Difference between revisions of "Tutorial5: Redirection"

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===Main Objectives of this Practice Tutorial===
 
===Main Objectives of this Practice Tutorial===
  
:* Define the terms '''Standard Input''' ('''stdin'''), '''Standard Output''' ('''stdout'''), and '''Standard Error''' ('''stderr''')
+
:* Understand and use the '''cut''', '''tr''', and '''wc''' Linux commands
  
:* Understand the purposes of redirection symbols '''>''', '''>>''', '''2>''', '''2>>''', '''|''' and define their purpose in terms of redirection
+
:* Define the terms '''Standard Input''' (''stdin''), '''Standard Output''' (''stdout''), and '''Standard Error''' (''stderr'')
  
:* Understand the purpose of the additional file manipulation commands: '''cut''', '''tr''', and '''wc'''
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:* Understand and use the '''>''', '''>>''', '''2>''', '''2>>''' symbols with Linux commands
  
:* Define the term '''pipeline command''' and explain how a pipeline command works in terms of redirection
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:* Understand the purpose of the the '''/dev/null''' file and the '''Here Document'''
  
:* Define the term '''filter''' and how it relates to redirection using pipeline commands
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:* Define the term '''pipeline command''' and explain how a pipeline command functions
  
:* Understand how to use the '''semicolon''' symbol "''';'''" to issue multiple Unix / Linux commands
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:* Define the term '''filter''' and how it relates to pipeline commands
  
:* Understand how to use '''grouping''' using the symbols "'''( )'''" and how it is used to issue multiple Unix / Linux commands
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:* Use the '''semicolon''' ";" and '''grouping''' "( )" symbols to issue multiple Unix / Linux commands on a single line
 +
 
 +
:* Use the '''backslash''' "\" symbol to spread-out long Unix/Linux commands over multiple lines
 
<br>
 
<br>
  
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* [http://www.linfo.org/standard_output.html Standard Output (stdout)]
 
* [http://www.linfo.org/standard_output.html Standard Output (stdout)]
 
* [http://www.linfo.org/standard_error.html Standard Error (stderr)]
 
* [http://www.linfo.org/standard_error.html Standard Error (stderr)]
* [http://www.linfo.org/pipe.html Piping (pipes)]<br><br>
+
* [http://www.linfo.org/pipe.html Pipeline Commands]<br><br>
 
Multiple Commands
 
Multiple Commands
 
* [https://www.javatpoint.com/linux-semicolon Semicolon]<br>
 
* [https://www.javatpoint.com/linux-semicolon Semicolon]<br>
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= KEY CONCEPTS =
 
= KEY CONCEPTS =
 +
 +
===Additional File Manipulation Commands===
 +
 +
Before proceeding, let's look at some additional commands used to manipulate content of text files.
 +
 +
Refer to the table below regarding these text file manipulation commands:
 +
<br><br>
 +
[[Image:manipulation-commands.png|left|700px|]]
 +
<br><br><br><br><br><br><br><br><br>
  
 
===Redirection (Standard Input, Standard Output, Standard Error)===
 
===Redirection (Standard Input, Standard Output, Standard Error)===
  
''... '''standard streams''' are preconnected input and output communication channels between a computer program and its environment when it begins execution. The three input/output (I/O) connections are called '''standard input''' ('''stdin'''), '''standard output''' ('''stdout''') and '''standard error''' ('''stderr'''). Originally I/O happened via a physically connected system console (input via keyboard, output via monitor), but standard streams '''abstract''' this. When a command is executed via an interactive shell, the streams are typically connected to the text terminal on which the shell is running, but can be changed with '''redirection''' or a '''pipeline'''. ''
+
<i>'''Redirection''' can be defined as changing the way from where commands read input to where commands sends output.<br>You can redirect input and output of a command.</i>
  
Reference: https://en.wikipedia.org/wiki/Standard_streams
+
Reference: https://www.javatpoint.com/linux-input-output-redirection
  
 
[[Image:stdin-symbol.png|thumb|right|250px|The '''standard input''' ('''stdin''') symbol that describes where a Unix/Linux command receives '''input''']]
 
[[Image:stdin-symbol.png|thumb|right|250px|The '''standard input''' ('''stdin''') symbol that describes where a Unix/Linux command receives '''input''']]
'''Standard input''' ('''stdin''') is a term which describes from where a command receives input.<br>
+
'''Standard input''' ('''stdin''') is a term which describes from where a command receives '''input'''.<br>
This would apply only to Unix/Linux commands that accept stdin input (like ''cat'', ''more'', ''less'', ''sort'', ''grep'', ''head'', ''tail'', etc.).<br>
+
This would apply only to Unix/Linux commands that accept stdin input<br>(like ''cat'', ''more'', ''less'', ''sort'', ''grep'', ''head'', ''tail'', ''tr'', ''cut'', ''wc'', etc.).<br>
With the examples below, standard input is being sent into the command from the text file.
 
  
 
''Examples:''
 
''Examples:''
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<table align="right"><tr><td>[[Image:stdout-symbol-1.png|thumb|right|250px|The '''standard input''' ('''stdin''') 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''' ('''stdin''') symbol  with two greater than signs add command's output to bottom of existing file's contents.]]</td></tr></table>
+
<table align="right"><tr><td>[[Image:stdout-symbol-1.png|thumb|right|250px|The '''standard out''' ('''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 output''' ('''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 it's output.<br>In the examples below, output from a command is sent to the '''monitor''', unless it is sent to a '''regular file'''.<br>We will discuss another redirection technique called '''pipelines''' later.
+
'''Standard output''' ('''stdout''') describes where a command sends its '''output'''.<br>In the examples below, output from a command is sent to the '''monitor''', unless it is sent to a '''text file'''.
 +
 
  
 
''Examples:''
 
''Examples:''
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<span style="font-family:courier;font-weight:bold">ls -l<br>ls -l > detailed-listing.txt<br>ls /bin >> output.txt</span>
 
<span style="font-family:courier;font-weight:bold">ls -l<br>ls -l > detailed-listing.txt<br>ls /bin >> output.txt</span>
  
<table align="right"><tr><td>[[Image:stderr-symbol-1.png|thumb|right|250px|The '''standard error''' ('''sterr''') symbol with one greater than sign overwrites existing file content with command's error message.]]</td><td>[[Image:stderr-symbol-2.png|thumb|right|250px|The '''standard error''' ('''stderr''') symbol  with two greater than signs add command's error message to bottom of existing file's contents.]]</td></tr></table>
 
'''Standard Error''' ('''stderr''') describes where a command sends it's error messages.<br>In the examples below, error messages from a command are sent to a file or are redirected to a file that acts as a "garbage can".
 
