Скачать или смотреть How to compare and recursively modify strings in Bash

Learn how to effectively compare and modify strings in Bash, even without recursion, using simple loops and parameter expansion
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How to Compare and Recursively Modify Strings in Bash

Bash scripting can be a bit challenging for those accustomed to programming languages like Python, particularly when it comes to string manipulation. In this guide, we’ll tackle a common problem: how to compare two strings character by character, modifying one based on the other. Let's break this down!

The Problem

You have:

Two uppercase strings of the same length.

An unchangeable reference string (string1).

A modifiable string (string2) that you want to alter based on string1.

Example Input

string1: CYVFGDDAS

string2: CRFDGVEAT

What You Want to Achieve

You need to:

Compare the characters of both strings starting from the first position.

If characters at the same index are different, replace the character in string2 with the character from string1.

Save the modified string2 along with a substitution code in a file.

Repeat this process until all characters have been processed.

Substitution Code Explained

The substitution code needs to follow this format:

Y: Character from string1 replacing the one in string2.

A: A constant character included in all replacements.

2: The index where the replacement occurred.

V: The character from string2 that was replaced.

The Solution

Though you might initially think recursion is necessary for such a task, you can achieve this with iteration in Bash. The following Bash script demonstrates how to do this efficiently.

Bash Script Example

[[See Video to Reveal this Text or Code Snippet]]

Breaking Down the Script

Initialization: The two strings s1 and s2 are defined.

Looping through Characters: A for loop iterates over the index of the characters in the strings:

[[See Video to Reveal this Text or Code Snippet]]

Comparing Characters: The if statement checks if characters at the same position in both strings are different:

[[See Video to Reveal this Text or Code Snippet]]

Outputting Results: If they're different, it prints the current modified string and the corresponding substitution code.

Sample Output

Given the input strings, running this script will yield:

[[See Video to Reveal this Text or Code Snippet]]

Conclusion

With this Bash script, you’ve learned how to compare and modify strings without needing recursion. By utilizing parameter expansion and a simple loop, you can effectively manage string manipulations in Bash, similar to what you might do with Python.

Feel free to adapt the script to your specific needs, including redirecting the output to a file as required for your project!

If you have any questions or need further assistance, feel free to ask.