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Tutorial5: Redirection

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<table align="right"><tr><td>[[Image:stdout-symbol-1.png|thumb|right|250px|The '''standard ~~input~~out''' ('''~~stdin~~stdout''') symbol with one greater than sign '''overwrites''' existing file content with command output]]</td><td>[[Image:stdout-symbol-2.png|thumb|right|250px|The '''standard ~~input~~output''' ('''~~stdin~~stdout''') symbol with two greater than signs '''add''' command's output to '''bottom''' of existing file's contents.]]</td></tr></table>

'''Standard output''' ('''stdout''') describes where a command sends its '''output'''. In the examples below, output from a command is sent to the '''monitor''', unless it is sent to a '''text file'''.

=INVESTIGATION 1: BASICS OF REDIRECTION=

'''ATTENTION''': Depending on your ULI101 instructor, you may be required to complete this tutorial for '''marks''' in this course. Please refer to your instructor's course notes and lecture notes regarding evaluation for this course. The due date for successfully completing this tutorial (i.e. '''tutorial 5''') is by '''Friday by midnight''' next week (i.e. '''Week 6'''). If your instructor has NOT assigned marks for completing this tutorial, you can perform it for '''practice'''. In this ~~section~~investigation, you will learn how to redirect '''standard input''', '''standard output''' and '''standard error''' when issuing Unix / Linux commands.

# Issue the following Linux command: grep 2 <<+ line 1 line 2 line 3 + What do you notice? How does this differ from the previous command? Why?

# Issue the following Linux command: grep 2 > line2.txt <<+ line 1 line 2 line 3 + What do you notice? What is contained in the file '''line2.txt'''? Why? '''NOTE:''' You will now run a shell script to confirm that you properly issued Linux commands using redirection.

# Issue the following Linux command to run a checking script: ~~bash /home/murray.saul/scripts~~~uli101/week5-check-1

# If you encounter errors, make corrections and '''re-run''' the checking script until you receive a congratulations message, then you can proceed.

# Issue the '''ls''' command to see all of the '''temporary files''' that were created as a result of redirection. The problem with using these redirection symbols is that you create '''temporary text files''' that take up '''space''' on your file system.

# Issue a Linux command (using '''Filename Expansion''') to '''remove''' those temporary text files in the current directory.

# Issue the following Linux command to check that you removed ALL of those temporary text files: ~~bash /home/murray.saul/scripts~~~uli101/week5-check-2

# If you encounter errors, make corrections and '''re-run''' the checking script until you receive a congratulations message, then you can proceed.

=INVESTIGATION 2: REDIRECTION USING PIPELINE COMMANDS =

In this ~~section~~investigation, you will learn to issue '''pipeline commands''' to to accomplish tasks without having to generate temporary files.

# Issue the '''ls''' command to view the contents of this redirectory. What did you notice?

# View the contents of the '''text files''' that were created to see how the '''tee''' command was used in the previous pipeline command. What was the purpose of using the '''tee''' command for this pipeline command? You will now run a shell script to confirm that you properly issued that Linux pipeline command using the '''tee''' command and redirection.

# Issue the following Linux command to run a checking script: ~~bash /home/murray.saul/scripts~~~uli101/week5-check-3 If you encounter errors, make corrections and '''re-run''' the checking script until you receive a congratulations message, then you can proceed.

# Change to your '''home''' directory.

# Remove the '''~/redirect''' directory and its contents.

=INVESTIGATION 3: ISSUING MULTIPLE UNIX/LINUX COMMANDS=

In this ~~section~~investigation, you will learn how to issue multiple Unix / Linux commands in a single line or over multiple lines.

'''Perform the Following Steps:'''

# Confirm you are located in your '''home''' directoryin your Matrix account. # Issue the following Linux commands (using the ''semicolon '' character "''';'''" to separate each Linux command): cal;pwd;date Note the ~~from the~~ output as well as the order of ~~how~~ what each ~~of those commands were processed~~Linux command results.

# Issue the following Linux commands: (cal;pwd;date) Was there any difference in the output of this command as opposed to the previous command? Let's see how grouping affects working with redirection.

# Issue the following Linux commands: cal;pwd;date > output.txt What happened? Where is the output for the '''date''' command? Why isn't the output for the '''cal''' and '''pwd''' commands are NOT contained in that file? # Issue a Linux command to view the contents of the file called '''output.txt''' What do you notice? Let's use '''grouping ''' to make modification to the previous command # Issue the following Linux commands: (cal;pwd;date) > output.txt What did you notice? # Issue a Linux command to view the contents of the file called '''output.txt''' What does ''grouping'' do ~~you notice? What did grouping the three~~ when issuing multiple Linux commands do(separated by a semi-colon ";") that uses redirection? # Issue the following Linux pipeline command (using \ at the end of most lines): echo "This will be split over multiple \ lines. Note that the shell will realize \ that a pipe requires another command, so \ it will automatically go to the next line" |tr '[a-z]' '[A-Z]' Did the command work? What ~~does~~ is the purpose of issuing a Linux command in this ~~command do~~way?

# After you complete the Review Questions sections to get additional practice, then work on your '''online assignment 2''' and complete '''section3''' labelled: '''Redirection and Pipes'''.

Msaul

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