Lab 8 Shell Script Reference: Linux Shell Scripting Tutorial v1.05r3 A Beginner's handbook http://www.freeos.com/guides/lsst/index.html

Positional parameters or command line arguments Special shell variables $0…$9 Positional parameters or command line arguments myscript foo bar myscript $0 foo $1 Bar $2 $# tells you how many parameter your script was given

if condition if condition which is used for decision making in shell script, If given condition is true then command1 is executed. Syntax: if condition then command1... fi -cat command: Display text files on screen. cat file-name

test expression or [ expr ] - -True  return zero(0) Is used to see if an expression is true - -False returns nonzero Syntax: test expression OR [ expression ] $ vi ispositive # Script to see whether argument is positive # if test $1 -gt 0 then echo "$1 number is positive" fi Run it as follows: $ chmod 755 ispositive $ ./ispositive 5

test expression or [ expr ] For test statement with if commandFor [ expr ] statement with if command Mathematical Operator in  Shell Script Meaning if [ 5 -eq 6 ] if test 5 -eq 6 is equal to -eq if [ 5 -ne 6 ] if test 5 -ne 6 is not equal to -ne if [ 5 -lt 6 ] if test 5 -lt 6 is less than -lt if [ 5 -le 6 ] if test 5 -le 6 is less than or equal to -le if [ 5 -gt 6 ] if test 5 -gt 6 is greater than -gt if [ 5 -ge 6 ] if test 5 -ge 6 is greater than or equal to -ge

test expression or [ expr ] String Comparisons Meaning Operator            string1 is equal to string2 string1 = string2 string1 is NOT equal to string2 string1 != string2 string1 is NOT NULL or not defined  string1 string1 is NOT NULL and does exist -n string1 string1 is NULL and does exist -z string1

test expression or [ expr ] Logical Operators Meaning Operator            Logical NOT ! expression Logical AND expression1  -a  expression2 Logical OR expression1  -o  expression2

if …else…fi If given condition is true then command1 is executed otherwise command2 is executed. Syntax: if condition then command1 else if condition is not true then execute all commands up to fi fi

Exercise ( if..else with parameters) if [ $# -eq 0 ] then echo " Enter one argument “ exit 1 else   echo " The first argument is $1 " fi

if …else…fi $ chmod 755 isnump_n $ ./isnump_n 5 $ vi isnump_n # Script to see whether argument is positive or negative if [ $# -eq 0 ] then echo "$0 : You must give/supply one integers" exit 1 fi if test $1 -ge 0 then echo "$1 number is positive" else echo "$1 number is negative" fi $ chmod 755 isnump_n $ ./isnump_n 5

if …else…fi Syntax: if condition Then then ..... .. do this else ....

Nested if-else-fi $ vi nestedif osch=0 echo "1. Unix (Sun Os)" echo "2. Linux (Red Hat)" echo –n "Select your os choice [1 or 2]? " read osch if [ $osch -eq 1 ] ; then      echo "You Pick up Unix (Sun Os)" else        if [ $osch -eq 2 ] ; then              echo "You Pick up Linux (Red Hat)"        else              echo "error only 1 or 2"        fi fi $ chmod 755 nestedif $ ./ nestedif

Multilevel if-then-else Syntax: if condition then condition is zero (true - 0) execute all commands up to elif statement elif condition1 then condition1 is zero (true - 0) elif condition2 condition2 is zero (true - 0) else None of the above condtion,condtion1,condtion2 are true (i.e. all of the above nonzero or false) execute all commands up to fi fi

$ vi elf # Script to test if..elif...else # if [ $1 -gt 0 ]; then   echo "$1 is positive" elif [ $1 -lt 0 ] then   echo "$1 is negative" elif [ $1 -eq 0 ] then   echo "$1 is zero" else   echo "Opps! $1 is not number, give number" fi $ chmod 755 elf $ ./ elf 8 $ ./ elf -3 $ ./ elf 0 $ ./ elf a

for Loop Syntax: for { variable name } in { list } Do execute one for each item in the list until the list is not finished (And repeat all statement between do and done) done $ vi testfor for NUMBER in 1 2 3 4 5 do echo "Welcome $NUMBER times" done $ vi for2 LIMIT = 10 for ((  i = 1 ;  i <= LIMIT;  i++  )) do   echo "Welcome $i times" done

for Loop $ vi nestedfor for (( i = 1; i <= 5; i++ ))      ### Outer for loop ### do     for (( j = 1 ; j <= 5; j++ )) ### Inner for loop ###     do           echo -n "$i "     done   echo "" #### print the new line ### done

while loop Syntax: i=$1 while test $i != 0 do echo –n "$i ," while [ condition ] do command1 command2 command3 .. .... done Write script to print numbers as 5,4,3,2,1, using while loop. The biggest number is supplied as command line argument. i=$1 while test $i != 0 do echo –n "$i ," i=`expr $i - 1` done echo " "

for (( i=1; i<=5; i++ )) do for (( j=1; j<=i; j++ )) Exercise (1) Write shell script using for loop to print the following patterns . 1 22 333 4444 55555 for (( i=1; i<=5; i++ )) do for (( j=1; j<=i; j++ )) echo -n "$i" done echo ”“