Why does this command work for logging script output?

Question

This command does not store the output of my script in the log file:

. myscript.sh | tee -a log_file.log

However this next command does store the output in the log file.

. myscript.sh 2>&1 | tee -a dash_log.log

Why does the second one work and not the first? AFAIK the only difference is that I have told bash to redirect stderr to stdout, and it should not make any difference to what happens with stdout. Yet that first command would not even store the 'error-less' version of stdout in the log file.

And in case it matters: I'm on Ubuntu 12.04 hosted on AWS

EDIT: This was caused by erroneous assumptions of how wget outputs messages. See https://stackoverflow.com/questions/13066518/why-does-wget-output-to-stderr-rather-than-stdout and http://www.gnu.org/software/wget/manual/html_node/Logging-and-Input-File-Options.html

Answer 1

It seems likely that your script is writing most or all of it's output to stderr. This is easy to test

myscript.sh > std.out
myscript.sh 2> err.out

then look at the contents of each file and be educated.

---

I doubt it - the only output from the script comes from calls to wget

Instead of doubting, again this is easy to test

$ wget http://serverfault.com >std.out
--2013-09-09 07:06:25--  http://serverfault.com/
Resolving serverfault.com... 198.252.206.16
Connecting to serverfault.com|198.252.206.16|:80... connected.
HTTP request sent, awaiting response... 200 OK
Length: 51867 (51K) [text/html]
Saving to: “index.html.6”

100%[=================================================>] 51,867   231K/s  in 0.2s

2013-09-09 07:06:26 (231 KB/s) - “index.html.6” saved [51867/51867]

See, output still gets written to the terminal then try

 $ wget http://serverfault.com 2>err.out
 $

Q.E.D.

The wget command writes it's output to stderr not stdout.

Answer 2

Would probably need to see the code but it is probably due to your code writing out to stderr.