Further Shell Scripting

Michael GriffithsCorporate Information and Computing ServicesThe University of SheffieldEmail m.griffiths@sheffield.ac.uk

Outline• Control Structures

– Conditional statements– Looping statements– Switch, case statements– Do While loops

• Functions• A preview of Globus

Conditional Statements – Bourne Shellif command executes successfully then

execute command elif this command executes successfully then

execute this command and execute this command

else execute default command

fi

Bourne shell condition test exampleif date | grep “Fri”then

echo “It’s Friday!” fi

if test “$1” = “Monday”then

echo “The typed argument is Monday.” fi

Testing strings or arithmetic expressions

Bourne shell string comparisons used with test• string1 = string2 Test identity• string1 !=string2 Test inequality• string Return 0 exit status is string is not null• -n string Return 0 exit status is string is not null

• -z string Return 0 exit status is string is null

Bourne shell arithmetic comparison operations used with test• int1 –eq int2 Test identity• int1 –ne int2 Test inequality• int1 –lt int2 Less than• int1 –gt int2 Greater than• int1 –le int2 Less than or equal• int1 –ge int2 Greater than or equal

Bourne shell combining tests using logical operators || (or) and && (and)

if date | grep “Fri” && test `date +’%H’` -gt 17

then

echo “It’s Friday, it’s hometime!!!”

fi

Conditional statements c-shellif (condition(s)) then

command group 1else

command group 2endif

if( -e $ifile) then nedit $ifileelse echo The file $ifile does not exist!endif

Example:

Arithmetic comparison example for the c-shell

if ( ( ($1 % 5) == 0) && ( ($1 % 3) == 0) ) then echo You entered a multiple of 3 and 5!else if( ( $1 % 5) == 0)then echo You entered a multiple of 5! else if ( ($1 % 3)== 0) then echo You entered a multiple of 3! else echo Not divisible by 3 or 5 endif endifendif

File enquiry operations with the bourne shell and c-shell

-d file Test if file is a directory-f file Test if file is not a directory-s file Test if the file has non zero length-r file Test if the file is readable-w file Test if the file is writable-x file Test if the file is executable-o file Test if the file is owned by the user-e file Test if the file exists-z file Test if the file has zero length

Looping Statements• For Loops

– Bourne shell for, in, do, done structure– C shell foreach, end structure

• Conditional loops– Bourne shell while, do, done– C shell while(condition), end

For loop – Bourne shellfor name in name_1 name_2 name_3 ….. name_n do command(s) ... done

Example: for i in 3 7

do

echo " $i * 5 is `expr $i \* 5` "

done

For loop – C shellforeach name (wordlist) command(s) ...end

Example: foreach dudfile(/home1/users/cs/*)

if (-z $dudfile || $dudfile == "core") then

rm $dudfile

endif

end

while statement - Bourne shell while this command execute successfullydo

this commandand this command

done

while test "$i" -gt 0

do

i=`expr $i - 1`

done

Example:

While – c shellwhile (condition)

statements

end

Example: while($i > 0 )

echo $i Sent to printer! #Might send the file to a printer

set i=`expr $i - 1`

end

Selecting From a List of Possibilities• Switch … case

– Bourne shell– c-shell

Switch.. Case – Bourne shellcase argument in

pattern 1) execute this command

and this

and this;;

pattern 2) execute this command

and this

and this;;

esac

Switch …case – Bourne shell example

case "$1" in

*".txt") ls "$1" && cp "$1" txt && echo "$1 moved to txt directory";;

*".tmp") ls "$1" && cp "$1" tmp && echo "$1 moved to tmp directory";;

esac

Switch … case – c-shell switch($1)

case *".txt":

ls "$1" && cp "$1" txt && echo "$1 moved to txt directory"

breaksw

case *".tmp":

ls "$1" && cp "$1" tmp && echo "$1 moved to tmp directory"

breaksw

endsw

Functions• Functions are declared at the beginning of a shell

script and take the format shown belowfunctionname(){

function script commands go here}

Functions• Functions called using the name of the function

– e.g. help

• Variables passed to a function using– calculate 3 5– The variables 3 and 5 will be passed to the function

calculate. These will be parameter $1 and $2 respectively for the function

Functions• With the exception of command line variables all

variables have global scope• Do not recognise the variables passed in from the

command line• Use Functions to increase

– reusability– Readability and ease of debugging

A Preview The Globus Toolkit – Middleware for grids

• Grid job submission– GRAM (Globus resource allocation manager)

• Resource discovery and information– GIS (Grid information service a metacomputiing directory service

using LDAP)• Secure Access

– Grid security infrastructure• File Management

– Grid ftp

Globus Examples• grid-proxy-init• globus-job-run maxima.leeds.ac.uk /bin/echo Hello

world• globus-url-copy

gsiftp://maxima.leeds.ac.uk$LEEDSHOME/$1 file:$PWD/$2

• Use globus commands to create grid shells scripts– Later on

Staging a Job• Useful for running a series of commands on a

remote node• globus-job-run maxima.leeds.ac.uk –s /path/script.sh

arguments– Script should not return an exit value

Examples• Executing UNIX commands on remote nodes• Querying Sun Grid engine on remote nodes• Starting X-Applications• Staging your shell scripts