How to Replace a Substring in a String in a Shell Script

To replace a substring in a string in a shell script, you can use various built-in string manipulation functions and techniques available in Linux bash. In this answer, I will provide two possible approaches to accomplish this task.

Approach 1: Using the sed Command

The sed command is a useful tool for stream editing in Linux. It can be used to search for a pattern in a file or a string and replace it with a new value. Here's how you can use sed to replace a substring in a string:

1. Make sure you have the sed command installed on your system. You can check if it's available by running the following command in your terminal:

which sed

2. Use the following syntax to replace a substring in a string using sed:

new_string=$(echo "$original_string" | sed 's/old_substring/new_substring/')

Here, original_string is the string that contains the substring you want to replace, old_substring is the substring you want to replace, and new_substring is the new substring you want to replace it with.

3. Replace the variables original_string, old_substring, and new_substring with the actual values in your script.

Here's an example that demonstrates the usage of sed to replace a substring in a string:

original_string="Hello, World!"new_string=$(echo "$original_string" | sed 's/World/Universe/')echo "$new_string"  # Output: Hello, Universe!

This example replaces the substring "World" with "Universe" in the original string "Hello, World!".

Related Article: How to Extract Substrings in Bash

Approach 2: Using Parameter Expansion

Another way to replace a substring in a string is by using parameter expansion, a feature provided by the bash shell. Here's how you can do it:

1. Use the following syntax to replace a substring in a string using parameter expansion:

new_string=${original_string//old_substring/new_substring}

Here, original_string is the string that contains the substring you want to replace, old_substring is the substring you want to replace, and new_substring is the new substring you want to replace it with.

2. Replace the variables original_string, old_substring, and new_substring with the actual values in your script.

Here's an example that demonstrates the usage of parameter expansion to replace a substring in a string:

original_string="Hello, World!"new_string=${original_string//World/Universe}echo "$new_string"  # Output: Hello, Universe!

This example replaces the substring "World" with "Universe" in the original string "Hello, World!".

Alternative Ideas and Best Practices

Related Article: Should You Use Numbers in Bash Script Names?

- If you only want to replace the first occurrence of the substring in the string, you can modify the sed command or parameter expansion syntax accordingly.

- The sed command supports regular expressions, so you can use more complex patterns for searching and replacing substrings.

- When using parameter expansion, be cautious about the use of the double slash (//) to replace all occurrences of the substring. If you only want to replace the first occurrence, use a single slash (/) instead.