Bash Shell Scripting -headlines-

What is the comment, why and how? How can I make my script receive arguments? How to execute scripts ?

 $ bash script_name 

 $ ./script_name –where pwd=./

What is variable? Is there any Special variables? How and why ?

Notes :

Double (") and single (') quotes behave differently Do not confuse the backtick (`) with single quotes

var1="value"
echo " the value is $value "
echo ' the value is $vale '

they are different.
 

How to skip special chracters ? Using ' ' or using backslash .

 

note : how ` and ' are different this …GRR

Var=`du –s /home/sakia | cut –f 1 `
echo "the sakia using /home/sakia $Var kilobytes"

think about this how can I use environment #variables here
echo " the  $USER using /home/sakia $Var Kilobytes"  

it is a challenge sequence to make the script 
for generic use as it asks u to enter the home 
directory of the desired home dir.
it may notify u if the user is exist on ur machine or not . check the /etc/passwd 

It may be easy if we continuo the session

Intorduaction to IF statement There is 4 operations which is equal "=" ,

not equal "!=" ,

non-zero length "–n"

and zero-length "–z"

Start new script

!/bin/bash
String1="Egypt linux User's Group";
String2="EGLUG";
if "$String1 = $String2 "
then 
   echo "first string equals the next";
else
echo "they are not equal "
fi
if "-n  $String1 "
then 
echo " string is not empty ,which is $String1 ";
else 
echo " string is empty ";
fi

If operation for numerical comparisons "-eg" equal , "-ne" not equal , "-gt" greater than ,"-ge" greater than or equal , "-lt" less than and "le" less or equal .

Start new script

num1=10;
num2=15;
num3=20;
if $num1 –ge $num2
then 
    echo "num1 is greater than num2";
else 
echo " num2 is greater than num1";
fi
let num4=$num1+$num2;
if $num4 –gt $num3
then 
echo  "$num4 is greater than $num3";
else 
echo "$num4 is less than or equal to num3";
fi   

If condition for files and directories. Operation for file comparisons -d the file is directory

-f the file is regular file 3adey ya 3aney

-r is read permission set

-w is write permission set

-x is executable permission set

-s is there any non empty file

dir1=/home/sakia;
file1=/home/sakia/test
if -x $file1
then 
echo "$file is executable ";
else 
echo "$file is not executable ";
fi 
if -d $file1
then 
echo "$file is directory  ";
else 
echo "$file is not directory  "; #it may be link or device .
fi
if -r -$dir1 –a –x $dir1
then 
echo "$dir1 is readable and executable ";
else 
echo "$dir1 is not both readable and executable";
fi