This is a quick explanation of a way to repeat text in Unix using seq and xargs.

For a recent task I needed to create a long text document for testing purposes.

In this case it was enough to just copy the same text multiple times.

After a quick research I found a neat way of doing this on the command line.

Let’s assume we have a file called short.txt and want to copy its content 100 times into a file called long.txt. We can do this with the following line:

seq 100 | xargs -Inone cat short.txt > long.txt

Let me explain:

  1. seq 100 outputs the numbers from 1 to 100 each on one line.
  2. | forwards all the output of the first command to the following one.
  3. xargs gets all the output from seq and takes another command as argument which it will run for each line of its input.
  4. -Inone sets the -I flag for xargs with a value of “none”. This will replace the string “none” in the following command with the line of input xargs passes to it. By setting I to “none” and not using “none” anywhere in the following command, we tell xargs to just ignore the previous input.
  5. cat short.txt is the command we give as argument to xargs. This command will be run 100 times now. cat stands for concatenate. We give it a file name as argument and all it does is to output the content of this file.

  6. With seq 100 | xargs -Inone cat short.txt so far, we output 100 times the content of short.txt.

  7. The last part, > long.txt takes this output now and redirects it into the file long.txt.

That’s all.

There are many other Unix tools you could use to achieve this task, but I like this solution in particular because it uses only really basic Unix tools. There is no need to learn some more cryptic, tool specific syntax like with sed or printf.