How to Find Length of String in Bash [6 Methods]

The length of a string refers to finding the number of characters in a string. It is essential to find length for text processing, input validation, and parse text. The basic syntax to find the length of a string is the ${#string}. The syntax is straightforward and does not require any external command to find the length.

Let’s take a look at different methods to find the length of a string.

6 Ways to Find the Length of a String

Besides the basic syntax hash(#)with curly brackets, there are some other commands like the wc command, awk command, and expr command used to find the length of a string. In this part, I will show 6 methods to find the length of a string in bash.

1. Using Parameter Expansion With “#”

Parameter expansion refers to the process of manipulating and expanding the values of the variable. Using this # symbol with the parameter expansion, you can get the length of the given variable’s value. Generally, the hash(#) symbol is used for commenting, but it is also used as a variable substitution and special parameter in bash.

To know the length of a string, go through the following code:

#!/bin/bash

String="Hello, World!"
length=${#String}

echo "The length of the string is: $length"
EXPLANATION

The string has been declared in a variable string. Then the length of the string is stored in the length variable. The#in the${#String}calculates the length of the following string variable.

Count the length of a string in bash

From the output, you can see the length is counted using the parameter expansion. Rename the file name length.sh according to your preference.

Note: The {#$string} syntax, expr command, while loop counts the leading white space of the first line of a text as a character but the wc and awk commands do not count these spaces as characters.

A. Using Loop to Find the Length of a String

To find the length of a large string use the loop with the {#string} syntax for its efficient and simple structure. Here’s how:

#!/bin/bash

string='Hello, Bash!'
length=0

# Iterate through each character in the string
for (( i=0; i<${#string}; i++ )); do
length=$((length + 1))
done

echo "The length of the string is $length"
EXPLANATION

The for loop iterates over each character in a line. The loop is initialized with i=0 and continues as long as “i” is less than the length of the string(${#string}). It will increment theiwith each iteration.

Using loop to find the string length in bash

B. Using Function to Find the Length of String in Bash

To count the length frequently in the bash script, explore the following code:

#!/bin/bash

function string_length {
string=$1
echo ${#string}
}

string_length 'Hello, World!'
EXPLANATION

Thefunction string_lengthline declared a function whose name is the string length. The argument in the function has been accessed using the position variable$1and storing the input in the string variable The{#string}prints the length of the string.

Find the length using function

Using this function, one can find different string lengths by replacing the input argument.

2. Using “wc” Command

The wc command is the command line utility which stands for word count. You can use the command to count the number of lines, words, and characters.

To find the length of a string using thewccommand, follow the below script:

#!/bin/bash 

string="Hello, Bash!" 
length=$(echo -n $string | wc -m) 

echo "The length of the string is $length"
EXPLANATION

The string is declared in a string variable with a double quote. The-noption with the echo command prints the string without a newline character. The output of theechocommand has been piped to thewccommand using the pipe(|) operator. The wc command with the-moption counts the character of the output of theechocommand.

find the length using wc command

3. Using “expr” Command

The expr command is the command line utility that evaluates the expression following this command. The basic syntax of the expr command isexpr EXPRESSION. Replace the expression according to user preference.

To find the length of a string use the length operator with theexprcommand. Here is how:

#!/bin/bash

my_string="Hello, World!"
length=$(expr length "$my_string")

echo $length
EXPLANATION

The$(expr length "$my_string")returns the length of the my_string. The length “$my_string” is the expression in theexprcommand.

Count the characters using expr command

 Note: To find the length of a string you can use the expr command with the: '.*'. Here is how:

#!/bin/bash

string="Hello, World!"
length=$(expr "$string" : '.*')

echo "The length of the string is: $length"

The comparison operator:count the common characters between the previous and latter variable of “:”. The.* matches the entire string. The “.*” can be replaced by the string itself. However, the regular expression may not be portable with different versions of theexprcommand.

4. Using the “awk” Command

The awk command is the command line utility for text processing and pattern matching. The basic syntax of the awk command isawk 'pattern { action }' input_file. Here the pattern indicates the conditions or regular expression and the action to be performed when the pattern matches. If the pattern is missing then the action will be performed on the whole string. The input_file can be piped with the echo command.

To find the length of the string, use theawkcommand with the length operator. Here is how:

#!/bin/bash

 my_string="This is a sample string" 
echo $my_string | awk '{print length}'
EXPLANATION

The output of theecho $my_stringcommand is piped to theawkcommand. Here the print length is the action that will be performed on the string. The awk command calculates the length using the built-inlengthoperator and prints the output to the terminal.

