Unix Shell Scripting Tutorial - page 2 | Web Technology Experts Notes

Question: What are special variable in unix?
Special variable are those variable which are reserved by unix shell. For Example $$ is special variable and it return the current process id.

Question: List the special variable?

$$: Give the current process ID.
$0: File name of current script.
$n: $1 will give first argument, $2 will give 2nd argument.
$#: The number of arguments supplied to a script.
$*: Return all the arguments.
$?: The exit status of the last command executed.
$!: Process number of last command

Question: Can we define array variables?
Yes, we can define.

NAME01="Name 1"
NAME02="Name 2"
NAME03="Name 3"
NAME04="Name 4"
NAME05="Name 5"

Question: How to define array variable and use them?
Define Array variable

NAME01="Name 1"
NAME02="Name 2"
NAME03="Name 3"
NAME04="Name 4"
NAME05="Name 5"

Use single variable

echo $NAME[2];

Print each and every variable

for i in NAME01 NAME02 NAME03 NAME04 NAME05
do
  echo $i;
done

Question: How to print array in single line?

echo  ${NAME[*]};

Question: How to use Relational Operators?

-eq: Equal
-ne: Not Equal
-gt: Greater than
-lt: Less than
-ge: Greater than OR Equal to
-le: Less than OR Equal to

Question: How to use Boolean Operators?

!: Not
-o: OR
-a: And

Question: Give an example of while?

a=1
while [ $a -lt 10 ]
do
   echo $a
   if [ $a -eq 5 ]
   then
      break
   fi
   a=`expr $a + 1`
done

Question: What is Substitution?
The shell performs substitution when it encounters an expression that contains one or more special characters.

Question: Give few example of Variable Substitution?
Variable substitution enables the shell programmer to manipulate the value of a variable based on its state.
Examples

${var}

${var:-word}

If var is null, word is substituted for var.

${var:=word}

If var is null, var is set to the value of word.

${var:?message}

If var is null, message is printed to standard error.

${var:+word}

If var is set, word is substituted for var.

Question: What are the Metacharacters?
metacharacters have special meaning while using them in any Shell Script and causes termination of a word unless quoted.

Following are the meta characters.

    
        * ? [ ] ' " \ $ ;  ( ) | ^

Thursday, 24 August 2017

Unix Shell Scripting Tutorial - page 2

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