The read (r) and write (w) commands allow you to work directly with files. Both take a single argument, the name of a file. The syntax follows:
The read command reads the contents of file into the pattern space after the addressed line. It cannot operate on a range of lines. The write command writes the contents of the pattern space to the file.
You must have a single space between the command and the filename. (Everything after that space and up to the newline is taken to be the filename. Thus, leading or embedded spaces will become part of the filename.) The read command will not complain if the file does not exist. The write command will create a file if it does not exist; if the file already exists, the write command will overwrite it each time the script is invoked. If there are multiple instructions writing to the same file in one script, then each write command appends to the file. Also, be aware that you can only open up to 10 files per script.
The read command can be useful for inserting the contents of one file at a particular place in another file. For instance, let’s say that there is a set of files and each file should close with the same one- or two-paragraph statement. A sed script would allow you to maintain the closing separately while inserting it as needed, for instance, when sending the file to the printer.
sed '$r closing' $* | pr | lp
The $ is an addressing symbol specifying the last line of ...