BASH: How to Redirect Output to File, AND Still Have it on Screen

Fitch · 04-02-2011, 02:17 PM

O.K. I've got the gist of this, but I can't see how to append the output to an existing file. Is that possible?

david1941 · 04-02-2011, 02:43 PM

Append by using the -a option to tee:

Code:

drf@maplepark ~]$ echo 'Output from echo' >archivefile
[drf@maplepark ~]$ echo 'Output from subsequent file run' |tee -a archivefile 
Output from subsequent file run
[drf@maplepark ~]$ cat archivefile 
Output from echo
Output from subsequent file run
[drf@maplepark ~]$

Fitch · 04-03-2011, 02:02 PM

Got it! Thanks Dave

4L3X · 04-21-2011, 04:34 PM

thanks all

I'm now using pretty correctly all this commands/info/redirection

And for what I looked for a long time:
STDOUT + STDERR in a log file + on screen.

Quote:

exec 2>&1
exec > >(tee -a $LOG)

Works like a charm!

MrJoshua · 11-11-2011, 01:15 PM

Nice, works perfectly. I have been searching for quite a while to figure that one out. Never been a big deal so I did not find the time dive deep.

<command> 2>&1 | tee -a logfile

aghabriel · 03-23-2012, 04:34 AM

hi everyone,
i have a question about how could i redirect the output to file renamed by time, for example 20120323.log

we have seen a redirect as "script > file.txt" but the name of this output is always the same "file.txt", we could define a output name with date?

is possible do it? and... how?

catkin · 03-23-2012, 06:04 AM

Quote:

Originally Posted by aghabriel

hi everyone,
i have a question about how could i redirect the output to file renamed by time, for example 20120323.log

we have seen a redirect as "script > file.txt" but the name of this output is always the same "file.txt", we could define a output name with date?

is possible do it? and... how?

Please start a new thread

rahulu123 · 04-06-2012, 07:28 AM

Thank you for much needed information....

Now, what I actually want is to Append the file each time I run a command. I have already tried this but...

Code:

$ ls >> file |tee file

doru · 04-08-2012, 10:22 AM

Quote:

Originally Posted by rahulu123

Thank you for much needed information....

Now, what I actually want is to Append the file each time I run a command. I have already tried this but...

Code:

$ ls >> file |tee file

This is more complicated than it looks at the first glance and you should check man bash to understand better how it works. First, | "assigns" stdout of ls to stdin of tee (see "pipeline" and then "redirection" in man bash). Then, stdout of ls is "assigned" to file (leaving stdin of tee with no input at all), so ls fills file with the list of files. Then, stdout of tee is copied to file, too. Tee receives nothing on its stdin, so it writes an empty file over file before you get any chance to read the file file.

You may want to try:

Code:

ls | tee -a file

if you want to append the list of files to file and to display it on screen at the same time.

If you have nothing better to do, you can also have fun with:

Code:

ls > >(tee -a file)
and: 
tee -a file < <(ls)

rahulu123 · 04-10-2012, 08:00 AM

Quote:

You may want to try:
Code:

Code:

ls | tee -a file

if you want to append the list of files to file and to display it on screen at the same time.

Worked perfectly, Thanks doru

BeachHead · 07-02-2012, 06:12 PM

What if i redirect into a file (ls -l > log.txt) and want it to show in realtime on another console (as if the command would run locally)? 'Cat log.txt' does only show a momentary snapshot. But it should permanently put out new data once appended/logged. An example would be 'tcpdump -i eth0 -n > log.txt'.

Edit: Got it. It's 'tail -f log.txt'