BASH: Log stdout and stderr to file and display on screen -> get correct error code

Question

I want to log stdout and stderr with timestamp to a log file and view it on screen. So I redirect stderr to stdout, add the timestamp with awk und tee it to log file. But there is a problem to get the correct error code.

Here an example without logging:

$ less notexists.txt
notexists.txt: No such file or directory
$ echo $?
1

The error code is correct

Here the example with logging:

$ less notexists.txt 2>&1 | awk '{ print strftime("[%Y-%m-%d %H:%M:%S]"), $0; fflush(); }' | tee -a log.txt
[2017-10-23 17:19:59] notexists.txt: No such file or directory
$ echo ${PIPESTATUS[*]}
0 0 0

The error codes of all three sections are 0, but in the first section should be a 1. I think the problem could be the redirection of stderr.

Is there a solution to log stdout and stderr with timestamp to a log file and view it on screen and get the correct error code?

Is it possible to duplicate stderr instead of redirect it?

The issue is with less having something other than a terminal as its standard output; try { less noexists.txt; echo $?; } | cat. — chepner
– chepner, Commented Nov 3, 2017 at 9:09

chepner · Accepted Answer · 2017-11-03 09:37:32Z

Apparently, less doesn't have a non-zero exit status if its standard output is not a terminal. If you force it

$ less notexists.txt  2>&1 > /dev/tty | awk '{ print strftime("[%Y-%m-%d %H:%M:%S]"), $0; fflush(); }' | tee -a log.txt
#                          ^^^^^^^^^^

you'll get the expected exit status, although you'll no longer get the standard output in your log file.

Here is, I think, the relevant code from less v487:

if (!is_tty)
        {
                /*
                 * Output is not a tty.
                 * Just copy the input file(s) to output.
                 */
                SET_BINARY(1);
                if (nifile() == 0)
                {
                        if (edit_stdin() == 0)
                                cat_file();
                } else if (edit_first() == 0)
                {
                        do {
                                cat_file();
                        } while (edit_next(1) == 0);
                }
                quit(QUIT_OK);
        }

So when standard output is not a terminal, less simply behaves like cat, except it ignores any errors trying to open its input. Regardless of what happens, it just exits 0.

Arguably, this is a bug, but I have spent all of 2 minutes looking at the source code, so I don't know if there is a rationale for this behavior.

I've submitted a bug report; I'll report back with the maintainer's thoughts.

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