sed script. How does it work?

Shell Programming and Scripting
1

I'm using this command
sed -e "s/'/'/g" -e 's/"/"/g' -e 's/&/\&/g' myfile.txt

My question is does this command reads file 3 times applying different replacement each time or it reads it only once and do 3 replacements at the same time?
My concern is, since I have big files (1 MB or more) that if its' first case - it will be very slow as list of different replacements grow. Have 3 now but can have 15 in a future!? Now it takes 45 minutes for 1mb file.

Thank you

2

the latter according to 'man sed'

     -e script script is an edit command  for  sed  .  See  USAGE
               below  for  more  information  on  the  format  of
               script. If there is just one -e option and  no  -f
               options, the flag -e may be omitted.

     -f script_file
               Take the script from script_file. script_file con-
               sists of editing commands, one per line.

     Multiple -e and -f options may be  specified.  All  commands
     are  added  to the script in the order specified, regardless
     of their origin.
3

Thanks, this explains it :
$ man sed
-----
A script consists of editing commands, one per line, of the following
form:

          [address[,address]]function[arguments ]

   In normal operation, sed cyclically copies a line of input into a
   pattern space \(unless there is something left after a D command\),
   applies in sequence all commands whose addresses select that pattern
   space, and at the end of the script copies the pattern space to the
   standard output \(except under -n\) and deletes the pattern space.