How to Use String Functions in Bash? [Examples Included]

You can follow these syntaxes to implement string functions in Bash:

1. Declaring String with “declare” Command: declare a="string value"
2. Asking Input from User with “read” Command: read variable_name
3. Determining Length of String: length="${#string_name}"
4. Extracting Substring from String: extracted_string="${original_string:start:end}"
5. Concatenating Strings in Bash: concatenated_string=${string1}${string2}
6. Splitting Strings Into Arrays in Bash: read -a array_name <<< "$string_name"

Before using, a string variable must be declared properly, and then the string can be assigned to the declared string variable either manually or from user input. There are string functions in Bash for determining the length of a string, concatenating multiple strings into a single string, and splitting strings into arrays and individual words according to the specified Internal Field Separator(IFS). In this article, I will briefly discuss these.

1. Declaring String with “declare” Command

The declare command declares a variable. The syntax for declaring a variable and assigning a value to that variable is: declare option variable_name=value. Here is a bash script for this:

#!/bin/bash

declare -r a="Linuxsimply"
echo "$a"

2. Asking Input from User with “read” Command

A value can be assigned to a variable by taking input from the user with the read command. The read command reads input from the user using the syntax: read variable_name. Here is a bash script:

#!/bin/bash

read -p 'Enter your name: ' a
echo "Hello $a"

3. Determining Length of String

The string contains various types of characters. To determine a string’s length, put ‘#’ before the string variable name. The syntax is length="${#variable_name}". It will return the length of the string contained in variable_name. Here is a bash script:

#!/bin/bash

a="Linuxsimply"
l="${#a}"
echo $l

4. Extracting Substring from String

Parameter expansion can extract a specific substring from a string. Use the syntax substring="${string:start:end}" to extract a substring from the original string. Here is the bash script to do so:

#!/bin/bash

a="LinuxSimply"
b=”${a::5}”
echo $b

5. Removing Matched Substring from Original String

Parameter expansion can remove substring from a string. To remove a dot and a substring from the end of a string, use the syntax: new_string="${original_string%.*}". Here is a complete bash script:

#!/bin/bash

declare -r a="linux.simply.sh"
echo "original string: $a"
b="${a%.*}"
echo "manipulated string: $b"

6. Concatenating Strings In Bash

In Bash, concatenation means listing strings one after another. To do so, follow the syntax: concatenated_string=${string_1} ${string_2}. Here is the complete bash script:

#!/bin/bash

a=Linux
b=Simply
var=${a}${b}
echo $var

7. Splitting String Based on Space

The string contains several words separated by space. Set space as the Internal Field Separator(IFS) to split a string based on space. Here is the complete bash script:

#!/bin/bash

a="Welcome to Linuxsimply"
IFS=' '
read -a b <<< "$a"
echo "There are ${#b[*]} words in the text."
for c in "${b[@]}";
do
  printf "$c\n"
done

8. Splitting Strings Into Arrays in Bash

The string stores words separated by space. To split a string into an array in Bash, use the syntax: read -a array_name <<< "$string_name". Here, it will read string, then split it into fields and store them in an array. Below is a complete bash script:

#!/bin/bash

a='Linux Simply'
read -a b <<< "$a"
for c in "${b[@]}";
do
  printf "$c\n"
done

9. Returning a String from Bash Functions Using Global Variable

A global variable is a variable that exists inside and outside of a function. A bash function can print a string using a global variable. This output can be captured after calling the function; the global variable value will be according to the function definition. Here is a complete bash script:

#!/bin/bash

function FF()
{
  returnval='Linux Simply'
}
returnval='SOFTEKO'
echo "Before: $returnval"
FF
echo "After: $returnval"

10. Returning a String from Bash Functions Using Local Variable

Inside a function, a local variable can be defined with a value, and the variable’s value can be captured using command substitution. Here is an example of returning a string from bash functions using a local variable:

#!/bin/bash

function FF2()
{
  local  returnval='Hello from LinuxSimply'
  echo "$returnval"
}
val=$(FF2)
echo $val

Conclusion

In conclusion, string manipulation allows users to update and edit strings according to necessity. There are many types of string functions that are discussed in this article. It will guide the learner in implementing these functions to achieve the intended task.

People Also Ask

Can Bash functions return strings?

Bash functions can not return strings directly. At first, use the echo command to print a string and capture the output when the function is called.

What is the position of a string in Bash?

The bash strings are zero-indexed. The position of the first character is ‘0’, that of the second character is ‘1’, and so on.

How to connect strings in Bash?

To connect or concatenate multiple strings into a string, place them one after another. If a="Good " b="Morning" then greeting="$a$b" concatenates the strings a and b and keeps them to the variable greeting.

How to split a string based on string Bash?

To split a string into an array in Bash, use the syntax: read -a array_name <<< "$string_name". It will split the words inside the string, and the -a option will enable it to store the words inside the array_name array.

How to find and replace string Bash?

To find and replace a string in bash, use the syntax: echo 'Original String' | sed 's/old_word/new_word'. Here, the original string will be piped to the sed command, where the ‘s’ option stands for substituting the old_word with the new_word.

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