When I open my terminal and input the command echo 987654321 | tail -c3, the output is 21.
However, when I create a file named test_tail.sh, write 987654321 into the file, the command tail -c3 test_tail.sh prints 321.
Why these different results? According to the manual, tail -cNUM shows the last NUM bytes of a file. So, I'm curious why echo 987654321 | tail -c3 in the terminal prints 21.
By default, echo appends a newline character (\n) to the output. When you pipe the output of echo 987654321 to tail -c3, it processes the string 987654321\n.
If you don't want the echo command to append a newline character, you can use the -n flag:
echo -n 987654321 | tail -c3 # outputs 321
Note: The -n flag in the echo command is not part of the POSIX standard i.e. some implementations of echo may not support the -n flag. So as mentioned by @Biffen, using the printf command is recommended, which is more portable and adheres to the POSIX standard. Something like:
printf "987654321" | tail -c3