Skip to main content

String Hadling in Bash Shell

Strings can be handled efficiently using string functions in bash shell.
The following are the commonly used functions

Finding length of the string
length: will return the length of the string
Eg:
str=”This is a test string”
len=`expr length “$str”`
echo $len
o/p:21

In bash shell, when you use a dollar sign followed by a variable name, shell expands the variable with its value. This feature of shell is called parameter expansion.
 
Parameter expansion has numerous other forms which allow you to expand a parameter and modify the value or substitute other values in the expansion process. We can use the parameter expansion concept for string manipulation operations.
 
Syntax:${#string}
Eg:
str="This is a test string"
len=${#str}
echo $len

Extracting a substring
substr

Eg: this will extract 3 characters from 2 pos ie; his
str="This is a test string"
sstr=`expr substr "$str" 2 3`
echo $sstr


In the parameter expansion position starts from 0.
Syntax:${string:position:length}
str="This is a test string"
sstr=${str:2:2}
echo $sstr
o/p:his

Deleting substring
Following syntax deletes the shortest match of $substring from front of $string
${string#substring}
Following syntax deletes the shortest match of $substring from back of $string
${string%substring}

Eg:
str="this is test"
echo ${str#*i} # will delete upto i from the begining
echo ${str%e*} # will delete upto e from the end
 
Following syntax deletes the longest match of $substring from front of $string
${string##substring}
Following syntax deletes the longest match of $substring from back of $string
${string%%substring}
Eg:
str="this is test"
echo ${str##*i}
echo ${str%%s*}


Find and replace string

Replace only first match
${string/pattern/replacement}
Eg:
str="this is test"
echo ${str/is/was}
 
Replace all the matches
${string//pattern/replacement}
Eg:
str="this is test"
echo ${str//is/was}
 
Replace in the beginning.Following syntax replaces with the replacement string, only when the pattern matches beginning of the $string.
${string/#pattern/replacement}
Following
syntax replaces with the replacement string, only when the pattern
matches at the end of the given $string.
${string/%pattern/replacement}

Sample Program:
Check the given string is palindrome or not
echo "enter the string...."
read str
len=${#str}
i=1
rstr=""
while [ $i -le $len ]
do
c=`expr substr "$str" $i 1`
rstr=$c$rst r
i=`expr $i + 1`
done
echo "reversed String is ...$rstr"
if [ "$str" = "$rstr" ]
then
echo "Palindrome"
else
echo "Not palindrome"
fi

Labels

Labels:

Comments

Post a Comment

Popular posts from this blog

Writing a Bash Shell Script

Bash shell scripts in Linux are text files that contain a series of commands that can be executed by the Bash shell. Bash (Bourne Again Shell) is a popular shell in Linux and UNIX systems, and shell scripts are used to automate tasks, configure systems, or perform a sequence of operations. How to Write a Bash Shell Script Create a New File: You can create a new script using any text editor like nano , vim , or gedit . gedit myscript.sh Write the Script: A basic shell script begins with a "shebang" ( #!/bin/bash ) to specify the interpreter that will be used to execute the script. The rest of the file contains the commands to be run. Example of a simple script: #!/bin/bash # This is a comment echo "Hello, World!" # Print "Hello, World!" #!/bin/bash : Specifies that the script will be executed using the Bash shell. echo "Hello, World!" : A command that prints the string "Hello, World!" to the terminal. Comments: Any line starting ...
Post a Comment
Read more

Different syntax for writing arithmetic expressions in bash shell

#!/bin/bash echo "Enter two numbers" read a b s=`expr $a + $b` echo "Sum1=$s" s=$[$a+$b] echo "sum2=$s" ((s=$a+$b)) echo "sum3=$s" ((s=a+b)) echo "sum3=$s" let s=$a+$b echo "sum4=$s" let s=a+b echo "sum4=$s" Note:bash shell support only integer arithmetic.zsh support operations on real numbers.We can use bc in bash shell to do real arithmetic. Eg: echo "$a*$b"|bc # where a and b are real Mathematical Operators With Integers Operator Description Example Evaluates To + Addition echo $(( 20 + 5 )) 25 - Subtraction echo $(( 20 - 5 )) 15 / Division echo $(( 20 / 5 )) 4 * Multiplication echo $(( 20 * 5 )) 100  % Modulus echo $(( 20 % 3 )) 2 ++ post-increment (add variable value by 1) x=5 echo $(( x++ )) echo $(( x++ )) 5 6 -- post-decrement (subtract variable value by 1) x=5 echo $(( x-- )) 4 ** Exponentiation x=2 y=3 echo $(( x ** y )) 8
Post a Comment
Read more

Basic Linux Commands For Beginner's

Basic Linux Commands for Beginners Linux is an Operating System’s Kernel. You might have heard of UNIX. Well, Linux is a UNIX clone. But it was actually created by Linus Torvalds from Scratch. Linux is free and open-source, that means that you can simply change anything in Linux and redistribute it in your own name! There are several Linux Distributions, commonly called “distros”. A few of them are: Mint Ubuntu Linux Red Hat Enterprise Linux Debian Fedora Kali Linux is Mainly used in Servers. About 90% of the Internet is powered by Linux Servers. This is because Linux is fast, secure, and free! The main problem of using Windows Servers are their cost. This is solved by using Linux Servers. Forgot to mention, the OS that runs in about 80% of the Smartphones in the World, Android, is also made from the Linux Kernel. Yes, Linux is amazing! A simple example of its security is that most of the viruses in the world run on Windows, but not on Linux...
4 comments
Read more