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Shell Scripting with Bash
Introduction to Shell Scripting with Bash Charles Jahnke Research Computing Services Information Services & Technology Topics for Today ● Introductions ● Basic Terminology ● How to get help ● Command-line vs. Scripting ● Variables ● Handling Arguments ● Standard I/O, Pipes, and Redirection ● Control Structures (loops and If statements) ● SCC Job Submission Example Research Computing Services Research Computing Services (RCS) A group within Information Services & Technology at Boston University provides computing, storage, and visualization resources and services to support research that has specialized or highly intensive computation, storage, bandwidth, or graphics requirements. Three Primary Services: ● Research Computation ● Research Visualization ● Research Consulting and Training Breadth of Research on the Shared Computing Cluster (SCC) Me ● Research Facilitator and Administrator ● Background in biomedical engineering, bioinformatics, and IT systems ● Offices on both CRC and BUMC ○ Most of our staff on the Charles River Campus, some dedicated to BUMC ● Contact: [email protected] You ● Who has experience programming? ● Using Linux? ● Using the Shared Computing Cluster (SCC)? Basic Terminology The Command-line The line on which commands are typed and passed to the shell. Username Hostname Current Directory [username@scc1 ~]$ Prompt Command Line (input) The Shell ● The interface between the user and the operating system ● Program that interprets and executes input ● Provides: ○ Built-in commands ○ Programming control structures ○ Environment -
Bash Crash Course + Bc + Sed + Awk∗
Bash Crash course + bc + sed + awk∗ Andrey Lukyanenko, CSE, Aalto University Fall, 2011 There are many Unix shell programs: bash, sh, csh, tcsh, ksh, etc. The comparison of those can be found on-line 1. We will primary focus on the capabilities of bash v.4 shell2. 1. Each bash script can be considered as a text file which starts with #!/bin/bash. It informs the editor or interpretor which tries to open the file, what to do with the file and how should it be treated. The special character set in the beginning #! is a magic number; check man magic and /usr/share/file/magic on existing magic numbers if interested. 2. Each script (assume you created “scriptname.sh file) can be invoked by command <dir>/scriptname.sh in console, where <dir> is absolute or relative path to the script directory, e.g., ./scriptname.sh for current directory. If it has #! as the first line it will be invoked by this command, otherwise it can be called by command bash <dir>/scriptname.sh. Notice: to call script as ./scriptname.sh it has to be executable, i.e., call command chmod 555 scriptname.sh before- hand. 3. Variable in bash can be treated as integers or strings, depending on their value. There are set of operations and rules available for them. For example: #!/bin/bash var1=123 # Assigns value 123 to var1 echo var1 # Prints ’var1’ to output echo $var1 # Prints ’123’ to output var2 =321 # Error (var2: command not found) var2= 321 # Error (321: command not found) var2=321 # Correct var3=$var2 # Assigns value 321 from var2 to var3 echo $var3 # Prints ’321’ to output -
The Linux Command Line
The Linux Command Line Fifth Internet Edition William Shotts A LinuxCommand.org Book Copyright ©2008-2019, William E. Shotts, Jr. This work is licensed under the Creative Commons Attribution-Noncommercial-No De- rivative Works 3.0 United States License. To view a copy of this license, visit the link above or send a letter to Creative Commons, PO Box 1866, Mountain View, CA 94042. A version of this book is also available in printed form, published by No Starch Press. Copies may be purchased wherever fine books are sold. No Starch Press also offers elec- tronic formats for popular e-readers. They can be reached at: https://www.nostarch.com. Linux® is the registered trademark of Linus Torvalds. All other trademarks belong to their respective owners. This book is part of the LinuxCommand.org project, a site for Linux education and advo- cacy devoted to helping users of legacy operating systems migrate into the future. You may contact the LinuxCommand.org project at http://linuxcommand.org. Release History Version Date Description 19.01A January 28, 2019 Fifth Internet Edition (Corrected TOC) 19.01 January 17, 2019 Fifth Internet Edition. 17.10 October 19, 2017 Fourth Internet Edition. 16.07 July 28, 2016 Third Internet Edition. 13.07 July 6, 2013 Second Internet Edition. 09.12 December 14, 2009 First Internet Edition. Table of Contents Introduction....................................................................................................xvi Why Use the Command Line?......................................................................................xvi -
Shell Script Getopts Example
