Shell Scripting 25 Basic Important Syntax Tips Tricks

1)How To Check RPM is installed or Not in Shell Script.
CHECK="tftp nfs http"
for i in $CHECK ; do
RPMFILE=`rpm -qa $i`
echo $RPMFILE;
done

2)/etc/init.d/fucntion it has some default predefined function. like
success,failure we can use these function from there itself.


3)Shell Scripting File Proprieties.
-f
File
-d
Directory
-r
File name test for readable
-w
File name test for writable
-x
File name test for executable or not
-s
File is not empty


4)Declare the function and call the function.
Function_name()
{
statement ;
}
To call the function
function_name

5)Write the Data into the File.
#cat > File_name << EOF
data1
data2
EOF

6)How to Debug the Shell Scripting
#bash -x ./script.sh [ debugging the script file] Display all the command and arguments when they are executed.
#bash -v ./script.sh [ verbose mode ]
#bash -xv ./script.sh


7)Shell Scripting Logical And OR NOT
!
Logical Not
-a
Logical And &&
-o
Logical Or ||

! tests for logical not, -a tests for logical and, and -o tests for logical or.

8)Sed Important Option.
-i
Insert
#sed -i '5i/JESUS' sed-test.txt Insert Word in 5th Line.
-d
Delete
#sed 5d -i File-Name
-e
Expression
-s
Search
-g
Global
-n 10p
Print 10th Line
-n "2~3p” 2nd line, 5th line,8th line.
-w
Word
-n


9)Linux System Call Process
fork()
To Create New Process
exec()
Execute New Program In Process
wait()
Wait Until created process is completed.
exit()
Exit Process Execution.
getpid()
Get the Process ID of Current Process.
getppid()
Get Parent Process Identifier.
nice()
Existing Priority of process.
brk()
Increase / Decrease Data Segment Size of process.

10)Shell Script Passing Argument Argument
$#
Count Total No of Passed Argument.
$0
Script Name[./script $0 $1] here script is $0
$1
Argument
$$
Process ID of Current Executing Process.
$!
Which process recent went to background
$?
Give the status of last executed Command.
$@ $*
Display all the command Line Argument.

11)Comparison Operation.
-lt
Less Than
-gt
Greater Than
-eq
Equal
-ne
Not Equal
-ge
Greater Than Equal
-le
Less Than Equal



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