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− | == Class Description ==
| + | [[Intro to bash scripting old|old content]] has moved here. |
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− | The class: a four week course on Tues evenings covering basic and
| + | = Class Description = |
− | intermediate scripting in the bash shell. We will examine a file with about 15
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− | lines of code together each night, modify the code, run it, and come up with
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− | our own scripts. We will also get to know the "Advanced Bash
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− | Scripting Guide" [1] and the Gnu "Bash Reference Manual" [2] in some depth and
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− | learn to research and solve our own programming problems. User
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− | projects are encouraged -- bring your problems and we will solve them
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− | together!
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− | I am a fifth year Ph D student from Berkeley in Demography, writing an
| + | A six-week course on Saturdays covering basic and intermediate scripting in Bash! This course will teach you all you need to know to begin writing your own scripts. You can use these to automate system administration tasks and write your own custom commands. Scripting will give you use of the full power and flexibility of Bash. The course aims to teach a strong grasp of the basic concepts through practical examples. We will teach these one at a time, with back up exercises and notes for use outside the classroom. |
− | anthropology of a small lumber town in Oregon. I have worked as a
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− | programmer in Linux for almost 10 years, and I am currently employed
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− | part time as a software project manager at Portland State.
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− | The first class target: Oct 28, 5:00 to 6:30, 2008. I will probably have to
| + | Dates and Time: Saturdays, 1:00 - 3:00pm |
− | take off a week and delay a class in the middle of the sequence.
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− | Some helpful links to get us started:
| + | May 15, 22, (no class Memorial Day weekend, May 29) |
| + | June 5, 12, 19, 26 |
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− | http://tldp.org/HOWTO/Bash-Prog-Intro-HOWTO-5.htm
| + | Location: Free Geek Classroom |
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− | http://tldp.org/LDP/abs/html/
| + | Cost: $60 for entire series; $30 for Free Geek volunteers! |
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− | http://www.gnu.org/software/bash/manual/bashref.html
| + | To register: |
| + | Send an e-mail to: Laurel (laurel@freegeek.org) and to instructor Paul Munday (paul.munday@gmail.com) |
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− | == Class Outline ==
| + | In your email, please include the following: |
| + | * Why you want to take the class |
| + | * Other classes you have taken at Free Geek |
| + | * Your computer experience |
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− | '''Day One (2008-10-28):''' What is a "script" and what is a "variable". We will write a simple script in nano, with comments, a "shebang" line, appropriate permissions, and simple output. We work on the idea of a variable, using shell expansion to assign output to variables, interpolating variables, and exporting environment variables. We will also examine the output and input streams ("stdin", "stdout", "stderr"). We will "comment-out" code. Finally we will talk about style, including indentation, variable names, trickiness, and comment-first scripting. | + | '''Please note: The class is a sequence. Please don't register if you don't think you can attend all 6 classes. There will be more chances to learn Bash at Free Geek -- promise!''' |
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− | '''Day Two (2008-11-04):''' "For-loops", "word splitting", and printf. We will explore the for-loop in all its glory, going over lists stored in variables. This will require a discussion of how Bash automatically splits strings into words and how we can control this through quoting syntax. We will also make interesting formatting commands with the printf command.
| + | == Class Tutor == |
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− | '''Day Three (2008-11-11):''' Conditionals ("if/ then" statements). We will show how to write "if" and "case" statements, and incorporate pattern matching and "file tests" into our scripts. | + | Paul Munday. I've worked as a Linux sysadmin for 12 years as well as an IT trainer focusing on FLOSS. |
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− | '''Day Four (2008-11-25):''' File input, "while-read", and useful scripting. We will investigate how to get an input line from a file, parse it into useable pieces, and do interesting things with that data (like write a simple email "spambot").
| + | == Class Requirements == |
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− | == Class Approach ==
| + | No previous programming experience is necessary but you will need to be familiar with use of the command line/terminal (bash shell). If you have taken the basic command line for builders class this should be sufficient. |
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− | Each class period I will have a file of code that is on the wiki. We will go over it together, showing you how to look up questions using online documentation. You will type examples from this wiki page, with modifications to make your own scripts, run them from the command line, and fix bugs.