Shell Script Getopts Example Gail is constrainedly cryoscopic after delegable Hilbert sag his parcloses illuminatingly. Gonzales often tootle irresistibly when tripersonal Giordano discomposed dissonantly and buffer her Barbarossa. Robert misdraws rompishly. Find that getopts script example we use later will contain whitespace separation with command Instantly share code, notes, and snippets. OPTARG is set to the period character found. They cease in many cases unneeded and brief fact that cartoon always press them its just like matter of personal coding style. File or directory or found. Operator precedence is used when there within five is more arguments. Typically, shell scripts use getopts to parse arguments passed to them. There did many ways to against your remedy environment. Nothing gets printed when no command line options are provided. The return status is zero unless an outcome is encountered while determining the name avid the he directory within an invalid option is supplied. The exit code will be success failure. Log in charge use details from one require these accounts. How does log lumber and cpu usage by an application? Now consider running it bore an unsupported option. No need only pass the positional parameters through to borrow external program. How can I check took a directory exists in a candy shell script? What extent its purpose? When optional, the fashion can buckle on led off additional functionality, as ugly a boolean option. In those cases, it contains a pointer to that parameter. How environment check ride a variable is set to Bash? Connect and deploy knowledge write a single location that is structured and fatigue to search. -
Research Computing and Cyberinfrastructure Team
Research Computing and CyberInfrastructure team ! Working with the Linux Shell on the CWRU HPC 31 January 2019 7 February 2019 ! Presenter Emily Dragowsky KSL Data Center RCCI Team: Roger Bielefeld, Mike Warfe, Hadrian Djohari! Brian Christian, Emily Dragowsky, Jeremy Fondran, Cal Frye,! Sanjaya Gajurel, Matt Garvey, Theresa Griegger, Cindy Martin, ! Sean Maxwell, Jeno Mozes, Nasir Yilmaz, Lee Zickel Preface: Prepare your environment • User account ! # .bashrc ## cli essentials ! if [ -t 1 ] then bind '"\e[A": history-search-backward' bind '"\e[B": history-search-forward' bind '"\eOA": history-search-backward' bind '"\eOB": history-search-forward' fi ! This is too useful to pass up! Working with Linux • Preamble • Intro Session Linux Review: Finding our way • Files & Directories: Sample work flow • Shell Commands • Pipes & Redirection • Scripting Foundations • Shell & environment variables • Control Structures • Regular expressions & text manipulation • Recap & Look Ahead Rider Cluster Components ! rider.case.edu ondemand.case.edu University Firewall ! Admin Head Nodes SLURM Science Nodes Master DMZ Resource ! Data Manager Transfer Disk Storage Nodes Batch nodes GPU nodes SMP nodes Running a job: where is it? slide from Hadrian Djohari Storing Data on the HPC table from Nasir Yilmaz How data moves across campus • Buildings on campus are each assigned to a zone. Data connections go from every building to the distribution switch at the center of the zone and from there to the data centers at Kelvin Smith Library and Crawford Hall. slide -
Programming Project #2 Due: Thursday, May 13Th, 2004, 11:59 Pm
CS155: Computer Security Spring 2004 Programming Project #2 Due: Thursday, May 13th, 2004, 11:59 pm 1 Introduction 1.1 Summary In this project, you will write Josh, the journaling operator shell. Josh is a setuid-root shell that allows users to undertake a subset of root’s capabilities. Your starting point is OSH, a minimal shell developed by Gunnar Ritter. You may work alone, or in pairs. You should not collaborate with others outside your group. You will use the Boxes system again. Remember to test your Josh in a closedbox. This as- signment specification is quite long, but much of it is intended to clarify points of confusion raised by previous years’ students. Please be sure to read it carefully before beginning to code. 1.2 The Problem As discussed in class, the classical Unix permissions model does not manage privilege delegation effectively. To perform routine administrative tasks (such as cleaning out the /tmp directory), one must possess the root password, and can therefore perform other, undesirable actions (such as reading users’ mail). This limitation manifests itself most acutely in large Unix installations, where there are typically many administrators tasked with various duties. Finer granularity of access is required for such systems, along with the ability to correctly log the important events for post-attack analysis. Various systems have been devised to overcome this limitation, and allow unprivileged users to un- dertake some subset of root’s capabilities. A commonly-used example is Sudo (http://www.sudo.ws/). We will take an approach more like that taken by OSH, the Operator Shell by Michael Neuman. -
