Bash Split String into Array [5 Robust Methods]


Deepak Prasad

Shell Scripting

Introduction - Bash split String into Array

In Bash scripting, working with strings is very common. One important skill is learning how to take a string and split it into an array. Many people search for this using phrases like "bash split string into array" or "bash convert string to array." Knowing how to do this is a key part of Bash scripting. It helps in making scripts that can work with texts in a flexible way.

In this guide, we will learn different ways to turn a bash string into an array. We are going to look at several methods like using the Internal Field Separator (IFS), the ‘read’ command, loops, regular expressions, and pattern matching.

First, we will use the IFS to decide where we should split the string. We will also use the ‘read’ command, a simple way to break up strings. Another way is using loops, which lets us go through a string and split it step by step. If you are looking for more advanced ways, we will also talk about using regular expressions and pattern matching to split strings in more complex ways.

By the end of this guide, you will know how to "bash split string into array" and "bash convert string to array," making your bash scripts better and more powerful. Let’s start learning!

 

1. Using IFS (Internal Field Separator)

The IFS (Internal Field Separator) is a powerful tool when you want to "bash split string into array." The IFS defines a character or characters used as a delimiter for splitting a string into an array. When we set the IFS variable and read the string, the bash automatically splits the string based on the IFS value and reads it into an array.

#!/bin/bash

# Define a string
string="apple banana orange"

# Set the IFS (Internal Field Separator) to space
IFS=' '

# Use read to bash convert string to array
read -ra myvar <<< "$string"

# Output the array and its length
echo "My array: ${myvar[@]}"
echo "Number of elements in the array: ${#myvar[@]}"

The IFS (Internal Field Separator) is a system variable that determines how Bash recognizes word boundaries. It's a powerful tool that you can customize using different delimiters to bash split string into array.

Limitations:

  • Changing the IFS value affects other parts of the script, which might lead to unexpected behaviors.
  • Primarily works with single-character delimiters; handling multi-character delimiters might require additional processing.
  • Might require additional configurations or syntax for more complicated strings or patterns.

Let’s explore how to use IFS with various delimiters, such as commas, semicolons, and custom characters.

1.1 Using IFS with Comma as a Delimiter

Setting the IFS to a comma tells Bash to use the comma as the delimiter to split the string into array elements.

#!/bin/bash

# Define a string separated by commas
string="apple,banana,orange"

# Set the IFS to comma
IFS=','

# Use read to bash split string into array
read -ra myvar <<< "$string"

# Output the array and its length
echo "My array: ${myvar[@]}"
echo "Number of elements in the array: ${#myvar[@]}"

1.2 Using IFS with Semicolon as a Delimiter

By setting the IFS to a semicolon, it becomes the character separating the words or tokens in the string.

#!/bin/bash

# Define a string separated by semicolons
string="apple;banana;orange"

# Set the IFS to semicolon
IFS=';'

# Use read to split the string into an array
read -ra myvar <<< "$string"

# Output the array and its length
echo "My array: ${myvar[@]}"
echo "Number of elements in the array: ${#myvar[@]}"

1.3 Using IFS with Custom Character as a Delimiter

You can set the IFS to any custom character, like a pipe |, to be the delimiter, allowing for diverse string splitting scenarios.

#!/bin/bash

# Define a string separated by pipes
string="apple|banana|orange"

# Set the IFS to pipe
IFS='|'

# Use read to split the string into an array
read -ra myvar <<< "$string"

# Output the array and its length
echo "My array: ${myvar[@]}"
echo "Number of elements in the array: ${#myvar[@]}"

 

2. Using the ‘read’ Command

The read command is another intuitive method to bash convert string to array. With read, we can get the user input or read a string, and directly assign the words into an array. It’s like telling bash to read a line of text and save each word in an array.

#!/bin/bash

# Define a string
string="apple banana orange"

# Use read to bash split string into array
read -ra myvar <<< "$string"

# Output the array and its length
echo "My array: ${myvar[@]}"
echo "Number of elements in the array: ${#myvar[@]}"

Limitations:

  • It primarily uses whitespace as a delimiter. Custom delimiters can be used but might require additional configurations or syntax.
  • Handling multi-line strings might require additional loops or processing to accurately split the string into an array.
  • Special characters within the string might affect the splitting process and might need special handling or escaping.

 

3. Using Loops

Using loops for bash string to array conversion is a more manual yet flexible method. With a loop, we can iterate through each character or word in a string and decide how to split it. This method allows us to have more control over how we want to bash split string into array.

#!/bin/bash

# Define a string
string="apple banana orange"

# Initialize an empty array
myvar=()

# Use loop to bash convert string to array
for word in $string; do
    myvar+=("$word")
done

# Output the array and its length
echo "My array: ${myvar[@]}"
echo "Number of elements in the array: ${#myvar[@]}"

Limitations:

  • Implementing loops can make the script longer and more complex, affecting readability and maintainability.
  • Loops, especially nested loops, can impact the performance and efficiency of the script, making it slower for large strings or arrays.
  • Requires more elaborate logic and conditions, making it more prone to errors or unexpected behaviors for various inputs.

