Ubuntu – the difference between “cat < filename” and “cat filename”

catcommand lineredirect

The simplest way to display file contents is using the cat command:

cat file.txt

I can get the same result using input redirection:

cat < file.txt

Then, what is the difference between them?

Best Answer

There is no difference from a user point of view. These commands do the same thing.

Technically the difference is in what program opens the file: the cat program or the shell that runs it. Redirections are set up by the shell, before it runs a command.

(So in some other commands--that is, not the command shown in the question--there may be a difference. In particular, if you can't access file.txt but the root user can, then sudo cat file.txt works but sudo cat < file.txt does not.)

You can use either one that is convenient in your case.

There are almost always many ways to get the same result.

cat accepts a file from arguments or stdin if there are no arguments.

See man cat:

SYNOPSIS
       cat [OPTION]... [FILE]...

DESCRIPTION
       Concatenate FILE(s) to standard output.

       With no FILE, or when FILE is -, read standard input.
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