| + | = Class Outline = |
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− | == Code Listings and Class Notes ==
| + | * '''Lesson 1: First Steps & Variables'''. The first lesson covers a basic introduction to scripting: what it is, and how to write one; good scripting style and how to comment your scripts; data & strings; variables --- a first building block for scripts [http://www.gatheringstorms.org/wiki/doku.php?id=bash_course:lesson_1 Class Notes] |
− | | + | * '''Lesson 2: Math with Bash & Tests.''' The second lesson covers doing basic math with bash and introduces control structures, specifically tests (a.k.a conditionals). [http://www.gatheringstorms.org/wiki/doku.php?id=bash_course:lesson_2 Class Notes] |
− | === Every day instructions ===
| + | * '''Lesson 3 : Loops.''' More on control structures, specifically loops and how to build basic menus. [http://www.gatheringstorms.org/wiki/doku.php?id=bash_course:lesson_3 Class Notes] [http://www.gatheringstorms.org/wiki/doku.php?id=bash_course:lesson_3_exercises Sample Exercises] [http://www.gatheringstorms.org/wiki/doku.php?id=bash_course:lesson_3_answers Answers] |
− | | + | * ''Lesson 4 : Arrays and Functions'' Lesson four covers arrays, a data structure with multiple elements and functions --- a useful way to reuse code and keep it organized. [http://www.gatheringstorms.org/wiki/doku.php?id=bash_course:lesson_4 Class Notes] [http://www.gatheringstorms.org/wiki/doku.php?id=bash_course:lesson_4_exercises Sample Exercises] |
− | Each new class, make a directory classX, cd to it, and do your work there; then if you want to send yourself the files via email you have the option. Open two terminals and cd to this directory in both.
| + | * '''Lesson 5: Regular Expressions, Sed and Awk.''' Regular expressions are a handy way to match text strings, combined with sed and awk they provide a powerful way to search and edit large amounts of data. [http://www.gatheringstorms.org/wiki/doku.php?id=bash_course:lesson_5 Class Notes] |
− | | + | * '''Lesson 6: Putting it all together.''' Lesson 6 will walk through the construction of a functional and useful script, step by step, so you can learn how to put them together and how you can use them for systems administration. |
− | Each time we cover a script, open a file in your favorite editor named classX-scriptY.sh where X stands for the class (1, 2, 3, 4), and Y stands for the script we are working on in class. Type all the code in. Save the file. In your other terminal window, chmod 0700 the script, then try to run it.
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− | Each day please also open the three links above to the various pieces of bash documentation. As we have questions we will try to look up the answers here rather than relying on me. (Teach a person to fish...)
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− | | |
− | Note that this class will only cover the tip of the iceberg for Bash scripting; to learn more -- follow the bash links above, type in the code you find while you read the explanations, and experiment.
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− | | |
− | Note also that this class is a work in progress, and I might jump into the wiki to make a change to the notes or the code for next time. Feel free to suggest changes or ask questions, especially if you buy me dinner after class.
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− | | |
− | === First day -- scripts and variables ===
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− | | |
− | What is a shell script anyway? It is ...
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− | | |
− | ... a file of text ...
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− | | |
− | ... full of unix commands, variables, and control structures ...
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− | | |
− | ... that usually executes from top to bottom ...
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− | | |
− | ... using variables to hold data ...
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− | | |
− | ... and loops and conditionals to do fancy programming stuff...
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− | | |
− | ... with a way to read input and write output ...
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− | | |
− | ... that probably has some "side-effects".
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− | | |
− | Why learn shell? Old-school Unix style? Class?
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− | | |
− | ==== Script 1 ====
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− | Following just prints my name. Run it as is, but then change it to print your name.
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− | | |
− | <pre>
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− | #!/bin/bash
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− | #
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− | # script 1 wsprague@nospam.org 2008-10-29
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− | # Script just prints my name
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− | #
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− | | |
− | FIRSTNAME='Webb'
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− | LASTNAME='S.'
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− | echo "Hello, $FIRSTNAME $LASTNAME"
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− | | |
− | </pre>
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− | | |
− | Edit it by running the following: nano class1-script1.sh, then save it (ctrl-O in nano), then chmod 0700 class1-script1.sh, and run as
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− |
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− | <pre>
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− | ./class1-script1.sh
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− | </pre>
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− | | |
− | in the other terminal window.
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− | | |
− | ==== Script 2 ====
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− | | |
− | This script takes a parameter from the command line and uses it as the name: "variable expansion". Note the expansion, but also how different quotes or lack thereof have different effects.
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− | | |
− | #!/bin/bash
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− | #
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− | # script 2 wsprague@nospam.org 2008-10-29
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− | # Prints names from command line
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− | #
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− | | |
− | NAME=$1
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− | echo "Hello, $NAME."
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− | echo 'Hello, $NAME.'
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− | echo Hello, $NAME.
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− | echo Hello, "$NAME".
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− | echo Hello, \"$NAME\".
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− | echo "Hello, ${NAME}with text."
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− | echo "Hello, $NAMEwith text."
