Thursday 24 August 2017

Unix Shell Scripting Tutorial - page 2

Unix Shell Scripting Tutorial - page 2

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?
  1. $$: Give the current process ID.
  2. $0: File name of current script.
  3. $n: $1 will give first argument, $2 will give 2nd argument.
  4. $#: The number of arguments supplied to a script.
  5. $*: Return all the arguments.
  6. $?: The exit status of the last command executed.
  7. $!: 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
  echo $i;

Question: How to print array in single line?
echo  ${NAME[*]};

Question: How to use Relational Operators?
  1. -eq: Equal
  2. -ne: Not Equal
  3. -gt: Greater than
  4. -lt: Less than
  5. -ge: Greater than OR Equal to
  6. -le: Less than OR Equal to

Question: How to use Boolean Operators?
  1. !: Not
  2. -o: OR
  3. -a: And

Question: Give an example of while?
while [ $a -lt 10 ]
   echo $a
   if [ $a -eq 5 ]
   a=`expr $a + 1`

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.

If var is null, word is substituted for var.
If var is null, var is set to the value of word.
If var is null, message is printed to standard error.
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.
        * ? [ ] ' " \ $ ;  ( ) | ^