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What are things needed in a programming Language for basic stuff ?

1. Variables and Data types
2. Control Statements [ if, while, for ..]
3. Arithmetic Expressions and Boolean Expressions

1. Arrays
2. Regular Expressions and related tools
3. I/O Functions for interacting with the user and the environment
4. Functions
5. Others

Start Note

shell programs are saved with .sh extension. They can be run with

#shellname program.sh
#Example
sh pro1.sh

There are many shells such as Z shell, C shell , bash, an lot of others. Most common is bash. Install any if you don’t have any. Ask your
administrator for permission if you don’t have sufficient rights for
executing programs.

This article assumes that you are using bash and you have programming experience.

Variables and Data types

Variables in shell can be set by simply typing

VARIABLE=VALUE

Examples are

numberVariable=3;
realVariable=3.14;
stringVariable_1=pi;
stringVariable_2="pi";

Control Statements [ if, while, for ..]

If statement

if[testCondition]
then
     #codeblock
fiORif[testCondition]
then
    #code block
else
   #codeblock
fi

Examples

if [ $a -eq $b ] # -eq tests whether left operand is equal to the right operand
then
   echo "a is equal to b"
else
   echo "a and b are not equal"
fi

While Statement
Like other programming Languages, syntax of while is shell is similar

while [ testCondition ]
do
    #code block
done

Examples

i=0
while [ $i -lt 10 ]
do
  echo $i;
  i=$((i+1));   #increment the varaible i
done

For statement
for statement syntax is

for variable in sequence
do
  #codeblock
done

variable is a usual variable whereas sequnce is a list of values separated by spaces.
Example

for i in 1 2 3 4 5 6
do
    echo $i;
done

Arithmetic Expressions

Usual Arithmetic expressions are possible in shell which includes operators +, -, *, / and % and usual hard-cored values and variables (prefixed with $). You should enclose the arithmetic expressions in $((exp)) or any other standard formats. See the code snippet below…

i=5;
echo $((1+2));
echo $(($i-3));
echo $((7/2));
echo $((7%5));

Boolean Expressions

This is the area where shell differs from most of the languages. Boolean expression is of of the form operand -relop operand
operand can be hard-core values or variables or themselves boolean expressions and relop can be one of the following:
• -lt for less than operator ( “<” in other languages )
• -le for less than or equal to operator ( “≤” in other languages )
• -gt for greater than operator ( “>” in other languages )
• -ge for greater than or equal to operator ( “≥” in other languages )
• -eq for equal to operator ( “=” in other languages )
• -ne for equal to operator ( “!=” in other languages )
• -a for logical and operator ( “&&” in other languages )
• -o for logical or operator ( “||” in other languages )
• ! expression— for not operator ( “! expression “ in other languages)
Look at the example below

if [ 3 -eq 3 -a 3 -ge 2 ]
then
    echo "work begins";
fi

if [ ! 3 -ge 4 ]
then 
    echo "! 3>4";
fi

That’s it for now. We can just take a moment and try to use it in a
scenario. Next Part is my favourite. I always use that snippet for
organizing Downloads Directory.
Sample Program
Lets us consider a simple scenario. Consider that you have all videos of every season of your favourite TV series in a single Folder and you want to organize them into seasons. Thanks to appropriate Naming (S0xE0x ) of episodes. Following snippet will do the job for you.

for i in `seq 5` #consider that we have 5 seasons 
do
    mkdir S$i;  # creating directory
    mv *S$i* S$i;  #moving the files
done

f this 4 line script can save that much work, Just think about what else you can do with it.

End Note

So if you find yourselves typing some commands or tasks repeatedly, try to make it as a shell program.
Congratulations! You made it to the end. I hope you found this article useful.
Check out my profile to find more articles.
Thank You.
Happy Coding with Shell ………