Introduction to Linux in HPC/Environment variables - Revision history

Marc-andre-hermanns-bc32@rwth-aachen.de: Tweak page sorting and title

2020-12-04T15:25:10Z

Tweak page sorting and title

Marc-andre-hermanns-bc32@rwth-aachen.de: Fix DISPLAYTITLE

2020-12-04T15:02:34Z

Fix DISPLAYTITLE

Marc-andre-hermanns-bc32@rwth-aachen.de: Fit video canvas to 16:9 ratio

2020-11-23T08:49:03Z

Fit video canvas to 16:9 ratio

Robert-schade-e757@uni-paderborn.de: done

2020-11-22T14:29:01Z

done

Robert-schade-e757@uni-paderborn.de at 14:10, 22 November 2020

2020-11-22T14:10:13Z

Robert-schade-e757@uni-paderborn.de at 14:04, 22 November 2020

2020-11-22T14:04:53Z

Robert-schade-e757@uni-paderborn.de at 13:52, 22 November 2020

2020-11-22T13:52:17Z

Robert-schade-e757@uni-paderborn.de: quiz 1

2020-11-22T13:46:28Z

quiz 1

Robert-schade-e757@uni-paderborn.de: Intro

2020-11-22T13:07:29Z

Intro

Marc-andre-hermanns-bc32@rwth-aachen.de: Remove unwanted initial line breaks

2020-11-19T11:03:58Z

Remove unwanted initial line breaks

@@ Line 1: / Line 1: @@
-[[Category:Tutorials]]<nowiki />
+[[Category:Tutorials|Environment Variables (Linux)]]<nowiki />
-{{DISPLAYTITLE:Environment Variables}}<nowiki />
+{{DISPLAYTITLE:Environment Variables (Linux)}}<nowiki />
 {{Syllabus Introduction to Linux}}<nowiki />
 __TOC__

@@ Line 1: / Line 1: @@
 [[Category:Tutorials]]<nowiki />
-{{DISPLAYTITLE:<span style="position:absolute; top:-9999px;">Introduction to Linux in HPC/</span>Environment variables}}<nowiki />
+{{DISPLAYTITLE:Environment Variables}}<nowiki />
 {{Syllabus Introduction to Linux}}<nowiki />
 __TOC__

@@ Line 8: / Line 8: @@
 === Video === <!--T:5-->
-<youtube width="600" height="400" right>dAcbPeVdv0s</youtube>
+<youtube width="600" height="340" right>dAcbPeVdv0s</youtube>
 ([[Media:HPC.NRW_Introduction_to_Linux_in_HPC_10_Environment_Variables.pdf | Slides as pdf]])

@@ Line 15: / Line 15: @@
 {{hidden begin
-|title = How do you define an environment variable VARTEST and assign the value 42 to it?
+|title = How do you define an environment variable <code>VARTEST</code> and assign the value <code>42</code> to it?
 }}
 <quiz display=simple>
@@ Line 21: / Line 21: @@
 |type="()"}
 -  <code>VARTEST=42</code>
-|| Explanation: This statement would only define VARTEST as a shell variable and not as an environemnt variable.
+|| Explanation: This statement would only define <code>VARTEST</code> as a shell variable and not as an environemnt variable.
 +  <code>export VARTEST=42</code>
-|| Explanation: The keyword <code>export</code> makes VARTEST an environment variable.
+|| Explanation: The keyword <code>export</code> makes <code>VARTEST</code> an environment variable.
 -  <code>env VARTEST=42</code>
 ||
@@ Line 35: / Line 35: @@
+{
 |type="()"}
-+  <code>Use uppercase letters</code>
++  Use uppercase letters, i.e., <code>VARTEST2</code>
 || Explanation: It is recommended to only use uppercase letters, numbers, and underscores in the names of environment variables.
--  <code>Use lowercase letters</code>
+-  Use lowercase letters, i.e., <code>vartest2</code>
 ||
--  <code>There is no naming convention.</code>
+-  There is no naming convention, i.e., <code>VarTest2</code>
 ||
 </quiz>
@@ Line 60: / Line 60: @@
 {{hidden begin
-|title = What is the expected output of the following commands? <code>VARTEST="bla"; export VARTEST="BLA"; VARTEST="blub"; env | grep VARTEST </code>
+|title = What is the expected output of the following commands: <syntaxhighlight lang="bash">VARTEST="bla";export VARTEST="BLA";VARTEST="blub";env | grep VARTEST</syntaxhighlight>
 }}
 <quiz display=simple>
@@ Line 75: / Line 75: @@
 {{hidden begin
-|title = Assume that the environment variable <code>PATH</code> has the following content <code>PATH="/usr/bin:/usr/local/bin"</code>. There is a program in each directory, i.e., <code>/usr/bin/program</code> and <code>/usr/local/bin/program</code>. Which will be executed if you run <code>program</code> in the shell?
+|title = Assume that the environment variable <code>PATH</code> has the following content <code>/usr/bin:/usr/local/bin</code>. There is a program in each directory, i.e., <code>/usr/bin/program</code> and <code>/usr/local/bin/program</code>. Which will be executed if you run <code>program</code> in the shell?
 }}
 <quiz display=simple>
@@ Line 107: / Line 107: @@
-. Run the following step in a shell session
+  Run the following steps in a shell:
-    a. Define an environment variable named <code>TEST_VAR1="test1"</code>.
+. Define an environment variable named <code>TEST_VAR1="test1"</code>.
-    b. Define a shell variable names <code>TEST_VAR2="test2"</code>.
+. Define a shell variable names <code>TEST_VAR2="test2"</code>.
-    b. Make sure that <code>TEST_VAR1</code> it is in the list of environment variables.
+. Make sure that <code>TEST_VAR1</code> is in the list of environment variables.
-    c. Start a new shell session within the current session.
+. Start a new shell session within the current session.
-    d. Output the content of the two variables <code>TEST_VAR1</code> and <code>TEST_VAR2<code>.
+. Output the content of the two variables <code>TEST_VAR1</code> and <code>TEST_VAR2</code>.
-    e. Change content of the environment variable to <code>TEST_VAR1="test_new"</code>.
+. Change content of the environment variable to <code>TEST_VAR1="test_new"</code>.
-    f. Exit the shell session and output the content of <code>TEST_VAR1</code>.
+. Exit the shell session and output the content of <code>TEST_VAR1</code>.
     {| role="presentation" class="wikitable mw-collapsible mw-collapsed"
      | <strong>Answer:</strong>

