diffstat

Display changes in a histogram

$ diff [path/to/file1] [path/to/file2] | diffstat

$ diff [path/to/file1] [path/to/file2] | diffstat -t

diffstat [options] [file...]
Most commonly used by piping diff output: diff [options] | diffstat [options]

-c
    Show cumulative line counts for additions and deletions across all files processed.

-f
    Specify the output format. Common formats include 'brief' (default: filename, changed lines, histogram) or 'total' (just total lines changed).

-g
    Always show the graphical histogram, even if other options might suppress it (often default behavior).

-h
    Display a help message with command usage and options, then exit.

-l
    Do not truncate long filenames in the output, showing full paths.

-n
    Do not show the graphical histogram; print numeric totals only for additions, deletions, and changed lines.

-p
    Process the input as a patch file, which often contains additional header information (often the default for piped input).

-R
    Reverse the interpretation of additions and deletions. Lines previously marked as added will be counted as deleted, and vice-versa.

-v
    Display version information of the diffstat utility and exit.

-w
    Set the maximum width of the output line, specifically controlling the width of the histogram.

--files
    Print only filenames and the total count of changed lines per file, omitting the detailed histogram.

--total
    Print a grand total line at the end, summarizing all additions, deletions, and total changed lines across all files.

diffstat reads the output of the diff command or a patch file and provides a concise summary of the changes. For each file, it typically displays the filename, the number of lines added, the number of lines deleted, and an ASCII-based graphical histogram representing these changes. This utility is invaluable for quickly understanding the scope and nature of modifications across multiple files in a patch or a large change set, offering a high-level overview without the need to review the full, detailed diff output. It helps in assessing the impact of code changes at a glance, making it easier to gauge the size and complexity of revisions.

diffstat relies on receiving input in a standard diff format (e.g., unified, context, or normal diff). If the input is malformed or not recognized as a valid diff or patch, it may produce incorrect or no output. It only summarizes existing differences; it does not generate the diffs themselves. The graphical histogram is ASCII-based, so its visual appearance might vary slightly depending on the terminal emulator and font configuration.

The most common and effective way to use diffstat is by piping the output of a diff command (or any command producing diff-like output) directly into it. This allows for immediate summarization of changes.
Example 1: Summarizing a traditional file diff:
diff -u file1.c file2.c | diffstat

Example 2: Summarizing changes in a Git repository:
git diff | diffstat

Due to its ability to process standard input and produce structured, human-readable output, diffstat is highly versatile for integration into shell scripts. It can be used as a component in automated workflows for code review, generating concise change reports, or as part of continuous integration/delivery pipelines where a quick, high-level overview of modifications is beneficial.

diffstat is a classic utility, typically distributed as part of the patchutils package, which provides a suite of tools for manipulating and applying patch files. Its development arose from the fundamental need to quickly digest and understand code changes encapsulated in traditional diff files – the predominant method of sharing code modifications before the widespread adoption of modern distributed Version Control Systems (VCS) like Git. While many contemporary VCS tools now offer built-in summary functionalities (e.g., git diff --stat), diffstat remains a robust and independent tool for analyzing plain diff output, particularly useful in shell scripting, legacy systems, or when dealing with generic patch formats.

diff(1), patch(1), git-diff(1)