Shell – Difference between echo and print in the Korn shell

If the value of $FOO is a single word that doesn't contain a wildcard character \[*?, then the two are identical.

If $FOO is unassigned, or empty, or more than one word (i.e., contains whitespace or $IFS), then the unquoted version is a syntax error. If it happens to be just the right sequence of words (such as 0 -eq 0 -o false), the result could be arbitrary. Therefore, it is good practice to always quote variables in shell scripts.

Incidentally, "true" does not need to be quoted.

`date` will just expand to the output of the date command. However, it removes extra space characters at places where there are more than one consecutive space character in the output. (This is because the command substitution is subject to word splitting, and because of how the echo command handles multiple arguments.)

In "`date`", the double quotes are weak quotes, so they will expand variables (try "$PWD") and perform command substitution. The result of the expansion is passed as a single argument to the echo command, with any consecutive spaces included: that is, word splitting is not performed.

In '`date`', the single quotes are stronger quotes, so they will not allow expansion of variables or command substitution within them.

Refer this link for more explanation.

Edited the first point as correctly pointed by Michael Suelmann in the comment below.