Search and replace

In Groovy, performing search and replace operations on text in a file is quite straightforward and can be done efficiently with built-in methods and Groovy's powerful string manipulation capabilities. Here’s a step-by-step guide on how to search for a specific string in a file and replace it with another string:

1. Read the File

First, you need to read the file. You can use different methods based on the file size. For simplicity, I'll show you how to do it using File.text for smaller files. This loads the entire file content into memory as a single string.

2. Perform the Replacement

Use the replace() or replaceAll() method on the string. replace() is sufficient for literal replacements, while replaceAll() is used for regex-based replacements.

3. Write the Modified Content Back to the File

After modifying the content, write it back to the file using File.text= or another appropriate file writing method.

Here’s how you can put it all together:

// Specify the file path
def filePath = 'path/to/file.txt'

// Read the file content into a string
def fileContent = new File(filePath).text

// Replace the text
// For literal strings:
fileContent = fileContent.replace("oldText", "newText")

// For regex, use:
// fileContent = fileContent.replaceAll("oldTextRegex", "newText")

// Write the modified content back to the file
new File(filePath).text = fileContent

Using a Buffered Approach for Large Files

For larger files, you should consider a buffered approach to avoid high memory usage. This can be done by reading and writing the file line by line and performing replacements as you go:

// Open the original file for reading and create a new file for writing
new File('path/to/file.txt').withReader { reader ->
    new File('path/to/output.txt').withWriter { writer ->
        reader.eachLine { line ->
            // Perform replacement
            String replacedLine = line.replace("oldText", "newText")
            // Write the replaced line to the new file
            writer.writeLine(replacedLine)
        }
    }
}

// Optionally, delete the original file and rename the new file to the original name
def originalFile = new File('path/to/file.txt')
def newFile = new File('path/to/output.txt')
originalFile.delete()
newFile.renameTo(originalFile)

This example reads from one file and writes to another, replacing text as it goes. After completion, it deletes the original file and renames the new file to match the original. This approach keeps memory usage low, making it suitable for very large files.