The Linux Command Line
The Linux Command Line Second Internet Edition William E. Shotts, Jr. A LinuxCommand.org Book Copyright ©2008-2013, William E. Shotts, Jr. This work is licensed under the Creative Commons Attribution-Noncommercial-No De- rivative Works 3.0 United States License. To view a copy of this license, visit the link above or send a letter to Creative Commons, 171 Second Street, Suite 300, San Fran- cisco, California, 94105, USA. Linux® is the registered trademark of Linus Torvalds. All other trademarks belong to their respective owners. This book is part of the LinuxCommand.org project, a site for Linux education and advo- cacy devoted to helping users of legacy operating systems migrate into the future. You may contact the LinuxCommand.org project at http://linuxcommand.org. This book is also available in printed form, published by No Starch Press and may be purchased wherever fine books are sold. No Starch Press also offers this book in elec- tronic formats for most popular e-readers: http://nostarch.com/tlcl.htm Release History Version Date Description 13.07 July 6, 2013 Second Internet Edition. 09.12 December 14, 2009 First Internet Edition. 09.11 November 19, 2009 Fourth draft with almost all reviewer feedback incorporated and edited through chapter 37. 09.10 October 3, 2009 Third draft with revised table formatting, partial application of reviewers feedback and edited through chapter 18. 09.08 August 12, 2009 Second draft incorporating the first editing pass. 09.07 July 18, 2009 Completed first draft. Table of Contents Introduction....................................................................................................xvi -
1 Introduction to Shell Programming
1 Introduction to Shell Programming This lecture is prepared for beginners who wish to learn the basics of shell scripting/programming plus introduction to power tools such as awk, sed, etc. 1.1 What is Linux Shell? • In Operating System, there is special program called Shell. Shell ac- cepts your instruction or commands in English (mostly) and if its a valid command, it is passed to kernel. • Shell is a user program or it's a environment provided for user interac- tion. • Shell is an command language interpreter that executes commands read from the standard input device (keyboard) or from a file. • Shell is not part of system kernel, but uses the system kernel to execute programs, create files etc. • To find all available shells in your system type following command: $ cat /etc/shells • Note that each shell does the same job, but each understand a different command syntax and provides different built-in functions. • In MS-DOS, Shell name is COMMAND.COM which is also used for same purpose, but it's not as powerful as our Linux Shells are! • To find your current shell type following command $ echo $SHELL • To use shell (You start to use your shell as soon as you log into your system) you have to simply type commands. 1 1.2 What is Shell Script ? • Normally shells are interactive. It means shell accept command from you (via keyboard) and execute them. • But if you use command one by one (sequence of 'n' number of com- mands) , the you can store this sequence of command to text file and tell the shell to execute this text file instead of entering the commands. -
Processes in Linux/Unix
Processes in Linux/Unix A program/command when executed, a special instance is provided by the system to the process. This instance consists of all the services/resources that may be utilized by the process under execution. • Whenever a command is issued in unix/linux, it creates/starts a new process. For example, pwd when issued which is used to list the current directory location the user is in, a process starts. • Through a 5 digit ID number unix/linux keeps account of the processes, this number is call process id or pid. Each process in the system has a unique pid. • Used up pid’s can be used in again for a newer process since all the possible combinations are used. • At any point of time, no two processes with the same pid exist in the system because it is the pid that Unix uses to track each process. Initializing a process A process can be run in two ways: 1. Foreground Process : Every process when started runs in foreground by default, receives input from the keyboard and sends output to the screen. When issuing pwd command $ ls pwd Output: $ /home/geeksforgeeks/root When a command/process is running in the foreground and is taking a lot of time, no other processes can be run or started because the prompt would not be available until the program finishes processing and comes out. 2. Backround Process : It runs in the background without keyboard input and waits till keyboard input is required. Thus, other processes can be done in parallel with the process running in background since they do not have to wait for the previous process to be completed. -
What's a Script?