  
''Examples (remember, Unix/Linux is case sensitive and issuing PWD in caps will generate an error message):''
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<table align="right"><tr><td>[[Image:stderr-symbol-1.png|thumb|right|250px|The '''standard error''' ('''sterr''') symbol with one greater than sign '''overwrites''' existing file content with command's '''error message'''.]]</td><td>[[Image:stderr-symbol-2.png|thumb|right|250px|The '''standard error''' ('''stderr''') symbol  with two greater than signs '''add''' command's error message to '''bottom''' of existing file's contents.]]</td></tr></table>
 +
'''Standard Error''' ('''stderr''') describes where a command sends it's error messages. In the examples below we issue the pwd in capitals on purpose to generate an error message, which can be redirected to a '''text file'''.
 +
 
 +
 
 +
''Examples:''
  
 
<span style="font-family:courier;font-weight:bold">PWD<br>PWD 2> error-message.txt<br>PWD 2 >> error-messages.txt<br>PWD 2> /dev/null</span>
 
<span style="font-family:courier;font-weight:bold">PWD<br>PWD 2> error-message.txt<br>PWD 2 >> error-messages.txt<br>PWD 2> /dev/null</span>
 +
<br><br>
 +
 +
====The /dev/null File====
  
  
===Additional File Manipulation Commands===
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The '''/dev/null''' file (sometimes called the '''bit bucket''' or  '''black hole''') is a special system file<br>that '''discard''' all  data written into it. This is useful to discard unwanted command output.
 +
 
 +
 
 +
''Examples:''
 +
 
 +
<span style="font-family:courier;font-weight:bold;">LS 2> /dev/null<br>ls > /dev/null<br>find / -name "tempfile" 2> /dev/null</span>
 +
<br><br>
 +
 
 +
====The Here Document====
 +
 
  
There are some additional regular file manipulation commands that you can use with redirection<br>(in addition to the other regular file manipulation commands introduced in week 2). These commands are displayed in the table below:
+
[[Image:Here Document.png|thumb|right|175px|The '''Here Document''' allows a user to redirect stdin from <u>within</u> the command itself.]]
 +
In Linux, the '''Here Document''' allows a user to redirect stdin from within the command itself.
  
<table cellpadding="5"><tr><th style="border-bottom: 1px solid black;text-align:left;">Linux Command</th><th style="border-bottom: 1px solid black;text-align:left;">Purpose</th></tr><tr valign="top"><td>'''cut'''</td><td>'''Used to extract fields and characters from records. The option '''-c''' option is used to cut by a character or a range of characters. The '''-f''' option indicates the field number or field range to display (this may require using the '''-d''' option to indicate the field separator (delimiter).'''<br><br>''Examples:''<br><span style="font-family:courier;font-weight:bold;">cut -f2 filename</span> - extract 2nd field from all records in file, using tab as delimiter (default)<br><span style="font-family:courier;font-weight:bold;">cut -d' ' -f2,5 filename</span> - extract 2nd and 5th field, using space as delimiter<br><span style="font-family:courier;font-weight:bold;">cut -d' ' -f1-3,5 filename</span> - extract 1st through 3rd and 5th fields, using space as delimiter<br><span style="font-family:courier;font-weight:bold;">cut -c3-5 filename</span> - extract 3rd to 5th characters</td></tr><tr valign="top"><td>'''tr'''</td><td>'''Used to translate characters to different characters.'''<br><br>''Examples:''<br><span style="font-family:courier;font-weight:bold;">tr a A < filename</span> - translate all characters "a" to "A"<br><span style="font-family:courier;font-weight:bold;">tr "[a-z]" "[A-Z]" < filename</span> - translate lowercase "a" through "z" to uppercase<br><span style="font-family:courier;font-weight:bold;">tr "a-z" "A-Z" < filename</span> - translate lowercase "a" through "z" to uppercase, different syntax (non-System V)<br><span style="font-family:courier;font-weight:bold;">tr ':' ' ' < filename</span> - translate all colons to spaces<br><span style="font-family:courier;font-weight:bold;">tr ' ' '\n' < filename</span>  - translate all spaces to newline characters<br><span style="font-family:courier;font-weight:bold;">tr 'abc' 'A' < filename</span> - translate 'a', 'b', and 'c' to 'A', the last character in the "to" string repeats<br></td></tr><tr valign="top"><td><span style="font-family:courier;font-weight:bold;">wc</span></td><td>'''Displays various counts of the contents of a file.'''<br><br>''Examples:''<br><span style="font-family:courier;font-weight:bold;">wc -l filename</span> - displays number of lines in file<br><span style="font-family:courier;font-weight:bold;">wc -c filename</span> - displays number of characters in file<br><span style="font-family:courier;font-weight:bold;">wc -w filename</span> - displays number of words in fil<br></td></tr></table>
+
''Example:''
  
 +
<span style="font-family:courier;font-weight:bold">cat <<+<br>Line 1<br>Line 2<br>Line 3<br>+<br><br>
  
===Piping (Using Pipes)===
+
===Pipeline Commands===
  
 
[[Image:pipe-diagram-1.png|thumb|right|450px|A '''pipeline command''' sends a command's '''standard output''' directly to '''standard input''' of other command(s) without having to create temporary files.]]
 
[[Image:pipe-diagram-1.png|thumb|right|450px|A '''pipeline command''' sends a command's '''standard output''' directly to '''standard input''' of other command(s) without having to create temporary files.]]
'''Pipeline Command:''' Having commands send their s'''tandard output''' <u>directly</u> to '''standard input''' of other  commands without having to use temporary files.
+
'''Pipeline Command:''' Having commands send their '''standard output''' <u>directly</u> to '''standard input''' of other  commands WITHOUT having to use '''temporary''' files.
  