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− | | |
− | </pre>
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− | | |
− | try from the command line:
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− | | |
− | <pre>
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− | ./class1-script2.sh
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− | ./class1-script2.sh Foobar
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− | ./class1-script2.sh "Foobar Smith" | |
− | ./class1-script2.sh Foobar Smith
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− | </pre>
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− | ==== Script 3 ====
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− | | |
− | This script does some basic math, and then outputs it using variable expansion. Check out the quoting. Also note what happens when we try to do math on weird input.
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− | | |
− | <pre>
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− | #!/bin/bash
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− | #
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− | # Script adds two numbers from command line
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− | | |
− | LEFT=$1
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− | RIGHT=$2
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− | RES=$(( $LEFT + $RIGHT ))
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− | echo $(( $LEFT + $RIGHT ))
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− | echo '$(( $LEFT + $RIGHT ))'
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− | echo "$(( $LEFT + $RIGHT ))"
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− | echo "$LEFT + $RIGHT = $RES."
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− | echo '$LEFT + $RIGHT = $RES.' # Why does this do what it does?
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− | | |
− | </pre>
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− | try from the command line:
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− | | |
− | <pre>
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− | ./class1-script3.sh 100 10
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− | ./class1-script3.sh 'one hundred' 'ten'
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− | ./class1-script3.sh 34
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− | </pre>
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− | | |
− | ==== Script 4 ====
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− | This script does some "shell expansion" using the unix command "date", | |
− | which gives a formatted string of the date; use "date --help" to see more).
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− | | |
− | <pre>
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− | #!/bin/bash
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− | #
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− | # Script 4. Script calculates the year if we give it years from now.
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− | #
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− | YEAR=$( date +'%Y' )
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− | YEARS_FORWARD=$1
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− | echo "Start at year $YEAR, finish at year $(($YEAR + $YEARS_FORWARD))"
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− | | |
− | </pre>
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− | | |
− | Try from the command line
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− | | |
− | <pre>
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− | ./class1-script4.sh | |
− | ./class1-script4.sh 10
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− | ./class1-script4.sh "ten" | |
− | </pre>
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− | | |
− | ==== Script 5 ====
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− | <pre>
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− | #!/bin/bash
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− | #
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− | # Script 5 takes a filename, strips any spaces from it, and moves the original file
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− | # to the new name.
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− | RES=$( echo $1 | sed 's/ /_/g' )
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− | echo "After stripping of spaces, \"$1\" looks like \"$RES\"" # Why do we escape the quotes here?
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− | echo mv "$1" "$RES" # try this same script without "echo" here, after touching a file with a name that you put into the parameters of the script
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− | | |
− | </pre>
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− | | |
− | Try from the command line:
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− | | |
− | <pre>
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− | touch "a file with spaces in the name"
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− | ./class1-script5.sh "a quoted filename with spaces"
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− | ./class1-script5.sh an unquoted filename with spaces
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− | ././class1-script5.sh a_filename_wo_spaces | |
− | </pre>
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− | | |
− | ==== Discussion ====
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− | | |
− | Coding style -- variable names, comments, indentation, trickiness.
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− | | |
− | Comment first design.
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− | "Commenting out" code.
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− | | |
− | === Second day -- for-loops ===
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− | | |
− | What is a for-loop? It is a bash construct that repeatedly grabs one item from a sequence of data separated by whitespace, does something with that piece of the sequence, until there is no more data.
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− | | |
− | Here is the paradigm:
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− | | |
− | <pre>
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− | for VARIABLE in SEQUENCE do;
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− | # bunch of statements in here that are done repeatedly
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− | # referencing $VARIABLE
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− | # more statements
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− | done
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− | </pre>
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− | | |
− | ==== Finger exercises ====
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− | | |
− | Edit a few files with nano, find them with ls, and delete them with rm
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− | Run the command `seq 1 10` from the command line
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− | Run the command `printf "hello %s, my name is %s, I am %i years old" Tarzan Jane 32`
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− | Run the command `factor 144` from the command line
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− | | |
− | ==== Script 0 ====
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− | | |
− | <pre>
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− | #!/bin/bash
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− | #
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− | # script 0 wsprague@nospam.org 2008-10-29
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− | # Basic for loop with seq and printf
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− | #
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− | | |
− | START=$1
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− | FINISH=$3
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− | FULL_SEQ=$( seq $START $FINISH )
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− | COUNT=0
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− | | |
− | printf "Start = %i, finish = %i\n" $START $FINISH
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− | for X in $FULL_SEQ; do
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− | echo "X is $X"
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− | COUNT=$(( $COUNT+1 ))
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− | touch "file.$X"
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− | done
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− | printf "finished working on %i files\n" $COUNT
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− | </pre>
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− | | |
− | Save this as class2.script0.sh, then chmod 0700 class2.script0.sh. Run as follows:
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− | | |
− | <pre>
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− | ./class2.script0.sh 1 10
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− | ./class2.script0.sh 4 14
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− | </pre>
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− | | |
− | Examine your directory to see the new files and their names. Those are from this script.