Linux shell scripting – “Getting started ”* David Morgan *based on chapter by the same name in Classic Shell Scripting by Robbins and Beebe What ’s a script? text file containing commands executed as a unit “command” means a body of code from somewhere from where? – the alias list, in the shell’s memory – the keywords, embedded in the shell – the functions that are in shell memory – the builtins, embedded in the shell code itself – a “binary” file, outboard to the shell 1 Precedence of selection for execution aliases keywords (a.k.a. reserved words) functions builtins files (binary executable and script) – hash table – PATH Keywords (a.k.a. reserved words) RESERVED WORDS Reserved words are words that have a special meaning to the shell. The following words are recognized as reserved when unquoted and either the first word of a simple command … or the third word of a case or for command: ! case do done elif else esac fi for function if in select then until while { } time [[ ]] bash man page 2 bash builtin executables source continue fc popd test alias declare fg printf times bg typeset getopts pushd trap bind dirs hash pwd type break disown help read ulimit builtin echo history readonly umask cd enable jobs return unalias caller eval kill set unset command exec let shift wait compgen exit local shopt complete export logout suspend * code for a bash builtin resides in file /bin/bash, along with the rest of the builtins plus the shell program as a whole. Code for a utility like ls resides in its own dedicated file /bin/ls, which holds nothing else. -
UNIX 2 Enhancing Your UNIX Skills
UNIX 2 Enhancing your UNIX Skills Workbook February 2017 Associated Workbooks: UNIX 2: Practical Exercise - 3059-2016 UNIX 2: Solution - 3060-2016 Document Number: 3133-2016 1 Contents Chapter 1. Deeper UNIX Unix 1 - Revision .............................................................................................................................1 ssh and logout ............................................................................................................................1 files, directories and pathnames ...................................................................................................1 more and nano ...........................................................................................................................1 permissions ................................................................................................................................1 lpr, enscript, lpq and lprm ............................................................................................................1 Unix 1 - Revision .............................................................................................................................2 shells ..........................................................................................................................................2 filename completion (<tab>) .........................................................................................................2 history mechanism ......................................................................................................................2 -
Linux Shell Scripting Tutorial V2.0
Linux Shell Scripting Tutorial v2.0 Written by Vivek Gite <[email protected]> and Edited By Various Contributors PDF generated using the open source mwlib toolkit. See http://code.pediapress.com/ for more information. PDF generated at: Mon, 31 May 2010 07:27:26 CET Contents Articles Linux Shell Scripting Tutorial - A Beginner's handbook:About 1 Chapter 1: Quick Introduction to Linux 4 What Is Linux 4 Who created Linux 5 Where can I download Linux 6 How do I Install Linux 6 Linux usage in everyday life 7 What is Linux Kernel 7 What is Linux Shell 8 Unix philosophy 11 But how do you use the shell 12 What is a Shell Script or shell scripting 13 Why shell scripting 14 Chapter 1 Challenges 16 Chapter 2: Getting Started With Shell Programming 17 The bash shell 17 Shell commands 19 The role of shells in the Linux environment 21 Other standard shells 23 Hello, World! Tutorial 25 Shebang 27 Shell Comments 29 Setting up permissions on a script 30 Execute a script 31 Debug a script 32 Chapter 2 Challenges 33 Chapter 3:The Shell Variables and Environment 34 Variables in shell 34 Assign values to shell variables 38 Default shell variables value 40 Rules for Naming variable name 41 Display the value of shell variables 42 Quoting 46 The export statement 49 Unset shell and environment variables 50 Getting User Input Via Keyboard 50 Perform arithmetic operations 54 Create an integer variable 56 Create the constants variable 57 Bash variable existence check 58 Customize the bash shell environments 59 Recalling command history 63 Path name expansion 65 Create and use aliases 67 The tilde expansion 69 Startup scripts 70 Using aliases 72 Changing bash prompt 73 Setting shell options 77 Setting system wide shell options 82 Chapter 3 Challenges 83 Chapter 4: Conditionals Execution (Decision Making) 84 Bash structured language constructs 84 Test command 86 If structures to execute code based on a condition 87 If.