A few simple commands can be combined to form a more powerful command line.<br>
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Pipes that are used in a '''pipeline command''' are represented by the '''pipe''' "|" symbol.<br>
  
 +
A few simple commands can be '''combined''' to form a more <u>powerful</u> command line.<br>
  
Pipes are represented by |
 
Many commands can be "piped" together, filter commands are especially useful
 
Each filter processes the initial input  based on it's design
 
Filters must be chained in a specific order, depending on what you wish to accomplish
 
Example piping use:
 
ls -al | more
 
  
Discuss pipes with the tee filter
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Commands to the '''right''' of the pipe symbol are referred to as '''filters'''. They are referred to as ''filters'' since those commands are used to '''modify''' the stdout of the <u>previous command</u>. Many commands can be "piped" together, but these commands (filters) must be chained in a specific order, depending on what you wish to accomplish
  
===Multiple Commands Using Semicolon ; / Grouping Commands ( )===
+
 
 +
''Examples:''<br>
 +
<span style="font-family:courier;font-weight:bold">ls -al | more<br>ls | sort -r<br>ls | sort | more<br>ls -l | cut -d" " -f2 | tr 'a-z' 'A-z"<br>ls | grep Linux | head -5<br>head -7 filename | tail -2</span>
 +
 
 +
====The tee Command====
 +
 
 +
 
 +
[[Image:tee-diagram-1.png|thumb|right|250px|The '''tee''' utility can be used to '''split''' the flow of information. For example to save in a file as well as display on a screen. <br>(Image licensed under [https://creativecommons.org/licenses/by-sa/3.0/ cc])]]
 +
The '''tee''' utility can be used to <u>split</u> the flow of '''standard output'''<br>between a '''text file''' and the '''terminal screen'''.<br><br>
 +
The '''tee''' option '''-a''' can be used to add content to the '''bottom''' of an existing file<br>as opposed to ''overwriting'' the file's previous contents.
 +
 
 +
The reason for the name "'''tee'''" is that the splitting of the flow of information resembles a capital T.
 +
 
 +
 
 +
''Examples:''
 +
<span style="font-family:courier;font-weight:bold">ls | tee unsorted.txt | sort<br>ls | grep Linux | tee matched.txt | more<br>ls | head -5 | tee -a listing.txt</span>
 +
<br><br>
 +
 
 +
===Multiple Commands Using Semicolon, Grouping, and Backquotes===
 
   
 
   
x
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Besides piping, there are other ways that multiple commands may be placed in one line:<br>commands may be separated by '''semi-colons'''.<br>
 +
 
 +
 
 +
''Example:''
 +
 
 +
<span style="font-family:courier;font-weight:bold">sleep 5; ls</span> 
 +
 
 +
 
 +
Multiple commands can also be '''grouped''' by using parentheses.
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 +
 
 +
''Example:''
 +
 
 +
<span style="font-family:courier;font-weight:bold">(echo "Who is on:"; w) > whoson</span><br>('''''Note:''' <u>all</u> command output is sent to a file'')
 +
 
 +
 
 +
Commands may also be '''spread-out over multiple lines''', making it easier (for humans) to interpret a long command.<br><br>
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The '''\''' symbol “''quotes-out''” the meaning of the '''ENTER''' key as <u>text</u><br> (i.e. ''new-line'' as instead of ''running'' the command).
 +
 
 +
 
 +
''Example:''
 +
 
 +
<span style="font-family:courier;font-weight:bold">echo "This will be split over multiple \<br>lines.  Note that the shell will realize \<br>that a pipe requires another command, so \<br>it will automatically go to the next line" |tr '[a-z]' '[A-Z]'</span>
 +
<br><br>
  
 
=INVESTIGATION 1: BASICS OF REDIRECTION=
 
=INVESTIGATION 1: BASICS OF REDIRECTION=
  
 
<br>
 
<br>
In this section, you will learn how to ...
+
In this section, you will learn how to redirect '''standard input''', '''standard output''' and '''standard error''' when issuing Unix / Linux commands.
 
 
 
 
  
  
 
'''Perform the Following Steps:'''
 
'''Perform the Following Steps:'''
  
