UNIX for Dummies Questions & Answers

I am trying to use join with the -e option to join columns in two files, with the -e option to replace empty fields with periods. I use the command:

Code:

join -e "." -a1 -a2 a.txt b.txt

But the -e option does not seem to work, because no periods appear (nor x's if I use -e "x" instead) when blank cells result. Am I doing something wrong? (I am using Mac OS X's Terminal.)

Here is a transcript:

Code:

$ cat a.txt
1 "a bc" 5
2 "asbdfghjksdlhwugyhe" 4
3 "as ds wd sdw swdw wd" 5
8 "french" 3
$ cat b.txt
1 "abc" 3
2 "def" 2
3 "gh i" 1
4 "fred"
$ join -e "." -a1 -a2 a.txt b.txt
1 "a bc" 5 "abc" 3
2 "asbdfghjksdlhwugyhe" 4 "def" 2
3 "as ds wd sdw swdw wd" 5 "gh i" 1
4 "fred"
8 "french" 3

The -e option to joing seemingly should yield .'s in the output lines beginning 4 and 8, but did not. Apologies if I am missing the obvious -- I've tried all the man pages, web pages, etc. I can think of and haven't figured this one out. (I am preparing to do this on circa 500MB sorted files.)

Any suggestions will be much appreciated!!!

I think the -e option is only to be used with the -o option, e.g...

Code:

$ join -e "." -a1 -a2 -o '0 1.2 1.3 2.2 2.3' a.txt b.txt
1 "a bc" "abc" 3
2 "asbdfghjksdlhwugyhe" 4 "def" 2
3 "as ds "gh i"
4 . . "fred" .
8 "french" 3 . .

...which is probably not what you want.

Thanks Ygor, That was just what I was missing; -e requires -o. The -o option requires knowing the number of fields in files a.txt and b.txt, which ideally one need not know (join could count them), but since I know these numbers the -o solution works fine for me. Thanks again.