Monthly Archives: February 2016

use tee to send output to STDOUT and a pipe

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Generally, tee is used to send output from a command to both STDOUT and to a file. You can also use tee to send output to STDOUT and pass the output on to another command like you would normally using a pipe. This uses a process substitution syntax.

~$ echo "some error message" | tee >(logger -t test_error_msg)
some error message
~$ grep test_error_msg /var/log/syslog
Feb 24 11:37:54 foohost test_error_msg: some error message
~$

The error message is output to STDOUT and also sent to the logger command (which writes it to syslog). This can be usefull when you have silent cron jobs (>/dev/null 2>&1) that log errors to syslog, but at the same time if you run the shell script by hand you can see the error output.

start screen session with 4-way split screen

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There are several terminals that allow splitting the screen to accommodate multiple regions in a single window. When logged into a non-desktop/server environment Linux screen is great for this. It has support for splitting the screen vertically and/or horizontally. You can use ctrl + a + S or ctrl + a + | to split regions horizontally or vertically. Here’s an excerpt from a .screenrc file to split the screen into 4 regions, and start ssh sessions to four separate servers in each of those regions.


split
split -v
focus down
split -v

screen -t bash /bin/bash
screen -t deploy1 /usr/bin/ssh deploy1
screen -t deploy2 /usr/bin/ssh deploy2
screen -t deploy3 /usr/bin/ssh deploy3
screen -t deploy4 /usr/bin/ssh deploy4

focus up
focus left
select 1
focus right
select 2
focus left
focus down
select 3
focus right
select 4

Now I can start the screen session…

# screen -c .screenrc-multiwindow

and automatically get this:

4-way-screen-split