Using BSD jot

Most every Linux system comes with GNU seq (a utility to generate sequences of numbers or characters). However, a much older utility – and more flexible one – is the underutilized and unknown utility, jot. Every BSD system, including MacOS X, will come with jot (and not with seq).

Unfortunately, commercial UNIX tends to come with neither. So unless you are using an open source operating system, both of these utilities are unavailable. This is unfortunate.

To install jot under Debian Linux and variants (including Ubuntu), install the athena-jot package. FreeBSD, OpenBSD, and MacOS X should already have jot installed out of the box.

Using jot is easy:

  • Generate a count 1 to 6: jot 6
  • Generate a count 5 to 10: jot 6 5
  • Print “y” 100 times: jot -b y 100
  • Generate a count 1 to 6 separated by commas: jot -s "," 6
  • Generate abc1 to abc20: jot -w abc 20

This only begins to touch on the capabilities of jot. It can also generate random numbers and random character data.

In fact, to generate a large file (5Gb in this case), try this:

jot -r -c -s '' $(( 1024 * 1024 * 5 )) > file.5gb

If you do install the athena-jot package on Ubuntu or Debian, you may want to do this:

cd /usr/share/man/man1
sudo ln -s athena-jot.1.gz jot.1.gz

For some reason, the package – and the manpage – are called athena-jot but the utility is actually jot (not athena-jot). The FreeBSD man page for jot(1) (PDF)has more details.

Using Perl to make big files

A while ago, I talked about making big files. This was, by nature, UNIX-specific – that’s what I deal with all day, and the focus of this blog.

However, not all systems are UNIX (or Linux) – and not all the systems I deal with all day long are UNIX or Linux. However, perl is everywhere – and can be used quite easily to generate large files whatever you might be on.

For example, to make a 5M file, try this:

perl -e "open(FD, 'myfile'); print FD 'x' x (1024 * 1024 * 5);"

If you are inside of vim (a vi-clone which also runs everywhere), try this:

:!perl -e "print '-' x (1024 * 1024 * 5);"

This gives you a single line (5 megabytes in size). To make multiple lines:

:!perl -e 'for ($i = 1; $i < 500; $i++) { print "x" x 39, "\n"; };'

This makes 500 lines of 40 characters each (including single-character line terminator). If the system line terminator is two characters, then use 38 instead of 39. In total, this gives 19000 characters (about 18 kilobytes).

Perl is quite useful for creating portable scripts – but is by no means the only one. The ideas given here carry over to other languages that may be available. For instance, tcl and python and ruby are also available in other environments, and can do the same things as perl does here.

Of course, perl’s repetition operator ‘x’ makes it particularly easy here.

Update: corrected perl one-liner.