@@ Line 60: / Line 60: @@
 {{hidden begin
-|title = What is the expected output of the following commands? <code>VARTEST="bla"; export VARTEST; VARTEST="blub"; env | grep VARTEST </code>
+|title = What is the expected output of the following commands? <code>VARTEST="bla"; export VARTEST="BLA"; VARTEST="blub"; env | grep VARTEST </code>
 }}
 <quiz display=simple>

@@ Line 54: / Line 54: @@
 -  An environment variable that was defined is valid and accessible in every shell session on this computer.
 ||
-+  An environment variable is valid in the shell session in which it was defined as well as all programs or shell sessions that are started from this session.
++  An environment variable is valid in the shell session in which it was defined and is inherited to all programs or shell sessions that are started from this session.
 || Explanation: Environment variables are inherited from parent processes to their child processes.
 </quiz>
@@ Line 107: / Line 107: @@
-. a. Write a script that
+. Run the following step in a shell session
-     b. Prints an environment variable
+    a. Define an environment variable named <code>TEST_VAR1="test1"</code>.
-     c. Saves the output of the date command to a variable
+    b. Define a shell variable names <code>TEST_VAR2="test2"</code>.
-     d. Sleeps briefly
+     b. Make sure that <code>TEST_VAR1</code> it is in the list of environment variables.
-     e. Prints the new and old date and time
+     c. Start a new shell session within the current session.
     {| role="presentation" class="wikitable mw-collapsible mw-collapsed"
      | <strong>Answer:</strong>
      |-
+     |
-       One possible way to write the script is
+       The commands to enter are:
        <syntaxhighlight lang="bash">
-       #!/bin/bash
+       export TEST_VAR1="test1"
+       TEST_VAR2="test2"
-       echo "I am $USER, my home directory is $HOME"
+      env | grep TEST_VAR1
+      bash
-       olddate=$(date)
+       echo $TEST_VAR1
-       sleep 10s
+       echo $TEST_VAR2
-       echo "old date: ${olddate}"
+       export TEST_VAR1="test_new"
-       echo "new date: $(date)"
+      exit
        </syntaxhighlight>
       |}
-. What do different types of quotes (single <code>'</code> vs. double <code>"</code>) do?
 {{Tutorial Navigation

@@ Line 60: / Line 60: @@
 {{hidden begin
-|title = What is the expected output of the following commands? <code>VARTEST="bla"; export VARTEST </code>
+|title = What is the expected output of the following commands? <code>VARTEST="bla"; export VARTEST; VARTEST="blub"; env | grep VARTEST </code>
 }}
 <quiz display=simple>
+{
 |type="()"}
-+  <code>var="value"</code>
+-  <code>VARTEST=""</code>
 ||
--  <code>var=="value"</code>
+-  <code>VARTEST="bla"</code>
 ||
 </quiz>
 {{hidden end}}