 

4. Using Parenthesis

You can split a string into an array using parenthesis () in bash by simply defining the elements within the parenthesis and separating them using spaces. This method is straightforward but is static in nature as you manually define the elements. Here’s how you can do it:

#!/bin/bash

# Defining a string
string="apple banana orange"

# Splitting the string into an array
myvar=($string)

# Output the array and its length
echo "My array: ${myvar[@]}"
echo "Number of elements in the array: ${#myvar[@]}"

In this example myvar=($string): The string is split into words based on spaces, and each word becomes an element of the array myvar.

Limitations:

  • Automatically assumes spaces as delimiters, and custom delimiters are not straightforward to implement.
  • Suitable for simple and consistently formatted strings but might not be effective for more complex or dynamic strings.
  • There is no direct way to specify where the string should split, making it less flexible for custom requirements.

 

5. Using tr (translate or delete characters)

You can use tr (translate or delete characters) command in conjunction with parentheses for splitting strings into arrays. Here’s an example of using tr to replace spaces with another delimiter:

#!/bin/bash

# Defining a string where words are enclosed in quotes
string='"apple pie" "banana split" "orange juice"'

# Replacing spaces outside of quotes with a comma, then removing quotes
string=$(echo $string | tr ' ' ',' | tr -d '"')

# Splitting the string into an array using the comma as a delimiter
IFS=',' read -ra myvar <<< "$string"

# Output the array and its length
echo "My array: ${myvar[@]}"
echo "Number of elements in the array: ${#myvar[@]}"

Limitations:

  • tr cannot directly handle the quotes around words, so additional steps or commands might be needed to manage them.
  • tr operates character-wise and does not understand context like "inside quotes" or "outside quotes."
  • tr primarily works with single-character translations or deletions, making it less flexible for multi-character delimiters or complex patterns.

 

Splitting Multi-Line Strings into Array

Handling multi-line strings is another significant aspect when you’re aiming to "bash split string into array." Multi-line strings are those that span across several lines, and handling them involves breaking the string at each newline character. Below is how you can handle multi-line strings and convert them into an array.

By adjusting the IFS (Internal Field Separator) to a newline character, Bash will recognize each line as a separate element, thus achieving the "bash string to array" conversion. This way, each line of the multi-line string becomes an element in the array.

#!/bin/bash

# Define a multi-line string
string="apple
banana
orange"

# Set the IFS to newline
IFS=$'\n'

# Use read to bash convert string to array within a loop
while read -r line; do
    myvar+=("$line")
done <<< "$string"

# Output the array and its length
echo "My array: ${myvar[@]}"
echo "Number of elements in the array: ${#myvar[@]}"

 

Splitting Strings Based on Multiple Delimiters (Advanced)

Splitting strings based on multiple delimiters is a useful technique when the data is inconsistently separated. Utilizing the IFS with multiple characters allows for a more flexible "bash string to array" conversion.

1. Using Loops with Regular Expressions

Combining loops with regular expressions offers a powerful approach to dissect strings meticulously. It allows for precise "bash convert string to array" operations by iterating through matches.

#!/bin/bash

# Define a string
string="apple,banana;orange|grape"

# Set the IFS to multiple delimiters
IFS=',;|'

# Use read to bash split string into array
read -ra myvar <<< "$string"

# Output the array and its length
echo "My array: ${myvar[@]}"
echo "Number of elements in the array: ${#myvar[@]}"

2. Using Loops with Regular Expressions

Combining loops with regular expressions offers a powerful approach to dissect strings meticulously. It allows for precise "bash convert string to array" operations by iterating through matches.

#!/bin/bash

# Define a string with mixed content
string="apple123 banana456 orange789"

# Use a loop with regex to "bash split string into array"
while [[ $string =~ ([a-zA-Z]+)([0-9]+) ]]; do
    myvar+=("${BASH_REMATCH[1]}")        # Adding matched word to the array
    string=${string#*${BASH_REMATCH[1]}} # Removing the matched part from the beginning of the string
done

# Output the array and its length
echo "My array: ${myvar[@]}"
echo "Number of elements in the array: ${#myvar[@]}"
  • The regex ([a-zA-Z]+)([0-9]+) looks for sequences of letters followed by sequences of numbers within the string.
  • If a match is found in the string, the alphabetical part captured by the regex ([a-zA-Z]+) is added to the array myvar.
  • After a match, this line removes the matched portion (both letters and numbers) from the beginning of the string, preparing it for the next iteration to find further matches.

 

Frequently Asked Questions

How do I split a string by a specific delimiter in Bash?

