View source for Tutorial5: Redirection

=REDIRECTION: STANDARD INPUT / STANDARD OUTPUT / STANDARD ERROR=
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===Main Objectives of this Practice Tutorial===

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===Tutorial Reference Material===

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|colspan="2" style="font-size:16px;font-weight:bold;border-bottom: thin solid black;border-spacing:0px;"|Course Notes<br>

|colspan="2" style="font-size:16px;font-weight:bold;border-bottom: thin solid black;border-spacing:0px;padding-left:15px;"|Linux Command/Shortcut Reference<br>

|colspan="1" style="font-size:16px;font-weight:bold;border-bottom: thin solid black;border-spacing:0px;padding-left:15px;"|YouTube Videos<br>

|- valign="top" style="padding-left:15px;"

|colspan="2" |Course Notes:<ul><li>[https://ict.senecacollege.ca/~murray.saul/uli101/ULI101-Week5.pdf PDF] | [https://ict.senecacollege.ca/~murray.saul/uli101/ULI101-Week5.pptx PPTX]</li></ul>


|  style="padding-left:15px;" |Redirection
* Standard Input (stdin)
* Standard Output (stdout)
* Standard Error (stderr)
* Piping (pipes)<br><br>
Multiple Commands
* Semicolon 
* Grouping ( )


|  style="padding-left:15px;"|Redirection Filters
* head
* tail
* sort
* grep
* cut
* tr
* wc

|colspan="1" style="padding-left:15px;" width="30%"|Brauer Instructional Videos:<ul><li>[https://www.youtube.com/watch?v=ocU34PcYn2U&list=PLU1b1f-2Oe90TuYfifnWulINjMv_Wr16N&index=4 Reading/Writing to Files<br>(echo, stdin, stdout, stderr, >, >>, 2>, cat, more, less, man, date, diff, diff -y, find, wc])<br><br></li></ul>
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= KEY CONCEPTS =

===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'''. ''

Reference: https://en.wikipedia.org/wiki/Standard_streams

[[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>
This would apply only to Unix/Linux commands that accept stdin input (like ''cat'', ''more'', ''less'', ''sort'', ''grep'', ''head'', ''tail'', etc.).<br>
With the examples below, standard input is being sent into the command from the text file.

''Examples:''

<span style="font-family:courier;font-weight:bold">tr 'a-z' 'A-Z' < words.txt<br>cat < abc.txt<br>sort < xyz.txt</span>


<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>
'''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.

''Examples:''

<span style="font-family:courier;font-weight:bold">ls -l<br>ls -l > detailed-listing.txt<br>ls /bin >> output.txt</span>

[[Image:stdin-symbol.png|thumb|right|250px|The '''standard input''' ('''stdin''') symbol that describes where a Unix/Linux command receives '''input''']]
'''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):''

<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>

===Additional File Manipulation Commands===

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:

<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>'''cut -f2 filename''' - extract 2nd field from all records in file, using tab as delimiter (default)<br>'''cut -d' ' -f2,5 filename''' - extract 2nd and 5th field, using space as delimiter<br>'''cut -d' ' -f1-3,5 filename''' - extract 1st through 3rd and 5th fields, using space as delimiter<br>'''cut -c3-5 filename''' - 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>'''tr a A < filename''' - translate all characters "a" to "A"<br>'''tr "[a-z]" "[A-Z]" < filename''' - translate lowercase "a" through "z" to uppercase<br>'''tr "a-z" "A-Z" < filename''' - translate lowercase "a" through "z" to uppercase, different syntax (non-System V)<br>'''tr ':' ' ' < filename''' - translate all colons to spaces<br>'''tr ' ' '\n' < filename'''  - translate all spaces to newline characters<br>'''tr 'abc' 'A' < filename''' - translate 'a', 'b', and 'c' to 'A', the last character in the "to" string repeats<br>tr 'a-f' '1-3' < filename       - same as: tr 'abcdef' '123333' <br></td></tr><tr valign="top"><td>'''wc'''</td><td>displays various counts of the contents of a file<br><br>''Examples:''<br>'''wc -l filename''' - displays number of lines in file<br>'''wc -c filename''' - displays number of characters in file<br>'''wc -w filename''' - displays number of words in fil<br></td></tr></table>

===Piping (Using Pipes)===

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===Multiple Commands Using Semicolon ; / Grouping Commands ( )===
 
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=INVESTIGATION 1: BASICS OF REDIRECTION=

<br>
In this section, you will learn how to ...




'''Perform the Following Steps:'''

# x<br><br>

In the next investigation, you will ...<br><br>

=INVESTIGATION 2: REDIRECTION USING PIPES =

In this section, you will learn how to ...



'''Perform the Following Steps:'''

# x<br><br>

In the next investigation, you will ...

=INVESTIGATION 3: MULTIPLE COMMANDS / COMMAND GROUPING =

In this section, you will learn how to ...



'''Perform the Following Steps:'''

# x<br>

= 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).


'''Review Questions:'''

# x
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# Create a '''table''' listing each Linux command, useful options that were mentioned in the online assignment #1 and command purpose for the following Linux commands: '''cut''' , '''tr''' , '''wc''' 


[[Category:ULI101]]