# x<br><br>
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# '''Login''' to your matrix account and issue a command to '''confirm''' you are located in your '''home''' directory.<br><br>
 +
# Issue the following Linux command to create the following directory: <span style="color:blue;font-weight:bold;font-family:courier;">mkdir ~/redirect</span><br><br>
 +
# Change to the '''~/redirect''' directory and confirm that you changed to that directory.<br><br>
 +
# Use a text editor to create a file in your current directory called '''data.txt''' and enter the following text displayed below:<br><br><span style="font-family:courier;font-weight:bold">This is line 1<br>This is line 2<br>This is line 3</span><br><br>
 +
# '''Save''' editing changes and '''exit''' the text editor.<br><br>
 +
# Issue the following Linux command: <span style="color:blue;font-weight:bold;font-family:courier;">tr 'a-z' 'A-Z' < data.txt</span><br><br>What does this command do?<br><br>
 +
# Issue the following Linux command: <span style="color:blue;font-weight:bold;font-family:courier;">tr 'a-z' 'A-Z' < data.txt > output.txt</span><br><br>What does this command do? What are the contents of the file ''output.txt''?<br><br>
 +
# Issue the following Linux command: <span style="color:blue;font-weight:bold;font-family:courier;">tr 'a-z' 'A-Z' > output.txt < data.txt</span><br><br>What does this command do? Is there any difference in terms of this command and the previous command issued?<br><br>
 +
# Issue the following Linux command: <span style="color:blue;font-weight:bold;font-family:courier;">tr 'a-z' 'A-Z' >> output.txt < data.txt</span><br><br>What happens to the content of the '''output.txt''' file? Why?<br><br>
 +
# Issue the following Linux command: <span style="color:blue;font-weight:bold;font-family:courier;">tail -2 < data.txt > output.txt</span><br><br>What does this command do? Check the contents of the '''output.txt''' file to confirm.<br><br>
 +
# Issue the following Linux command: <span style="color:blue;font-weight:bold;font-family:courier;">tail -2 > output2.txt < data.txt </span><br><br>Why does this command render the same results as the previous command?<br>Try explaining how the command works in terms of '''stdin''' and then '''stdout'''.<br><br>
 +
# Issue the following Linux command to create a file: <span style="color:blue;font-weight:bold;font-family:courier;">cat > output3.txt </span><br><br>
 +
# Enter the follow text displayed below:<br><br><span style="font-family:courier;font-weight:bold;">This is the file output3.txt</span><br><br>
 +
# Press <span style="color:blue;font-weight:bold;font-family:courier;">ctrl-d</span> to exit the command.<br><br>
 +
# Issue the '''cat''' command to view the contents of the file: '''output3.txt'''<br><br>
 +
# Issue the following Linux command: <span style="color:blue;font-weight:bold;font-family:courier;">cp ~murray.saul/uli101/cars .</span><br><br>
 +
# Issue the '''cat''' command to view the contents of the '''cars''' file.<br><br>
 +
# Issue the following Linux command: <span style="color:blue;font-weight:bold;font-family:courier;">cut -c1-10 cars</span><br><br>What did this command do?<br><br>
 +
# Issue the following Linux command: <span style="color:blue;font-weight:bold;font-family:courier;">cut -f5 cars > field5.txt</span><br><br>What did this command do?<br>Check the contents in the file '''field5.txt''' to see what happened.<br><br>
 +
# Issue the following Linux command: <span style="color:blue;font-weight:bold;font-family:courier;">cut -f1-3 cars > field123.txt</span><br><br>What did this command do? (check file contents)<br><br>
 +
# Issue the following Linux command: <span style="color:blue;font-weight:bold;font-family:courier;">cut -f1,5 cars > field15.txt</span><br><br>What did this command do? (check file contents)<br><br>
 +
# Issue the following Linux command: <span style="color:blue;font-weight:bold;font-family:courier;">wc cars > count.txt</span><br><br>What information does the '''count.txt''' file contain?<br><br>
 +
# Issue the following Linux command: <span style="color:blue;font-weight:bold;font-family:courier;">wc -l cars > count1.txt</span><br><br>What information does the '''count1.txt''' file contain?<br><br>
 +
# Issue the following Linux command: <span style="color:blue;font-weight:bold;font-family:courier;">wc -w cars > count2.txt</span><br><br>What information does the '''count2.txt''' file contain?<br><br>
 +
# Issue the following Linux command: <span style="color:blue;font-weight:bold;font-family:courier;">ls -l > listing.txt</span><br><br>What information does the '''listing.txt''' file contain?<br><br>
 +
# Issue the following Linux command: <span style="color:blue;font-weight:bold;font-family:courier;">pwd > listing.txt</span><br><br>What happenned to the original contents of the file called '''listing.txt'''? Why?<br><br>
 +
# Issue the following Linux command (use 2 greater-than signs): <span style="color:blue;font-weight:bold;font-family:courier;">date >> listing.txt</span><br><br>What information does the '''listing.txt''' file contain? Why?<br><br>
 +
# Issue the following Linux command: <span style="color:blue;font-weight:bold;font-family:courier;">cat listing.txt cars > combined.txt</span><br><br>What information does the '''combined.txt''' file contain? Why?<br><br>'''NOTE''': The '''cat''' command stands for "'''concatenate'''" which means to '''combine''' contents of multiple files into a single file.<br>This is why the command is called "''cat''".<br><br>
 +
# Issue the following Linux command: <span style="color:blue;font-weight:bold;font-family:courier;">cat listing.txt cars murray 2> result.txt</span><br><br>What is displayed on the monitor? What information does the '''result.txt''' file contain? Why?<br><br>
 +
# Issue the following Linux command: <span style="color:blue;font-weight:bold;font-family:courier;">cat listing.txt cars murray > myoutput.txt 2> /dev/null</span><br><br>What is displayed on the monitor? What happened to the error message?<br><br>
 +
# Issue the following Linux command: <span style="color:blue;font-weight:bold;font-family:courier;">cat listing.txt cars murray > myoutput.txt 2> result.txt</span><br><br>What is displayed on the monitor? what do those files contain? Why?<br><br>The '''Here Document''' allows you to redirect stdin from with the Linux command itself. Let's get some practice using the Here Document.<br><br>
 +
# Issue the following Linux command:<br><span style="color:blue;font-weight:bold;font-family:courier;">cat <<+<br>line 1<br>line 2<br>line 3<br>+</span><br><br>What do you notice?<br><br>
 +
# Issue the following Linux command:<br><span style="color:blue;font-weight:bold;font-family:courier;">grep 2 <<+<br>line 1<br>line 2<br>line 3<br>+</span><br><br>What do you notice? How does this differ from the previous command? Why?<br><br>
 +
# Issue the following Linux command:<br><span style="color:blue;font-weight:bold;font-family:courier;">grep 2 > line2.txt <<+<br>line 1<br>line 2<br>line 3<br>+</span><br><br>What do you notice? What is contained in the file '''line2.txt'''? Why?<br><br>'''NOTE:''' You will now run a shell script to confirm that you properly issued Linux commands using redirection.<br><br>
 +
# Issue the following Linux command to run a checking script:<br><span style="color:blue;font-weight:bold;font-family:courier;">bash /home/murray.saul/myscripts/week5-check-1</span><br><br>
 +
# If you encounter errors, make corrections and '''re-run''' the checking script until you receive a congratulations message, then you can proceed.<br><br>
 +
# Issue the '''ls''' command to see all of the '''temporary files''' that were created as a result of redirection.<br><br>The problem with using these redirection symbols is that you create '''temporary text files''' that take up '''space''' on your file system.<br><br>
 +
# Issue a Linux command (using '''Filename Expansion''') to '''remove''' those temporary text files in the current directory.<br><br>
 +
# Issue the following Linux command to check that you removed ALL of those temporary text files:<br><span style="color:blue;font-weight:bold;font-family:courier;">bash /home/murray.saul/myscripts/week5-check-2</span><br><br>
 +
# If you encounter errors, make corrections and '''re-run''' the checking script until you receive a congratulations message, then you can proceed.<br><br>
  
In the next investigation, you will ...<br><br>
+
:In the next investigation, you will be learning how to issue '''pipeline Linux commands''' which can<br>accomplish tasks <u>without</u> creating temporary files.<br><br>
  
=INVESTIGATION 2: REDIRECTION USING PIPES =
+
=INVESTIGATION 2: REDIRECTION USING PIPELINE COMMANDS =
  
In this section, you will learn how to ...
+
In this section, you will learn to issue '''pipeline commands''' to to accomplish tasks <u>without</u> having to generate temporary files.
  
