How to Get File Checksum by Command Line on macOS

In today’s digital world, ensuring the integrity of files is paramount. Whether you’re downloading software, transferring important documents, or verifying backups, it’s crucial to confirm that files have not been tampered with or corrupted. One effective way to do this is by computing a checksum—a unique string of characters generated from the contents of a file. This checksum serves as a digital fingerprint, allowing you to verify the authenticity and integrity of the file. In this blog post, we’ll explore how to obtain file checksums using the command line on macOS.

What is a Checksum?

Before we dive into the specifics of generating a checksum on macOS, let’s briefly discuss what a checksum is. A checksum is a cryptographic hash function that takes input data (in this case, a file) and produces a fixed-size string of characters, typically represented in hexadecimal format. This string is unique to the input data. Even a small change in the input data results in a significantly different checksum. Therefore, comparing checksums is an effective way to detect any alterations or corruption in files.

Using the shasum Command

On macOS, the shasum command-line utility is commonly used to compute checksums. The shasum command can calculate checksums using various cryptographic hash functions, including SHA-1, SHA-256, SHA-384, and SHA-512. Here’s how to use shasum to generate a checksum for a file:

  1. Open Terminal: Launch the Terminal application on your macOS. You can find it in the Utilities folder within the Applications folder, or simply use Spotlight search to locate it.

  2. Navigate to the Directory: Use the cd command to navigate to the directory containing the file for which you want to compute the checksum. For example, if your file is located in the Downloads folder, you can navigate there by typing:

cd ~/Downloads
  1. Compute the Checksum: Once you’re in the appropriate directory, use the shasum command followed by the filename to compute the checksum. For example, to generate a SHA-256 checksum for a file named example_file.txt, you would type:
shasum -a 256 example_file

Replace example_file with the name of your file.

  1. View the Checksum: After executing the command, shasum will output the computed checksum along with the filename. The checksum is displayed as a hexadecimal string.

Verifying Checksums

Once you have computed the checksum for a file, you can compare it against a known, trusted checksum to verify the integrity of the file. If the checksums match, it’s highly likely that the file has not been altered or corrupted. However, if the checksums differ, it indicates that the file has been modified or damaged.

Conclusion

In conclusion, computing checksums using the command line on macOS is a straightforward process, thanks to the shasum utility. By generating checksums for your files, you can ensure their integrity and authenticity, providing peace of mind in an increasingly digital world where data security is paramount. Whether you’re a software developer, system administrator, or everyday user, incorporating checksum verification into your workflow is a valuable practice for safeguarding your data.

Next time you download a file or transfer important documents, consider generating and verifying checksums to ensure that your files remain untampered and intact. It’s a small step that can make a big difference in maintaining the integrity and security of your digital assets.