How can I shuffle the lines of a text file on the Unix command line or in a shell script?

Question

I want to shuffle the lines of a text file randomly and create a new file. The file may have several thousands of lines.

How can I do that with cat, awk, cut, etc?

Answer 1

You can use shuf. On some systems at least (doesn't appear to be in POSIX).

As jleedev pointed out: sort -R might also be an option. On some systems at least; well, you get the picture. It has been pointed out that sort -R doesn't really shuffle but instead sort items according to their hash value.

^{[Editor's note: sort -R almost shuffles, except that duplicate lines / sort keys always end up next to each other. In other words: only with unique input lines / keys is it a true shuffle. While it's true that the output order is determined by hash values, the randomness comes from choosing a random hash function - see manual.]}