  
Line 140: Line 240:
 
'''Perform the Following Steps:'''
 
'''Perform the Following Steps:'''
  
# x<br><br>
+
# Confirm that you are still located in the '''~/redirect''' directory.<br><br>The '''problem''' with creating temporary files, is that they take up space on your server,<br>and should be removed. You actually did that in the previous investigation.<br><br>You will be issuing a '''pipeline command''' which will use the pipe symbol "|"<br>that will send the stdout from a command as stdin into another command<br><u>without</u> having to create temporary files.<br><br>
 +
# Issue the follow Linux '''pipeline command''': <span style="color:blue;font-weight:bold;font-family:courier;">ls /bin | more</span><br><br>What happened? Press '''q''' to exit display.<br><br>
 +
# Issue the following Linux '''pipeline command''': <span style="color:blue;font-weight:bold;font-family:courier;">ls /bin | who</span><br><br>What happened? Although this pipeline command provides output,<br>it '''does <u>not</u> work''' properly as a pipeline command since the '''who''' command is<br>'''NOT''' designed to accept standard input.[[Image:pipe-diagram-1.png|thumb|right|350px|]]<br><br>'''NOTE:''' When issuing pipeline commands, commands to the right of the pipe symbol must be designed to <u>accept</u> '''standard input'''. Since the ''who'' command does not, you did NOT see the contents of the '''/bin''' directory but only information relating to the ''who'' command. Therefore, the '''order''' of which you build your pipeline command and the '''type of command''' that is used as a ''filter'' is extremely important!<br><br>
 +
# Issue the following Linux command: <span style="color:blue;font-weight:bold;font-family:courier;">ls /bin/?? > listing.txt</span><br><br>
 +
# Issue the following Linux command: <span style="color:blue;font-weight:bold;font-family:courier;">sort  listing.txt</span><br><br>
 +
# Issue the following Linux command to remove the listing file: <span style="color:blue;font-weight:bold;font-family:courier;">rm listing.txt</span><br><br>
 +
# Issue the following Linux '''pipeline command''': <span style="color:blue;font-weight:bold;font-family:courier;">ls /bin/?? | sort </span><br><br>You should notice that the output from this pipeline command is the same output<br>from the command you issued in '''step #5'''.<br><br>
 +
# Issue the following Linux '''pipeline command''': <span style="color:blue;font-weight:bold;font-family:courier;">ls /bin/?? | sort | more</span><br><br>What is difference with this pipeline command as opposed to the <u>previous</u> pipeline command? Press '''q''' to exit display.<br><br>
 +
# Issue the '''ls''' command.<br><br>You should notice that '''no files have been created'''.<br>Let's get practice issuing more pipeline commands using commands<br>(previously learned or new) to be used as '''filters'''.<br><br>
 +
# Issue the following Linux '''pipeline command''': <span style="color:blue;font-weight:bold;font-family:courier;">ls /bin/?? | sort | head -5</span><br><br>What did you notice?<br><br>
 +
# Issue the following Linux '''pipeline command''': <span style="color:blue;font-weight:bold;font-family:courier;">ls /bin/???? | sort | grep r | tail -2</span><br><br>What did you notice? Could you predict the output prior to issuing this pipeline command?<br><br>
 +
# Issue the following Linux '''pipeline command''': <span style="color:blue;font-weight:bold;font-family:courier;">ls /bin/???? | sort | grep r | cut -c1-6</span><br><br>Try to explain step-by-step each process in the pipeline command (including ''filters'')<br>to explain the final output from this pipeine command.<br><br>
 +
# Confirm that you are still located in the '''~/redirect''' directory.<br><br>
 +
# Issue the following Linux '''pipeline command''':<br><span style="color:blue;font-weight:bold;font-family:courier;">ls /bin/???? | tee unsort.txt | sort | tee sort.txt | grep r | tee match.txt | head </span><br><br>
 +
# Issue the '''ls''' command to view the contents of this redirectory.<br><br>What did you notice?<br><br>
 +
# View the <u>contents</u> of the '''text files''' that were created to see how the '''tee''' command<br>was used in the previous pipeline command.<br><br>What was the purpose of using the '''tee''' command for this pipeline command?<br><br>You will now run a shell script to confirm that you properly issued that Linux pipeline command<br>using the '''tee''' command and redirection.<br><br>
 +
# Issue the following Linux command to run a checking script:<br><span style="color:blue;font-weight:bold;font-family:courier;">bash /home/murray.saul/myscripts/week5-check-3</span><br><br>If you encounter errors, make corrections and '''re-run''' the checking script until you receive<br>a congratulations message, then you can proceed.<br><br>
 +
# Change to <u>your</u> '''home''' directory.<br><br>
 +
# Remove the '''~/redirect''' directory and its contents.<br><br>
  
In the next investigation, you will ...
+
:In the next investigation, you will learn various techniques to issue '''multiple Linux commands'''<br>on the same line, or issue a '''single Linux command over multiple lines'''.
 +
<br><br>
  
=INVESTIGATION 3: MULTIPLE COMMANDS / COMMAND GROUPING =
+
=INVESTIGATION 3: ISSUING MULTIPLE UNIX/LINUX COMMANDS=
 
 
In this section, you will learn how to ...
 
  
 +
In this section, you will learn how to issue multiple Unix / Linux commands in a single line or over multiple lines.
  
  
 
'''Perform the Following Steps:'''
 
'''Perform the Following Steps:'''
  
# x<br>
+
# Confirm you are located in your '''home''' directory in your Matrix account.<br><br>
 +
# Issue the following Linux commands (using the ''semicolon'' character "''';'''" to separate <u>each</u> Linux command):<br><span style="color:blue;font-weight:bold;font-family:courier;">cal;pwd;date</span><br><br>Note the  output as well as the <u>order</u> of what each Linux command results.<br><br>
 +
# Issue the following Linux commands: <span style="color:blue;font-weight:bold;font-family:courier;">(cal;pwd;date)</span><br><br>Was there any difference in the output of this command as opposed to the previous command?<br><br>Let's see how grouping affects working with redirection.<br><br>
 +
# Issue the following Linux commands: <span style="color:blue;font-weight:bold;font-family:courier;">cal;pwd;date > output.txt</span><br><br>What happened? Where is the output for the '''date''' command?<br>Why isn't the output for the '''cal''' and '''pwd''' commands are NOT contained in that file?<br><br>
 +
# Issue a Linux command to view the contents of the file called '''output.txt'''<br><br>What do you notice?<br><br>Let's use '''grouping''' to make modification to the previous command<br><br>
 +
# Issue the following Linux commands: <span style="color:blue;font-weight:bold;font-family:courier;">(cal;pwd;date) > output.txt</span><br><br>What did you notice?<br><br>
 +
# Issue a Linux command to view the contents of the file called '''output.txt'''<br><br>What does ''grouping'' do when issuing multiple Linux commands (separated by a semi-colon ";") that uses redirection?<br><br>
 +
# Issue the following Linux pipeline command (using \ at the end of most lines):<br><span style="color:blue;font-family:courier;font-weight:bold">echo "This will be split over multiple \<br>lines.  Note that the shell will realize \<br>that a pipe requires another command, so \<br>it will automatically go to the next line" |tr '[a-z]' '[A-Z]'</span><br><br>Did the command work? What is the purpose of issuing a Linux command in this way?<br><br>
 +
# After you complete the Review Questions sections to get additional practice, then work on your '''online assignment 2'''<br>and complete '''section3''' labelled: '''Redirection and Pipes'''.
 +
<br><br>
  
 
= LINUX PRACTICE QUESTIONS =
 
= LINUX PRACTICE QUESTIONS =
Line 164: Line 291:
  
 
Your instructor may take-up these questions during class. It is up to the student to attend classes in order to obtain the answers to the following questions. Your instructor will NOT provide these answers in any other form (eg. e-mail, etc).
 
