freeze when calling any shell command

To recreate the problem:

1. Create an .bashrc_emacs file :

# -*- shell-script -*- export PATH="$PATH":~/SYNCHRO/bin/ # put the path to where net.ip.private is export BOOTTIME=$(sys.boottime) 

2. Create and chmod +x the sys.boottime script:

 #!/bin/bash last reboot | awk 'NR == 1 {print $5,$6,$7,$8}' 

3. Evaluate this line of elisp code:

 (setenv "BASH_ENV" (expand-file-name "~/.bashrc_emacs")) 

This should load the bashrc_emacs file prior to executing any shell command with M-!

4. Then call any shell command, like a simple echo "hello world!"

In my case, it simply freezes. if I replace this line in the bashrc_emacs file:

export BOOTTIME=$(sys.boottime) 

with this line:

export UP=$(last reboot | awk 'NR == 1 {print $5,$6,$7,$8}') 

then everything works right.
it only freezes when I use that script,
which is in the path by the way.
you can even comment that line:

# export UP=$(last reboot | awk 'NR == 1 {print $5,$6,$7,$8}') # or # export BOOTTIME=$(sys.boottime) 

and M-! echo $BOOTTIME which should return last time your machine booted.

Any help appreciated.
This is Emacs 24 running on linux.