diff - macOS


The diff command is used on macOS to compare files and directories line by line, highlighting differences between them. It is essential in various applications such as programming, where it helps in version control by pinpointing exact changes between file versions, and in system administration for verifying changes in configuration files.


The basic syntax of the diff command is as follows:

diff [options] file1 file2

Where file1 and file2 are the files to be compared. diff can also compare the contents of directories:

diff [options] directory1 directory2


Here are some commonly used options and flags for diff:

  • -i — Ignores case differences in file comparisons.
  • -w — Ignores all white space in the files.
  • -b — Ignores changes in the amount of white space.
  • -u, --unified — Displays the differences in a unified format, showing a few lines of context, which is useful for patch files.
  • -r — Recursively compares any subdirectories found.
  • -q, --brief — Reports only when files differ, not the details of the differences.
  • -c, -C NUM, --context=NUM — Output NUM (default 3) lines of copied context.


Example 1: Compare two files and display the differences:

diff file1.txt file2.txt

Example 2: Compare two files, ignoring case:

diff -i file1.txt file2.txt

Example 3: Compare directories recursively:

diff -r dir1/ dir2/

Example 4: Unified format with 5 lines of context:

diff -u -C 5 file1.txt file2.txt

Common Issues

  • File Permission Denied:
    Ensure you have the necessary read permissions for the files or directories you are comparing. Use chmod to change file permissions if necessary.

  • Binary Files: If diff is used on binary files, it may output that files differ without specifying details. Use cmp instead for binary files.


diff is powerful when used in combination with other commands. For example, you can pipe diff output to less for easier readability:

diff file1.txt file2.txt | less

You can also use it in scripts to check for changes and perform actions accordingly:

if diff -q file1.txt file2_backup.txt > /dev/null; then
    echo "No changes detected."
    echo "Changes detected."
  • cmp – Compares two files byte by byte, often used for binary files.
  • patch – Applies diff files to original files, used for modifying sources with updates.

For more detailed information, you can refer to the man diff command in your terminal or visit the GNU diffutils documentation.

By utilizing the diff command effectively, users can maintain better control over file changes, ensure configurations are consistent, and manage code versions efficiently.