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Using UNIX Shell Scripts

Using UNIX Shell Scripts. Michael Griffiths Corporate Information and Computing Services The University of Sheffield Email m.griffiths@sheffield.ac.uk. Presentation Outline. Introduction Creating and Executing Shell Script Defining and accessing shell Variables

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Using UNIX Shell Scripts

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  1. Using UNIX Shell Scripts Michael Griffiths Corporate Information and Computing Services The University of Sheffield Email m.griffiths@sheffield.ac.uk

  2. Presentation Outline • Introduction • Creating and Executing Shell Script • Defining and accessing shell Variables • User Input during Shell Script Execution • Arithmetical operations on Shell variables • Control Structures • Defining ad Using Functions • Examples • References

  3. Introduction • What is the shell? • Types of shell • Why write shell programs?

  4. What is the shell? • Provides an Interface to the UNIX Operating System • It is a command interpreter • Built on top of the kernel • Enables users to run services provided by the UNIX OS • A series of commands

  5. Types of Shell • Bourne Shell (/bin/sh) • C Shell (/bin/csh) • Korn Shell (/bin/ksh) • Bash (Bourne Again Shell) (/bin/ksh) • T shell by default (/bin/tcsh) • Used on Titania • Enhanced C shell

  6. Shell Differences • Bourne shell has fewer interactive features • E.g. no user input • C shell • More C like in syntax and structure • Allows user input

  7. Why write shell programs? • Run tasks customised for different systems • Write programs for controlling jobs run an a system • Write scripts submitted by a scheduler

  8. Creating and Executing a Shell Script • Sample .cshrc script • Hello world script • Job submission script for SGE

  9. Sample .cshrc Shell Script #!/bin/csh #First execute the titania cshrc script. source /local/shef/cshrc setenv PATH $PATH":/opt/globus/bin" setenv GLOBUS_INSTALL_PATH /opt/globus/bin alias hi 'history' alias max 'ssh maxima.leeds.ac.uk -l wrsmg' alias sftl 'sftp wrsmg@maxima.leeds.ac.uk' alias lsx509 'ls -l /tmp/x509* | grep `whoami`' echo "Welcome to Titania `whoami`"

  10. Hello World Shell Script #!/bin/csh -f # Program 2a. Shell script illustrating the use of # labels and the goto statement. echo "Hello World! " # characters taken literally except $, ` echo "My name is `whoami`" # `` backquotes enclose executable statements goto label1 echo "Before label1" #This line is never reached and is never echoed label1: echo "After label1"

  11. Sun Grid Engine Job Submission Script Submits the job benchtest to the sun gridengine queue #!/bin/sh #First simple job script for sun grid engine. # #$ -l h_cpu=01:00:00 #$ -m be #$ -M username@shef.ac.uk #$ -cwd benchtest inputfile > msgoutputfile

  12. Shell Script Features • Program starts with #!/bin/sh • Comment lines start with # • Make code readable by including comments • Tell UNIX that a script file is executable • chmod u+x scriptfilename • Execute file and get runtime output, i.e. debugging mode • sh –x scriptfilename

  13. Commenting • Identify who wrote a file and when • Identify input variables • Make code easy to read • Explain complex code sections • Version control tracking • Future modifications

  14. Use of quotation marks • ‘ ‘ Single quotes enclosed characters taken literally • ls ‘>file>’ lists the file called >file> • “ “ Double quotes enclosed characters taken literally except $ ` (backquote) and \ • echo “$SHELL” the output may be /bin/tcsh • ` ` Backquote encloses executable commands • echo “My name is `whoami` “ the output is My name is cs1mkg

  15. Define and access shell variables • c-shell • set a = hello • set maximum=20 • set b=“hello world” • bourne shell • a=hello • b=“hello world” • maximum=20 • Display a variable in the bourne and c-shell • echo $a

  16. Command line parameters • $0 Name of script • $1, $2, ….. $n 1st, 2nd 3rd command line parameter • $# Number of command line parameters

  17. User Input During Shell Script Execution • Main problem with bourne shell not very interactive there is no user input! • User input with the c-shell uses the special variable $< • Example echo "Please enter the name of the job:" set jobname=$< echo "Executing, $jobname"

  18. Arithmetical operations • c-shell set i1=10 set j1=3 @ k1 = $i1 + $j1 #Note:The space between @ and k1 is important! echo "The sum of $i1 and $j1 is $k1“ • Bourne shell # The @ operator does not work for the Bourne shell i1=2 j1=6 k1=`expr $i1 \* $j1` #Using backslash to take * operator literally echo "The multiple of $i1 and $j1 is $k1"

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