Changes

:* Understand the purposes of the redirection symbols '''>''', '''>>''', '''2>''', '''2>>''', and '''|''' (pipe)

:* Understand the purpose of the following file manipulation commands: the '''cut/dev/null''', '''tr''', file and the '''wcHere Document'''

<i>''... '''standard 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>

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>

<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'')

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

# 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>

# Change to your Confirm that you are still located in the '''home~/redirect''' directory and confirm that you are now in your home directory.<br><br>

# Issue the following Linux command to remove all temporary files in your ''redirect'' directory: <span style="color:blue;font-weight:bold;font-family:courier;">rm -r ~/redirect</span><br>and confirm that you have removed this directory and its contents.<br><br>'''NOTE:''' 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 commandwithout having to create temporary files.<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? Why is the result different than antipated?[[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 stdin</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;">cp ls /bin/?? > listing.txt</span><br><br>

# Issue the following Linux '''pipeline command''': <span style="color:blue;font-weight:bold;font-family:courier;">ls /bin/?? | sort -r</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 #67'''<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># 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># Issue a Linux command to view the contents of the file called '''output.txt'''<br><br>What do you notice? What did grouping the three Linux commands do?<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'''.

# 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” “'''projects'''” directory (append output to existing file and use a relative pathname)# 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” “'''assignments'''” directory. (overwrite previous file’s contents and use only relative pathnames) # 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“'''bad.txt” txt'''” to the “tests” “'''tests'''” directory. (overwrite previous contents for both files and use only relative-to-home pathnames).# 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” “'''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>

# Write a single Linux '''pipeline command''' to display the sorted contents (in reverse alphabetical order) of the “linux” “'''linux'''” directory. Use a relative pathname.

# Write a single Linux '''pipeline command''' to only display the contents of the “assignments” “'''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”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“'''questions.txt”txt'''”. Use a relative pathname.