What does `od -c` command show?

Great question! The command od stands for "Octal Dump", but when you add the -c flag, it becomes much more readable for humans.

What od -c does:

It displays the contents of a file (or input) as backslashed characters.

Specifically:

1. Visible Characters: Letters, numbers, and symbols (like A, z, !) are shown exactly as they are.
2. Special/Hidden Characters: Characters that you usually can't "see" are shown as escape sequences. The most common ones are:
   • \n: Newline (takes you to the next line)
   • \t: Tab
   • \r: Carriage return
   • \0: Null character

Why did I suggest it for tail -c1?

When you ran tail -c1 /tmp/hello, the output looked empty because the last byte was a Newline.

If you run:

tail -c1 /tmp/hello | od -c

The output will look something like this:

0000000  \n
0000001

• The \n confirms that the last byte is indeed a newline character.
• The 0000000 and 0000001 on the left are just the "offset" (counting how many bytes into the file you are).

Summary:

od -c is like a "X-ray set of glasses" for your files. It allows you to see exactly what is inside, including the formatting characters that are normally invisible to the naked eye. It's a lifesaver when you're trying to figure out why a file or a script isn't behaving correctly!