How to run a command while logging output to a file?

Question

I have a console application that needs to be run as part of the deployment of a new application version on my server.

This console application is designed to output to the console, and cannot be changed.

I'd like to run it as normal, but have stdout and stderr logged to a file at the same time they're output to the console.

How can I do that on Linux?

another way would be to do: script -a the_logfile #and then run the apps from the 'script' environment, which will log also special characters, ctrl codes, etc, and could be used to "replay" the display if you manage to use it properly, ie watching the log from the same type of terminal and usnig the same lines/columns, and using a "more" or "less" that outputs control chars (ex: more -v the_logfile) — Olivier Dulac, Sep 24, 2013 at 15:28
Is this an application that prints a stream of text, or a full-screen text-mode application? — Gilles 'SO- stop being evil', Sep 24, 2013 at 20:57

Olivier Dulac · Accepted Answer · 2013-09-24 15:27:38Z

11

To pipe only stdout

cmd | tee log.txt | less

To pipe both stdout and stderr:

cmd >>(tee stdout.log) 2>>(tee stderr.log >&2)

Olivier Dulac

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answered Sep 24, 2013 at 9:34

c2h2

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1

Should the > > be >>?
– Supr
Sep 24, 2013 at 13:55
Thanks. Will prefer @goldilocks's answer though because I want both stdout and stderr in the same file, just like I would see them on the console!
– BenMorel
Sep 24, 2013 at 15:37

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Simon M · Accepted Answer · 2013-09-24 13:05:32Z

7

You can use tee. For example:

ls -l / | tee tmp.txt

Will print to stdout, and tmp.txt will contain a copy of the output. If you want to include stderr in tmp.txt:

ls -l / 2>&1 | tee tmp.txt

Simon M

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answered Sep 24, 2013 at 9:35

goldilocks

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Great thanks, just tried it but it looks like it's logging only stdout, is it possible to log stderr as well?
– BenMorel
Sep 24, 2013 at 9:37
@Benjamin That should be cmd 2>&1 | tee .... I edited this in.
– goldilocks
Sep 24, 2013 at 11:58

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Community · Accepted Answer · 2017-03-20 10:18:29Z

There are several ways to do this.

nohup 2>&1 application &. This will send all output to a file called nohup.out. It will also capture SIGHUPs. So you can close the shell and it will keep running. If you wish tyo see what is happening then you can follow the output with tail -f nohop.out.
The tee command will do the same without preventing SIGHUP. C2h and goldilock already mention this.
If you only need limited scrollback, try screen -L. This is explained in more detail in this post.

I realise that screen is a workaround way, but its other features are very nice for deployements.

3 Answers 3