Heckroth Industries

Why I use cat even though there are more efficient methods

When using a series of commands tied together with pipes I usually start with the cat command. A lot of times when I post a one liner solution on a forum someone will reply that there was no point in starting with cat as it is inefficient. So I decided to put a quick post about why I use cat rather than one of the other methods.

The main reason that I use cat at the start of most strings of pipes is that it is easier to maintain. The logical flow of the data is going from left to right and the files that go into the pipe is easy to spot e.g.

cat /etc/passwd | grep bash | grep -v :x:

We can see here that /etc/passwd gets pushed through grep first to find those lines containing bash. Then those lines are pushed through grep again looking for lines that don’t contain :x: (i.e. non shadowed passwords). This could have been written in a number of different ways.

grep bash /etc/passwd | grep -v :x:
</etc/passwd | grep bash | grep -v :x:

In these examples the first way would be reasonable, but the original file at the start of the pipe is a little hidden tucked away in the first grep command. The second way puts the original file at the start and is very clear, but a typo of > instead of < will destroy the file I am really wanting to read from.

So yes there are more efficient ways to start off a string of pipes, but I like to to use cat as it makes things a bit more obvious than some and less prone to destroying data with a simple typo than others.

Jason — 2011-01-10