Look at the permissions on the script
  

      ls  -l  dir_snap.sh

• Run the script
  

      ./dir_snap.sh

• Look at the contents of snapshot.log
  

      cat  snapshot.log

• Run the script again
  

      ./dir_snap.sh

  Notice that additional information is added to the end of the file.
  
  
• Look at the contents of snapshot.log
  

      cat  snapshot.log

Exit Your script Session

Use the exit command

    exit

You should see a confirmation message confirming that the script session is finished, resulting in a file called typescript. I will look at the typescript file, along with the other files in your directory.