[Chapter 33] 33.7 ed/ex Batch Edits: Avoid Errors When No Match

33.7 ed/ex Batch Edits: Avoid Errors When No Match

Q: My Bourne shell script ( 44.1 ) calls ed to edit a set of files:

= for << \	site=something cmty=somethingelse for i in file1 file2 file3 do ed $i << end 1,\$s/pat1/$site/g 1,\$s/pat2/$cmty/g w q end done

Q: It works fine except when one of the files does not contain pat1 . ed doesn't update that file, even though it could have matched pat2 . The other files are edited as they should be.

A: On an error - including "no matches" - ed attempts to discard any unread commands. If you are running ed "by hand" this has no effect, but if its input is from a file, this makes EOF -d-of-file) the next thing it sees. You could remove the q command and you would see the same behavior, as ed automatically quits at end-of-file.

There is a simple workaround. Unlike the s command, the global command g does not report an error if no lines match. Thus:

ed - $i << end
g/pat1/s//$site/g
g/pat2/s//$cmty/g
w
end

The - (dash) flag suppresses the two numbers that ed normally prints when reading and writing files. These are the number of characters in the file, and are usually irrelevant. [As Chris explained, the q in the original script isn't needed. -JP ]

- CT in comp.unix.questions on Usenet, 16 May 1989