Question

I read about commands within the { }, happen in the current shell without start a new so The following commands:

for i in {1..50000} ; do echo $i ; done

should works the same as

for i in {1..50000} ; { do echo $i } ; done

but it gives me an error:

zsh: parse error neardo’`

any idea?

Answer 1

I think you mixed-up (and made a typo) two concepts.
The documentation http://www.gnu.org/software/bash/manual/bashref.html
in section 3.2.4.3 says:

   {}
     { list; }
    Placing a list of commands between curly braces causes
    the list to be executed in the current shell context.
    No subshell is created. 
    The semicolon (or newline) following list is required.

They explain it is different from (list; ) with parenthesis (not braces) that would invoke a subshell.
Further in the doc, in 3.5.1, they explain braces expansion (the brace content is expanded as a list of values).

Actually:

for i in {1..50000} 

is a brace expansion: the content between the braces is replaced by a list of integer.

What you wanted to do after the for command, should write:

for i in {1..5000}
do
{ echo $ii ; echo "something else or run a command"; echo "maybe another"; }
done

Notes:

1/ { MUST be followed by a space.

2/ the do command should not be in the brace

3/ the list of commands must end with a semicolon ;