Your instructor may take-up these questions during class. It is up to the student to attend classes in order to obtain the answers to the following questions. Your instructor will NOT provide these answers in any other form (eg. e-mail, etc).
 +
 +
When answering Linux command questions, refer to the following Inverted Tree Diagram. The linux directory is contained in your home directory. Assume that you just logged into your Matrix account. Directories are <u>underlined</u>.
 +
 +
[[Image:week5-dir.png|thumb|left|300px|]]
 +
 +
<br><br><br><br><br><br><br><br><br>
  
  
 
'''Review Questions:'''
 
'''Review Questions:'''
  
# x
+
# Write a single Linux command to provide a detailed listing of all files in the '''/bin''' directory, sending the output to a file called listing.txt in the “'''projects'''” directory (append output to existing file and use a relative pathname)
# x
+
# Write a single Linux command to redirect the stderr from the command:<br>'''cat a.txt b.txt c.txt''' to a file called '''error.txt''' contained in the “'''assignments'''” directory. (overwrite previous file’s contents and use only relative pathnames)
# x
+
# Write a single Linux command: '''cat ~/a.txt ~/b.txt ~/c.txt''' and redirect stdout to a file called “good.txt” to the “tests” directory and stderr to a file called “'''bad.txt'''” to the “'''tests'''” directory. (overwrite previous contents for both files and use only relative-to-home pathnames).
# x
+
# Write a single Linux command to redirect the stdout from the command:<br>'''cat a.txt b.txt c.txt''' to a file called wrong.txt contained in the “'''projects'''” directory and throw-out any standard error messages so they don’t appear on the screen (append output to existing file and use only relative pathnames).<br><br>
# x
+
# Write a single Linux '''pipeline command''' to display a detailed listing of the '''projects''' directory but pause one screen at a time to view and navigate through all of the directory contents. Use a relative-to-home pathname.
# x
+
# Write a single Linux '''pipeline command''' to display the sorted contents (in reverse alphabetical order) of the “'''linux'''” directory. Use a relative pathname.
# x
+
# Assume that the text file called “'''.answers.txt'''” contains 10 lines. Write a single Linux pipeline command to only displays lines 5 through 8 for this file. Use only relative pathnames.
# x
+
# Write a single Linux '''pipeline command''' to only display the contents of the “'''assignments'''” directory whose filenames match the pattern “'''murray'''” (both upper or lowercase). Use an absolute pathname.
 +
# Write a single Linux '''pipeline command''' to display the number of characters contained in the file called “'''.answers.txt'''”. Use a relative-to-home pathname.
 +
# Write a single Linux '''pipeline command''' to display the number of lines contained in the file called “'''questions.txt'''”. Use a relative pathname.
 +
# Write a single Linux '''pipeline command''' to display only the first 10 characters of each filename contained in your current directory. Also, there is will be a lot of output, so also pause at each screenful so you can navigate throughout the display contents. Use a relative pathname.
 
# Create a '''table''' listing each Linux command, useful options that were mentioned in this tutorial for the following Linux commands: '''cut''' , '''tr''' , '''wc''' , and '''tee'''.
 
# Create a '''table''' listing each Linux command, useful options that were mentioned in this tutorial for the following Linux commands: '''cut''' , '''tr''' , '''wc''' , and '''tee'''.
  
  
 
[[Category:ULI101]]
 
[[Category:ULI101]]

Latest revision as of 10:35, 7 March 2021

REDIRECTION: STANDARD INPUT / STANDARD OUTPUT / STANDARD ERROR


Main Objectives of this Practice Tutorial

  • Understand and use the cut, tr, and wc Linux commands
  • Define the terms Standard Input (stdin), Standard Output (stdout), and Standard Error (stderr)
  • Understand and use the >, >>, 2>, 2>> symbols with Linux commands
  • Understand the purpose of the the /dev/null file and the Here Document
  • Define the term pipeline command and explain how a pipeline command functions
  • Define the term filter and how it relates to pipeline commands
  • Use the semicolon ";" and grouping "( )" symbols to issue multiple Unix / Linux commands on a single line
  • Use the backslash "\" symbol to spread-out long Unix/Linux commands over multiple lines


Tutorial Reference Material

Course Notes
Linux Command / Shortcut Reference
YouTube Videos
Course Notes:


Redirection

Multiple Commands

Redirection Filters Brauer Instructional Videos:

KEY CONCEPTS

Additional File Manipulation Commands

Before proceeding, let's look at some additional commands used to manipulate content of text files.

Refer to the table below regarding these text file manipulation commands:

Manipulation-commands.png










Redirection (Standard Input, Standard Output, Standard Error)

Redirection can be defined as changing the way from where commands read input to where commands sends output.
You can redirect input and output of a command.

Reference: https://www.javatpoint.com/linux-input-output-redirection

The standard input (stdin) symbol that describes where a Unix/Linux command receives input

Standard input (stdin) is a term which describes from where a command receives input.
This would apply only to Unix/Linux commands that accept stdin input
(like cat, more, less, sort, grep, head, tail, tr, cut, wc, etc.).

Examples:

tr 'a-z' 'A-Z' < words.txt
cat < abc.txt
sort < xyz.txt


The standard out (stdout) symbol with one greater than sign overwrites existing file content with command output
The standard output (stdout) symbol with two greater than signs add command's output to bottom of existing file's contents.

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.


Examples:

ls -l
ls -l > detailed-listing.txt
ls /bin >> output.txt


The standard error (sterr) symbol with one greater than sign overwrites existing file content with command's error message.
The standard error (stderr) symbol with two greater than signs add command's error message to bottom of existing file's contents.

Standard Error (stderr) describes where a command sends it's error messages. In the examples below we issue the pwd in capitals on purpose to generate an error message, which can be redirected to a text file.


