What is the difference between `sed -i -e` and `sed -ie`?

Question

What is the difference between sed -i -e and sed -ie ? It's not very clear from help sed --help

  -e script, --expression=script
                 add the script to the commands to be executed

In second case it creates some backup file?

In general Unix utils do not permit to combine flags?

Just an example to show what is happening:

echo "bla" > 1.txt
cat 1.txt
bla
sed -i -e 's:bla:blakva:g' 1.txt
cat 1.txt
blakva
sed -ie 's:bla:blakva:g' 1.txt
cat 1.txt
blakvakva
*Note: also 1.txte is created, containing
cat 1.txte
blakva

Also not still sure what is -e doing in my example, because sed -i 's:bla:blakva:g' 1.txt works too.

Answer 1

When you give sed -i -e, sed sees two options.

But, When you give sed -ie, sed sees -i option only with suffix as e. That is the reason you got file backup with e suffix.

From man sed:

-i[SUFFIX], --in-place[=SUFFIX]

edit files in place (makes backup if SUFFIX supplied)

Answer 2

Option -i means that it modify in-place the file you are sed-ing. Otherwise sed just show what modification were done. If you add a suffix after -i (e.g -i.bck) it will backup your input file then add the suffix provided.

Option -e allow you to provide sed script instead of command line arguments.