Jake Worth

Save a Command's Output to a File (Unix)

April 09, 2014

One tool that I love allows you to take the output of a terminal command and save it in a file. That command is:

$ command > filename

An example:

$ ps aux > data.txt

This runs the command ps aux and sends the output to a file ‘data.txt’. If that file exists, it will be overwritten; if it doesn’t exist, it will be created. You can check the output using cat:

$ cat data.txt
process status (ps) for all users (a), with owner (u), and processes not attached to the terminal (x)

Another helpful modification is to replace > with >>, like this:

$ ifconfig >> data.txt

This command takes the output of the ifconfig command and appends it to the end of ‘data.txt’. Like the first command, if that file doesn’t exist, it will be created. Inspecting that file once again with cat:

$ cat data.txt
process status (ps) for all users (a), with owner (u), and processes not attached to the terminal (x) + interface configuration (ifconfig)

As you can imagine, the uses of this command are limitless. A test failing on your computer but not failing for a remote contractor? Run the spec, save the output into a text file, and email it to them. Debugging a failing deployment to a hosting provider like Heroku? Run the deploy command, save the output to a text file, and post it in a community forum. Is a test failing only at a certain time of day? Run the >> variant, with your computer clock set to various times, and send all the data to one summary file.

Anytime you are working with a remote person it is much better to provide real, complete data rather than a fragment. In other words, be specific rather than general.

The terminal is one of the most vital tools a developer has. I use it constantly, and my first instinct when approaching any new computer task is to see if it can be done in the terminal. Usually it can, much faster than any alternative.

Besides routine use, one resource I recommend to hone your terminal skills is Zed Shaw’s Command Line Crash Course. It covers all the basic commands in the trademark Zed Shaw style.


Jake Worth

I'm Jake Worth, a developer at Hashrocket based in Chicago. Blog About Now