HPUX - Shell Programming - Branches

Return Codes

The shell variable ? holds the return code of the last command executed

{

$ echo $?

1

$ adf

sh: adf:  not found.

$ echot $?

sh: echot:  not found.

$ echo $?

127

$ false

$ echo $?

1

$ echo $?

}

test command

test command can evaluate the condition of Integers, Strings, Files [조심! 실습파일은 test 말고 test.sh 등으로 작성, sh는 쉘을 의미]

test - Numeric Test

-lt, -le, -gt, -ge, -eq, -ne (less, less or equal, greater, greater or equal, equal, not equal]

{

$ test 10 -gt 5

$ echo $?

0

$ test 10 -lt 5

$ echo $?

1

$ x=10

$ test $x -gt 5

$ echo $?

0

$ [ $x -gt 5 ]      //test command syntax

$ echo $?

0

}

test - String Test

test str1=str2, str1!=str2 

{

$ x=yes

$ [ $x = yes ]

$ echo $?

0

$ [ $x != yes ]

$ echo $?

1

}

test - File Test

test -f filename or dirname, -d filename or dirname  (-f file?, -d directory?, -r readable? -w writable? -x exist and executable?)

test - Other Operator

-o OR, -a AND, ! NOT, \( \) GROUPING

exit - return code of the last command

$ cat exit_test

echo exiting program now

exit 99

$ exit_test

exiting program now

$ echo $?

99

if 

if [ $x -lt 10 ]

then echo String 1

fi

if-else 

if [ $x -lt 10 ]

then echo String 1

else then echo String 2

fi

if [ $x -lt 10 ]

then echo String 1

else 

if [ $x -gt 5 ]

then echo String 2

else echo String 3

fi

fi

elif

if [ $x -lt 10 ]

then echo String 1

elif [ $x -gt 5 ]

then echo String2

else echo String3

fi

case 

case $ANS in

yes)  echo O.K. 

;;                    //break;

no)  echo no go

;;

*) echo keep trying

;;

esac

$ vi menu_with_case

"menu_with_case" [New file]

echo type d date, w who, l ls

read choice

case $choice in

    [dD]*)  date    ;;

    [wW]*)  who     ;;

    l*|L*)  ls      ;;

    *)  echo invalid ;;

esac

exercise

{

$ vi greeting1

echo type [A] or [B,b] or [C,quit]

read ANS

case $ANS in

    A*) echo good morning   ;;

    [Bb]*) echo good after noon ;;

    C*|quit*) exit ;;

    *) echo "error!"

    exit 99 ;;

esac

}

{

$ vi greeting2

time=$(date +%H)

if [ $time -lt 12 ]

    then echo good morning

elif [ $time -ge 12 -a $time -lt 18 ]

    then echo good afternoon

else

    echo good evening

fi

}

{

$ vi m16_9.sh

echo display current directory? [yes or no]

read ANS

if [ "$ANS" = yes ]

    then echo $(pwd) | ls

elif [ "$ANS" = no ]

    then echo what directory would you like to see?

    read ANS

    if [ -d $ANS ]

        then cd $ANS

    else

        echo directory doesn\'t exist

    fi

fi

}