5.3. Why does my DOS version of sed process a file part-way through and then quit?

First, look for errors in the script. Have you used the -n switch without telling sed to print anything to the console? Have you read the docs to your version of sed to see if it has a syntax you may have misused? (Look for an N or H command that gathers too much.)

Next, if you are sure your sed script is valid, a probable cause is an end-of-file marker embedded in the file. An EOF marker (SUB) is a Control-Z character, with the value of 1A hex (26 decimal). As soon as any DOS version of sed encounters a Ctrl-Z character, sed stops processing.

To locate the EOF character, use Vern Buerg's shareware file viewer LIST.COM <https://www.buerg.com/list.html>. In text mode, look for a right-arrow symbol; in hex mode (Alt-H), look for a 1A code. With Unix utilities ported to DOS, use 'od' (octal dump) to display hexcodes in your file, and then use sed to locate the offending character:

       od -txC badfile.txt | sed -n "/ 1a /p; / 1a$/p"

Then edit the input file to remove the offending character(s).

If you would rather NOT edit the input file, there is still a fix. It requires the DJGPP 32-bit port of 'tr', the Unix translate program (v1.22 or higher). GNU od and tr are currently at v2.0 (for DOS); they are packaged with the GNU text utilities, available at

       ftp://ftp.simtel.net/pub/simtelnet/gnu/djgpp/v2gnu/txt20b.zip
       https://www.simtel.net/gnudlpage.php?product=/gnu/djgpp/v2gnu/txt20b.zip&name=txt20b.zip

It is important to get the DJGPP version of 'tr' because other versions ported to DOS will stop processing when they encounter the EOF character. Use the -d (delete) command:

       tr -d \32 < badfile.txt | sed -f myscript.sed