Count the characters using awk command

5. Using “perl” to Find the Length of String

To find the length of a string, use theperlcommand with the pipe operator. Here’s how it looks like:

#!/bin/bash

string="It is the new string. The length of the string should be counted."
echo "$string" | perl -nle "print length"
EXPLANATION

The pipe operator takes the output from theechocommand and uses it as the input for theperl command.  The-noption loops around every line of input. But in this case, it calculates the length of entire the string. The-loption is used to add a newline character to each print statement automatically. The-eoption allows execution of the script.

Count the characters using perl command

From the image, you can see the number of characters is about 65.

6. Using the While loop

The while loop with the read command allows to read input, iterate through data, and perform operations. But in this case, it simply reads the string character by character and counts the length.

To find the length using the while loop, follow this script:

#!/bin/bash

string="This is a new string"
n=0

while read -n1 character; do
n=$((n+1));
done <<(echo -n "$string")

echo "Length of the string is $n "
EXPLANATION

Thenvariable is initialized with a value of 0 and the variable counts the characters in the string. Thereadcommand reads each character from the input and stores it into character. Inside the loop, the variable n is increased by 1 in each iteration. In thedone <<(echo -n "$string"), the output of theechocommand which is the string, is redirected as input into the while loop. The-n option is used to print characters without newline characters.

Using loop find the length of the string

Here in the image, you can see the length of the string which is 20. Rename the script according to your preference.

Find the Length of String Without White Space in Bash

The white space refers to the blank characters that represent the vertical or horizontal space in the text. If a line contains white space, the spaces are considered a character and counted as a string length.

To find the length of a string without counting the space, explore the following code:

#!/bin/bash

originalString="Hello, this is a string with spaces."

# Remove whitespaces from the string
stringWithoutSpaces=$(echo "$originalString" | tr -d ' ')

# Calculate the length of the string without whitespaces
lengthWithoutSpaces=${#stringWithoutSpaces}

echo "Original string: $originalString"
echo "String without spaces: $stringWithoutSpaces"
echo "Length of the string without spaces: $lengthWithoutSpaces"
EXPLANATION

The original string is piped to the tr command in echo “$originalString” | tr. The tr command is used to delete the white space in the string. With the -d option the tr command deletes the (‘ ‘) space. Then the {#string} is used to count the length of the string.

Without space count the length

Conclusion

The article shows a few methods by which the user can easily learn how to find the length for efficient text processing in bash scripting. Among these methods, the parameter expansion is the simplest and easiest method to calculate the length, for large strings, use the for loop with the parameter expansion to find the length.

People Also Ask

How to verify the length of a string?

Verifying a string length refers to the process of checking if a string fulfills a minimum length. It is important to verify the length of a string for handling data and prevent invalid results.

To verify the length, explore the following code:

#!/bin/bash

str="Hello, World!"
[ $(echo -n "$str" | wc -c) -gt 6 ] && echo 'valid' || echo 'invalid'

Here, The output of theechocommand has been piped to thewccommand as input. The test conditional[...-gt 6]is used to check if the value obtained in the$(echo -n "$str" | wc -c)is greater than 6. If the result of the[$(echo -n "$str" | wc -c) -gt 6 ]command is true then the logical AND && operator will be executed. If it returns false then it will execute the logical OR || operator.

How to check string length 0 in Bash?

To check if a string length is 0 or an empty string, use the-zconditional which returns true if the string length is 0 and returns false if the string length is not equal to 0. You can also use the== operator when comparing with an empty string to check if the string length is 0. Here how it looks like:

#!/bin/bash

string=""

if [ -z "$string" ]; then
echo "String is empty."
else
echo "String is not empty."
fi

To check if a string is empty or not, use the-zoption. If it is empty then it returns the true value and if the string is not empty it will return false.

How to compare string length in bash?

To compare the length of two strings whether it is equal or not, use the following code:

#!/bin/bash

if [[ ${#string} == ${#string_two} ]]; then 
echo "Strings are equal by length." 
else 
echo "Strings are not equal by length." 
fi

You can use the double bracket ([[ ]]) for the conditional operation. And use the double equal sign for equality comparison within the double bracket. In the double bracket if the condition is true then it prints the block in the if statement otherwise it prints the block of the else statement.

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Afia Zahin Oishi

Assalamualaikum, I am Afia Zahin, completed my graduation in Biomedical Engineering from Bangladesh University of Engineering and Technology, currently working as a Linux Content Developer Executive at SOFTEKO. A high achieving professional with a strong work ethic and able to work in a team in order to consistently achieve my goal and build my skillset. Able to handle difficult problems with patience and swift decision-making. Read Full Bio

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