Examples:

PWD
PWD 2> error-message.txt
PWD 2 >> error-messages.txt
PWD 2> /dev/null


The /dev/null File

The /dev/null file (sometimes called the bit bucket or black hole) is a special system file
that discard all data written into it. This is useful to discard unwanted command output.


Examples:

LS 2> /dev/null
ls > /dev/null
find / -name "tempfile" 2> /dev/null


The Here Document

The Here Document allows a user to redirect stdin from within the command itself.

In Linux, the Here Document allows a user to redirect stdin from within the command itself.

Example:

cat <<+
Line 1
Line 2
Line 3
+

Pipeline Commands

A pipeline command sends a command's standard output directly to standard input of other command(s) without having to create temporary files.

Pipeline Command: Having commands send their standard output directly to standard input of other commands WITHOUT having to use temporary files.

Pipes that are used in a pipeline command are represented by the pipe "|" symbol.

A few simple commands can be combined to form a more powerful command line.


Commands to the right of the pipe symbol are referred to as filters. They are referred to as filters since those commands are used to modify the stdout of the previous command. Many commands can be "piped" together, but these commands (filters) must be chained in a specific order, depending on what you wish to accomplish


Examples:
ls -al | more
ls | sort -r
ls | sort | more
ls -l | cut -d" " -f2 | tr 'a-z' 'A-z"
ls | grep Linux | head -5
head -7 filename | tail -2

The tee Command

The tee utility can be used to split the flow of information. For example to save in a file as well as display on a screen.
(Image licensed under cc)

The tee utility can be used to split the flow of standard output
between a text file and the terminal screen.

The tee option -a can be used to add content to the bottom of an existing file
as opposed to overwriting the file's previous contents.

The reason for the name "tee" is that the splitting of the flow of information resembles a capital T.


Examples: ls | tee unsorted.txt | sort
ls | grep Linux | tee matched.txt | more
ls | head -5 | tee -a listing.txt


Multiple Commands Using Semicolon, Grouping, and Backquotes

Besides piping, there are other ways that multiple commands may be placed in one line:
commands may be separated by semi-colons.


Example:

sleep 5; ls


Multiple commands can also be grouped by using parentheses.


Example:

(echo "Who is on:"; w) > whoson
(Note: all command output is sent to a file)


Commands may also be spread-out over multiple lines, making it easier (for humans) to interpret a long command.

The \ symbol “quotes-out” the meaning of the ENTER key as text
(i.e. new-line as instead of running the command).


Example:

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]'


INVESTIGATION 1: BASICS OF REDIRECTION


In this section, you will learn how to redirect standard input, standard output and standard error when issuing Unix / Linux commands.


Perform the Following Steps:

  1. Login to your matrix account and issue a command to confirm you are located in your home directory.

  2. Issue the following Linux command to create the following directory: mkdir ~/redirect

  3. Change to the ~/redirect directory and confirm that you changed to that directory.

  4. Use a text editor to create a file in your current directory called data.txt and enter the following text displayed below:

    This is line 1
    This is line 2
    This is line 3


  5. Save editing changes and exit the text editor.

  6. Issue the following Linux command: tr 'a-z' 'A-Z' < data.txt

    What does this command do?

  7. Issue the following Linux command: tr 'a-z' 'A-Z' < data.txt > output.txt

    What does this command do? What are the contents of the file output.txt?

  8. Issue the following Linux command: tr 'a-z' 'A-Z' > output.txt < data.txt

    What does this command do? Is there any difference in terms of this command and the previous command issued?

  9. Issue the following Linux command: tr 'a-z' 'A-Z' >> output.txt < data.txt

    What happens to the content of the output.txt file? Why?

  10. Issue the following Linux command: tail -2 < data.txt > output.txt

    What does this command do? Check the contents of the output.txt file to confirm.

  11. Issue the following Linux command: tail -2 > output2.txt < data.txt

    Why does this command render the same results as the previous command?
    Try explaining how the command works in terms of stdin and then stdout.

  12. Issue the following Linux command to create a file: cat > output3.txt

  13. Enter the follow text displayed below:

    This is the file output3.txt

  14. Press ctrl-d to exit the command.

  15. Issue the cat command to view the contents of the file: output3.txt

  16. Issue the following Linux command: cp ~murray.saul/uli101/cars .

  17. Issue the cat command to view the contents of the cars file.

  18. Issue the following Linux command: cut -c1-10 cars

    What did this command do?

  19. Issue the following Linux command: cut -f5 cars > field5.txt

    What did this command do?
    Check the contents in the file field5.txt to see what happened.

  20. Issue the following Linux command: cut -f1-3 cars > field123.txt

    What did this command do? (check file contents)

  21. Issue the following Linux command: cut -f1,5 cars > field15.txt

    What did this command do? (check file contents)

  22. Issue the following Linux command: wc cars > count.txt

    What information does the count.txt file contain?

  23. Issue the following Linux command: wc -l cars > count1.txt

    What information does the count1.txt file contain?

  24. Issue the following Linux command: wc -w cars > count2.txt

    What information does the count2.txt file contain?

  25. Issue the following Linux command: ls -l > listing.txt

    What information does the listing.txt file contain?

  26. Issue the following Linux command: pwd > listing.txt

    What happenned to the original contents of the file called listing.txt? Why?

  27. Issue the following Linux command (use 2 greater-than signs): date >> listing.txt

    What information does the listing.txt file contain? Why?

  28. Issue the following Linux command: cat listing.txt cars > combined.txt

    What information does the combined.txt file contain? Why?

    NOTE: The cat command stands for "concatenate" which means to combine contents of multiple files into a single file.
    This is why the command is called "cat".

  29. Issue the following Linux command: cat listing.txt cars murray 2> result.txt

    What is displayed on the monitor? What information does the result.txt file contain? Why?

  30. Issue the following Linux command: cat listing.txt cars murray > myoutput.txt 2> /dev/null

    What is displayed on the monitor? What happened to the error message?

  31. Issue the following Linux command: cat listing.txt cars murray > myoutput.txt 2> result.txt

    What is displayed on the monitor? what do those files contain? Why?

    The Here Document allows you to redirect stdin from with the Linux command itself. Let's get some practice using the Here Document.

  32. Issue the following Linux command:
    cat <<+
    line 1
    line 2
    line 3
    +


    What do you notice?

  33. 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?

  34. 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.

  35. Issue the following Linux command to run a checking script:
    bash /home/murray.saul/myscripts/week5-check-1

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

  37. 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.

