Bash Split String into Array [5 Robust Methods]

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

 

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:

• Bash Manual
• Advanced Bash Scripting Guide
• Bash Pitfalls (common issues and challenges encountered in Bash scripting)
• man page of tr
• man page of read
• What is IFS in Bash?