sed edit file in place

Question

I am trying to find out if it is possible to edit a file in a single sed command without manually streaming the edited content into a new file and

Answer 1

If you are replacing the same amount of characters and after carefully reading “In-place” editing of files...

You can also use the redirection operator <> to open the file to read and write:

sed 's/foo/bar/g' file 1<> file

See it live:

$ cat file
hello
i am here                           # see "here"
$ sed 's/here/away/' file 1<> file  # Run the `sed` command
$ cat file
hello
i am away                           # this line is changed now

From Bash Reference Manual → 3.6.10 Opening File Descriptors for Reading and Writing:

The redirection operator

[n]<>word

causes the file whose name is the expansion of word to be opened for both reading and writing on file descriptor n, or on file descriptor 0 if n is not specified. If the file does not exist, it is created.