What does && do in redirecting an output to a file?

Question

I found a bash script that lists all files with a blank line at the beginning or end of the file.

for f in `find . -type f`; do 
  for t in head tail; do 
    $t -1 $f  |egrep '^[  ]*$' >/dev/null && echo "blank line at the $t of $f" ;
  done; 
done

I would like to pass the output to a file. I changed the echo line to:

$t -1 $f  |egrep '^[  ]*$' >/dev/null && echo "blank line at the $t of $f" > blank_lines.log

But this didn't work.

I would like to ask what the symbol && does and why the above line does not pass the output to the file.

Answer 1

This does not redirect output it adds another command to execute if and only if the first one succeeded. I.e command1 && command2 means execute command1 and if it is successful execute command2. Also the result of executing this statement is success if and only if both commands succeeded.