Why am I observing different behaviour of echo?

Question

I am a bash beginner and observed the below behavior of echo

#!/bin/bash

x=" hello"

echo $x
echo "$x"

Now when I run the above code I get

ronnie@ronnie:~$ bash test.sh
hello
 hello
ronnie@ronnie:~$

So, can someone explain to me why whitespace in first case is not present in output and also points me to the documentation where this behavior is defined.

Answer 1

It is not the echo behavior. It is a bash behavior. When you use echo $x form the bash get the following command to process (treat ␣ as space):

echo␣␣hello

Then this command is tokenized and bash get two tokens: echo and hello thus the output is just hello

When you use the echo "$x" form then the bash has the following at the input of tokenizer:

echo␣"␣hello"

thus it has two tokens echo and ␣hello, so the output is different.

Answer 2

The reason you see different output is because the echo[1 space]Hello line is syntactically equal to echo[5 spaces]Hello. The whitespace is ignored, and the word 'Hello' is treated as the argument to echo. The first line, in it's simplest form, is much the same as if you had said echo "Hello". In the second line, you have explicitly included a leading space as part of the argument to echo, with echo " Hello".

In the first line, you are passing a 5 character string to echo, and in the second line you are passing a 6 character string to echo.

So, in fact, the behavior of echo is the same in both instances, it's just the string being passed to echo that changes.