Create a large empty file for testing

8 September 2022   0 comments   Linux

Because I always end up Googling this and struggling to find it easily, I'm going to jot it down here so it's more present on the web for others (and myself!) to quickly find.

Suppose you want to test something like a benchmark; for example, a unit test that has to process a largish file. You can use the dd command which is available on macOS and most Linuxes.

▶ dd if=/dev/zero of=big.file count=1024 bs=1024

▶ ls -lh big.file
-rw-r--r--  1 peterbe  staff   1.0M Sep  8 15:54 big.file

So the count=1024 creates a 1MB file. To create a 500KB one you simply use...

▶ dd if=/dev/zero of=big.file count=500 bs=1024

▶ ls -lh big.file
-rw-r--r--  1 peterbe  staff   500K Sep  8 15:55 big.file

It creates a binary file so you can't cat view it. But if you try to use less, for example, you'll see this:

▶ less big.file
"big.file" may be a binary file.  See it anyway? [Enter]

big.file (END)


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