unwrapdiff Command in Linux
When working on development projects that use diff and patch utilities, you sometimes encounter patch files that have been "word-wrapped". This happens when lines in a diff are broken into multiple lines, either by an email system, printing software, or other formatting tools, to fit display limitations. However, these wrapped patches can be problematic when applying them with standard patch utilities that expect a specific format. Read this tutorial to learn how to use the unwrapdiff command to convert a word-wrapped diff file into a valid, unwrapped patch file.
Table of Contents
Here is a comprehensive guide to the options available with the unwrapdiff command −
- Understanding unwrapdiff Command
- Syntax of unwrapdiff Command
- unwrapdiff Command Options
- Examples of unwrapdiff Command in Linux
Understanding unwrapdiff Command
In software development, a diff (or patch) is a text file that shows the differences between two versions of a file, usually generated by the diff command. These patch files are then fed into the patch utility to update the source code.
A typical diff file contains "hunks" (or sections) marked with context lines and change markers (such as "@@") that tell the patch utility which parts of the file to modify.
Overview of the unwrapdiff Command
The basic purpose of unwrapdiff is to convert a word-wrapped diff file into a valid, unwrapped patch file. It is usually distributed as part of the patchutils package and is maintained by developers such as Tim Waugh. Its fundamental operation involves scanning the diff file, identifying potential wrap points, and rejoining lines based on a set of rules and heuristics.
Syntax of unwrapdiff Command
The syntax for unwrapdiff is straightforward −
unwrapdiff [-v] [file...]
Where,
- [file...] − One or more files containing the wrapped diff. If no file is specified, unwrapdiff reads from standard input.
- -v − Enables verbose mode. This option outputs additional messages to stderr that help you understand how each line is being processed.
unwrapdiff Command Options
Let's examine each option in detail −
The -v Option (Verbose Mode)
When you perform an unwrapping operation, you might not be entirely sure how each line is being modified. The verbose flag (-v) provides insight into what the tool is doing behind the scenes. In verbose mode, unwrapdiff prints a list of lines that it has modified, along with warnings if there is any ambiguity in recombining the wrapped text.
Example usage −
unwrapdiff -v patchfile.diff
The output might include lines such as −
- Warning − Hunk starting at line 55 may have been wrapped unexpectedly.
- Reassembling line − "diff --git a/file" with the following continuation.
Standard Options: --help and --version
The --help flag is standard among Linux command-line tools. It provides a short usage message along with a brief description of available options.
Let's take a look at some examples −
Displaying help −
unwrapdiff --help
Checking the version −
unwrapdiff --version
The help message typically outlines the command's purpose, showing the syntax and explaining the options available.
Examples of unwrapdiff Command in Linux
Understanding the internal mechanism of unwrapdiff can help you decide when and how to use it effectively. These limitations mean you should always review the output of unwrapdiff especially in verbose mode before applying the patch with the patch command.
To illustrate how unwrapdiff works in practice, let's walk through several examples that include both common use cases and scenarios that push the limits of the unwrapping process.
A Simple Word-Wrapped Patch Example
Imagine you receive a patch file that was emailed and, as a result, has been word-wrapped. Consider the following excerpt from a hypothetical patch file −
Before running unwrapdiff −
a/example.c 2025-04-26 00:00:00.000000000 +0000
+++ b/example.c 2025-04-26 00:01:00.000000000 +0000
@@ -1,4 +1,4 @@
-include <stdio.h>
+include <stdio.h>
-int main(void) {
- printf("Hello, world!\n");
- return 0;
-}
+int main(void) {
+ printf("Hello, world! This patch has been
+ word-wrapped incorrectly.\n");
+ return 0;
+}
Notice that in the modified version, the line containing the printf statement has been split into two lines by the email system's word wrap.
Running unwrapdiff −
unwrapdiff -v wrapped_patch.diff > unwrapped_patch.diff
After running unwrapdiff −
a/example.c 2025-04-26 00:00:00.000000000 +0000
+++ b/example.c 2025-04-26 00:01:00.000000000 +0000
@@ -1,4 +1,4 @@
-include <stdio.h>
+include <stdio.h>
-int main(void) {
- printf("Hello, world!\n");
- return 0;
-}
+int main(void) {
+ printf("Hello, world! This patch has been word-wrapped incorrectly.\n");
+ return 0;
+}
Explanation − Here, unwrapdiff detected that the printf line was split and reassembled it into one continuous line, inserting a space if necessary (depending on the exact heuristic outcome). The verbose output would detail this correction, helping you confirm that the patch is now properly formatted for application.
Handling Multiple Files
unwrapdiff can process more than one patch file at a time. If you have several wrapped patch files in a folder, you can simply list them as arguments −
unwrapdiff -v patch1.diff patch2.diff patch3.diff
Each file will be processed individually. The verbose output will indicate which patch file is being processed and note any ambiguities or modifications that were made. This bulk processing is essential when dealing with large patch series or when automating legacy patch corrections.
Using Standard Input and Redirection
If you have a patch file generated by another tool or one that is output from a command pipeline, you may not have a physical file on disk. In such cases, unwrapdiff reads from the standard input. For example −
cat wrapped_patch.diff | unwrapdiff -v > unwrapped_patch.diff
This command pipes the contents of wrapped_patch.diff into unwrapdiff, which then outputs the corrected patch to unwrapped_patch.diff.
Integration with the patch Command
After unwrapping, the newly formatted patch file is typically applied using the patch command. However, note that because the unwrapping process may slightly modify the spacing, you might have to use the -l (ignore whitespace differences) flag with the patch command to ensure a smooth application −
patch -l < unwrapped_patch.diff
Using -l instructs patch to be lenient about whitespace differences when applying the patch, which aligns with the modifications that unwrapdiff might have introduced.
Conclusion
The Linux unwrapdiff command is a powerful and straightforward tool designed to address a very specific, yet common, problem in the software development workflow: reassembling word-wrapped patch files.
By scanning each line for potential breaks, employing intelligent heuristics to determine where spaces should be inserted, and offering a verbose mode for detailed feedback, unwrapdiff ensures that patches are restored to a state where they can be applied confidently with the standard patch command.