In the example bellow I'll write the solution that I used:
The scenario: I want to copy file from a server using sh script:
#!/usr/bin/expect
$PASSWORD=password
my_script=$(expect -c "spawn scp userName@server-name:path/file.txt /home/Amine/Bureau/trash/test/
expect \"password:\"
send \"$PASSWORD\r\"
expect \"#\"
send \"exit \r\"
")
echo "$my_script"