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− | | |
− | ==== Script 1 ====
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− | <pre>
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− | #!/bin/bash
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− | #
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− | # script 1 wsprague@nospam.org 2008-10-29
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− | # Takes a name and a number as parameters,
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− | # factors the number, touches all files "$name.$number".
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− | | |
− | NAME=$1
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− | NUMBER=$2
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− | FACTORS=$( gfactor $NUMBER| sed 's/^[0-9]*://g' )
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− | FACTORS_PRETTY=$( echo $FACTORS| sed 's/ /, /g' )
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− | TEST=1
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− | COUNT=0
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− | | |
− | printf "working on name = %s, number = %i, factors = [%s]" $NAME $NUMBER $FACTORS_PRETTY
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− | for X in $FACTORS; do
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− | TEST=$(($TEST * $ X))
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− | COUNT=$(($COUNT + 1))
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− | echo "touching $NAME.$X"
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− | touch "$NAME.$X"
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− | done
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− | echo "Finished working on $COUNT files"
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− | echo "Test: $TEST = $NUMBER?"
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− | </pre>
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− | | |
− | Run this as
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− | | |
− | <pre>
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− | ./class2.script1.sh 12
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− | </pre>
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− | | |
− | and look in your directory for the files created by this script. | |
− | | |
− | ==== Script 2 ====
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− | | |
− | <pre>
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− | #!/bin/bash
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− | #
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− | # script 2 wsprague@nospam.org 2008-10-29
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− | # Do some fancy formatting with printf,
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− | # by calculating the first 10 "orders of magnitude", and printing them
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− | | |
− | MAX=7
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− | SEQ=$( seq 1 10 $MAX)
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− | RES=1
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− | for I in $SEQ; do
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− | RES=$(( $RES * $I ))
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− | printf "%3i order = %i.\n" $I $RES # "%3i" keeps it at 3 spaces.
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− | done
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− | </pre>
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− | | |
− | Run this as
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− | | |
− | <pre>
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− | ./class2.script2.sh
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− | </pre>
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− | | |
− | ==== Script 3 ====
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− | | |
− | <pre>
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− | #!/bin/bash
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− | #
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− | # script 3 wsprague@nospam.org 2008-10-29
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− | # Generate times tables by using a nested loop.
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− | | |
− | START=$1
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− | FINISH=$2
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− | INCREMENT=1 # try changing this
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− | SEQ=$( seq $START 1 $FINISH)
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− | | |
− | # Print top row
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− | printf " "
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− | for x in $SEQ; do
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− | printf "%2i " $x
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− | done;
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− |
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− | # Fill in each row with left label and cell result
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− | for x in ; do
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− | printf "%2i| " $x
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− | for y in $( seq 1 1 12); do
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− | printf "%2i " $(( $x * $y ))
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− | echo $x
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− | done;
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− | </pre>
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− | | |
− | Run this as
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− | | |
− | <pre>
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− | ./class2.script3.sh 2 6 | |
− | </pre>
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− | | |
− | ==== Discussion ====
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− | | |
− | Debugging loops with echo statements
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− | | |
− | Precalculating things like sequences
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− | | |
− | Code style -- when to add whitespace between sections and stanzas
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− | | |
− | === Third day -- conditionals ===
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− | | |
− | <pre>
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− | | |
− | </pre>
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− | | |
− | === Fourth day -- while-read and scripting ===
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− | | |
− | <pre>
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− | | |
− | # Take each line of stdin into FOO
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− | # and do something with it
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− | C=1
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− | while read FOO ; do
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− | # files and dirs that exist in cwd
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− | if [[ -e $FOO ]]; then
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− | echo "Got existing: $FOO"
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− | fi
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− | | |
− | case $FOO in
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− | $PATTERN) echo "got a $PATTERN: $FOO";;
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− | *) echo "else" > /dev/null;;
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− | esac
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− | C=$(( $C + 1 ))
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− | done
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− | echo "Evaluated $C files"
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− | | |
− | # Nifty thing that could read a database and send out emails
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− | PSQL="/opt/local/lib/postgresql83/bin/psql"
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− | CMD=" select zcta, astext(centroid(the_geom)), 'blah blah' from zips order by zcta "
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− | $PSQL postgis_pdx_2008 -F ' ' -A -t -c "$CMD" | while read ZCTA POINT; do
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− | echo "$ZCTA: $POINT. Yippee!"
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− | done
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− | | |
− | </pre>
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| [[Category: Classes]] | | [[Category: Classes]] |