To split a string by a specific delimiter, you can use the IFS (Internal Field Separator) variable to specify the delimiter and then use the read command to split the string into an array. For example, IFS=',' read -ra my_array <<< "$my_string" will split my_string at each comma.

Can I split a string into an array without using the IFS (Internal Field Separator)?

Yes, you can split a string into an array without explicitly using IFS. One method is using parenthesis (). For instance, my_array=($my_string) will split my_string into an array my_array, using whitespace as a delimiter.

How can I split a string into an array based on multiple delimiters or patterns?

For splitting strings based on multiple delimiters, using a combination of parameter expansion and regular expressions is a viable approach. You can first replace one delimiter with another, and then proceed to split the string.

What is the role of the IFS (Internal Field Separator) in splitting strings in Bash?

The IFS is a special shell variable used to determine how Bash recognizes word boundaries. It's extensively used to control the behavior of the read command, for loops, and other constructs in parsing and processing strings and command outputs.

How can I preserve whitespaces within elements when splitting a string into an array?

To preserve whitespaces within elements, you could enclose each element within quotes or use a unique delimiter. While using IFS and read, elements enclosed in quotes will be treated as single elements.

Is it possible to split a multi-line string into an array, treating each line as an element?

Yes, a multi-line string can be split into an array by setting IFS to a newline character and using the read command within a loop or using array assignment.

How do loops enhance the flexibility and control when splitting strings into arrays?

Loops offer more control in manipulating each element while splitting strings. Using loops, additional operations like trimming, pattern matching, or conditional checking can be performed on each piece of the string as it's split into an array.

Can regular expressions be used for more advanced splitting of strings into arrays?

Yes, Bash supports regular expressions, allowing for more advanced string splitting scenarios. You can use regex patterns in conditions within loops, or in combination with IFS and read, to control how the string is split into an array.

Are there differences in splitting strings into arrays in various shell environments like Bash, Zsh, or Dash?

Yes, there are nuances in syntax and feature support among different shells. Bash, being a comprehensive shell, supports arrays and various string manipulation operations, while some other shells might have limited support or different syntax for similar operations. Always ensure your script is compatible with the intended shell environment.

 

Summary

In summary, splitting strings into arrays is a fundamental task in Bash scripting, offering a pathway to manage and manipulate textual data efficiently. Throughout our discussion, various methods such as using IFS (Internal Field Separator), loops, read command, and advanced techniques involving regular expressions and pattern matching have been explored. Each method comes with its own set of advantages and constraints, emphasizing the need for a thoughtful selection based on the specific requirements of the task, such as delimiter type, string complexity, and the necessity to preserve whitespace within elements.

Key takeaways include the versatility of the IFS and read commands, the power of loops and regular expressions for intricate string manipulations, and the essential considerations for handling special characters and multi-line strings. It is also crucial to be mindful of the distinct characteristics and capabilities of different shell environments like Bash, Zsh, or Dash to ensure compatibility and desired outcomes in string splitting tasks.

For further in-depth study and exploration of these topics, you may refer to the official GNU Bash documentation:

 

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Deepak Prasad

He is the founder of GoLinuxCloud and brings over a decade of expertise in Linux, Python, Go, Laravel, DevOps, Kubernetes, Git, Shell scripting, OpenShift, AWS, Networking, and Security. With extensive experience, he excels in various domains, from development to DevOps, Networking, and Security, ensuring robust and efficient solutions for diverse projects. You can reach out to him on his LinkedIn profile or join on Facebook page.

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5 thoughts on “Bash Split String into Array [5 Robust Methods]”

  1. Thanks for the great insights. Only one thing I noticed for change, in the for loop, I hope it should be i<${#myarray[@]},
    instead of i<=${#myarray[@]}
    as the index starts from zero.

    for (( i=0; i<${#myarray[@]}; i++ )); do
         echo "${myarray[$i]}"
    done
    Reply
  2. I found Method 3 did not work for me… Here is the slightly modifed script:

    #!/bin/bash
    echo `/bin/bash --version`
    echo
    
    myvar="string1,string2,string3"
    
    # Here comma is our delimiter value
    IFS="," read -a myarray <<< $myvar
    
    echo "My array: ${myarray[@]}"
    echo "My array [0]:" ${myarray[0]}
    echo "Number of elements in the array: ${#myarray[@]}"

    (Modified to show the bash version in use and the contents of the first array entry…)

    Here is what I get:

    bash-3.2$ split-string.sh 
    split-string.sh 
    GNU bash, version 3.2.25(1)-release (x86_64-redhat-linux-gnu) Copyright (C) 2005 Free Software Foundation, Inc.
    
    My array: string1 string2 string3
    My array [0]: string1 string2 string3
    Number of elements in the array: 1
    bash-3.2$ 

    It is possibly because my bash version is prehistoric, but I remain surprised that I get no error messages. Interesting the commas have gone when it lists My array[0] despite IFS initialisation…

    Reply

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