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
do
  echo $i;
done

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?

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.

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

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Unix Shell Scripting Tutorial - page 1

Question: How to create file shell script file?

echo "Hello World? How are you all?";

Question: How to make a file executable?

chmod a+rx script1.sh

Question: How to run execute file?
Just with name, you can execute.

script1.sh

Question: How to add comment in shell script files?
Use hash(#) before the line for comment.

chmod a+rx script1.sh

Question: How to use variable in shell script file?

name="Manoj"
echo "My Name is : $name"

Question: What is variable convention?
The name of a variable can contain only letters (a to z or A to Z), numbers ( 0 to 9) or the underscore character ( _).


Question: How to define read only variable?

readonly version="10.2"
echo "Version is : $version"

Question: How to unset variable?

name="Manoj"
unset name;

Question: What are different type of variable?

1. Local Variables: A local variable is a variable that is present within the current instance of the shell.
2. Environment Variables: An environment variable is available to any child process of the shell. Some programs need environment variables in order to function correctly.
3. Shell Variables: A shell variable is a special variable that is set by the shell.

Question: How to use Escape Characters?
Use slash \ for Escape the character;

echo "Hello \"User\""; // Hello "User"
echo "Slash \\" ;// Slash \

Question: How to use expression in shell script file?
Use expr enclosed with caret (~), For Example

myvar=10;
result=`expr 10 * 5`
echo "Multiple: $result";

myvar=10;
result=`expr 10 + 5`
echo "Additon: $result";

myvar=10;
result=`expr 10 -5`
echo "Subtract: $result";

Question: How to use loop?

for i in 1 2 3 4 5
do
  echo "Number $i"
done

Question: How to use if else condition?

if [ 2 = 3 ]
then
  echo "Both are equal"
else
  echo "Both are not equal"
fi

Question: How to use if else elseif condition?

if [ 2 = 3 ]
then
  echo "Both are equal"
elseif [ 2 > 3 ]
  echo "2 is greater than 3"
  else
  echo "2 is less than 3"
fi

Question: How to read from user?

echo "What is your name?"
read name
echo "Your name is $name"

Question: How to search a folder with name?

find ~ -type d -name "*foldername*" -print

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