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

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

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

In the next investigation, you will be learning how to issue pipeline Linux commands which can
accomplish tasks without creating temporary files.

INVESTIGATION 2: REDIRECTION USING PIPELINE COMMANDS

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


Perform the Following Steps:

  1. Confirm that you are still located in the ~/redirect directory.

    The problem with creating temporary files, is that they take up space on your server,
    and should be removed. You actually did that in the previous investigation.

    You will be issuing a pipeline command which will use the pipe symbol "|"
    that will send the stdout from a command as stdin into another command
    without having to create temporary files.

  2. Issue the follow Linux pipeline command: ls /bin | more

    What happened? Press q to exit display.

  3. Issue the following Linux pipeline command: ls /bin | who

    What happened? Although this pipeline command provides output,
    it does not work properly as a pipeline command since the who command is
    NOT designed to accept standard input.
    Pipe-diagram-1.png


    NOTE: When issuing pipeline commands, commands to the right of the pipe symbol must be designed to accept standard input. Since the who command does not, you did NOT see the contents of the /bin directory but only information relating to the who command. Therefore, the order of which you build your pipeline command and the type of command that is used as a filter is extremely important!

  4. Issue the following Linux command: ls /bin/?? > listing.txt

  5. Issue the following Linux command: sort listing.txt

  6. Issue the following Linux command to remove the listing file: rm listing.txt

  7. Issue the following Linux pipeline command: ls /bin/?? | sort

    You should notice that the output from this pipeline command is the same output
    from the command you issued in step #5.

  8. Issue the following Linux pipeline command: ls /bin/?? | sort | more

    What is difference with this pipeline command as opposed to the previous pipeline command? Press q to exit display.

  9. Issue the ls command.

    You should notice that no files have been created.
    Let's get practice issuing more pipeline commands using commands
    (previously learned or new) to be used as filters.

  10. Issue the following Linux pipeline command: ls /bin/?? | sort | head -5

    What did you notice?

  11. Issue the following Linux pipeline command: ls /bin/???? | sort | grep r | tail -2

    What did you notice? Could you predict the output prior to issuing this pipeline command?

  12. Issue the following Linux pipeline command: ls /bin/???? | sort | grep r | cut -c1-6

    Try to explain step-by-step each process in the pipeline command (including filters)
    to explain the final output from this pipeine command.

  13. Confirm that you are still located in the ~/redirect directory.

  14. Issue the following Linux pipeline command:
    ls /bin/???? | tee unsort.txt | sort | tee sort.txt | grep r | tee match.txt | head

  15. Issue the ls command to view the contents of this redirectory.

    What did you notice?

  16. 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.

  17. Issue the following Linux command to run a checking script:
    bash /home/murray.saul/myscripts/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.

  18. Change to your home directory.

  19. Remove the ~/redirect directory and its contents.

In the next investigation, you will learn various techniques to issue multiple Linux commands
on the same line, or issue a single Linux command over multiple lines.



INVESTIGATION 3: ISSUING MULTIPLE UNIX/LINUX COMMANDS

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


Perform the Following Steps:

  1. Confirm you are located in your home directory in your Matrix account.

  2. Issue the following Linux commands (using the semicolon character ";" to separate each Linux command):
    cal;pwd;date

    Note the output as well as the order of what each Linux command results.

  3. 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.

  4. 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?

  5. 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

  6. Issue the following Linux commands: (cal;pwd;date) > output.txt

    What did you notice?

  7. Issue a Linux command to view the contents of the file called output.txt

    What does grouping do when issuing multiple Linux commands (separated by a semi-colon ";") that uses redirection?

  8. 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 is the purpose of issuing a Linux command in this way?

  9. 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.



LINUX PRACTICE QUESTIONS

The purpose of this section is to obtain extra practice to help with quizzes, your midterm, and your final exam.

Here is a link to the MS Word Document of ALL of the questions displayed below but with extra room to answer on the document to simulate a quiz:

https://ict.senecacollege.ca/~murray.saul/uli101/uli101_week5_practice.docx

Your instructor may take-up these questions during class. It is up to the student to attend classes in order to obtain the answers to the following questions. Your instructor will NOT provide these answers in any other form (eg. e-mail, etc).

When answering Linux command questions, refer to the following Inverted Tree Diagram. The linux directory is contained in your home directory. Assume that you just logged into your Matrix account. Directories are underlined.

Week5-dir.png











Review Questions:

  1. Write a single Linux command to provide a detailed listing of all files in the /bin directory, sending the output to a file called listing.txt in the “projects” directory (append output to existing file and use a relative pathname)
  2. Write a single Linux command to redirect the stderr from the command:
    cat a.txt b.txt c.txt to a file called error.txt contained in the “assignments” directory. (overwrite previous file’s contents and use only relative pathnames)
  3. Write a single Linux command: cat ~/a.txt ~/b.txt ~/c.txt and redirect stdout to a file called “good.txt” to the “tests” directory and stderr to a file called “bad.txt” to the “tests” directory. (overwrite previous contents for both files and use only relative-to-home pathnames).
  4. Write a single Linux command to redirect the stdout from the command:
    cat a.txt b.txt c.txt to a file called wrong.txt contained in the “projects” directory and throw-out any standard error messages so they don’t appear on the screen (append output to existing file and use only relative pathnames).

  5. Write a single Linux pipeline command to display a detailed listing of the projects directory but pause one screen at a time to view and navigate through all of the directory contents. Use a relative-to-home pathname.
  6. Write a single Linux pipeline command to display the sorted contents (in reverse alphabetical order) of the “linux” directory. Use a relative pathname.
  7. Assume that the text file called “.answers.txt” contains 10 lines. Write a single Linux pipeline command to only displays lines 5 through 8 for this file. Use only relative pathnames.
  8. Write a single Linux pipeline command to only display the contents of the “assignments” directory whose filenames match the pattern “murray” (both upper or lowercase). Use an absolute pathname.
  9. Write a single Linux pipeline command to display the number of characters contained in the file called “.answers.txt”. Use a relative-to-home pathname.
  10. Write a single Linux pipeline command to display the number of lines contained in the file called “questions.txt”. Use a relative pathname.
  11. Write a single Linux pipeline command to display only the first 10 characters of each filename contained in your current directory. Also, there is will be a lot of output, so also pause at each screenful so you can navigate throughout the display contents. Use a relative pathname.
  12. Create a table listing each Linux command, useful options that were mentioned in this tutorial for the following Linux commands: cut , tr , wc , and tee.