# Shell Tips and Tricks

This is a simple list of tips and tricks for the shell that I discovered over the course of many years of messing around in shell and wanted to coalesce into a single document, partly to remember, and partly to share with others.

## Persistent SSH Sessions

In order to ensure that your SSH sessions do not get disconnected after a period of inactivity simply add the following to your .ssh/config file:

Host *
ServerAliveInterval 300
ServerAliveCountMax 2


Now your SSH session will persist, and not be killed by an overzealous firewall.

## Mogrify with GNU Parallel

Having recently needed to convert a large quantity of images to another format I stumbled upon GNU parallel, a powerful and simple utility for executing shell jobs in parallel.

Here is a simple example where I use GNU parallel to parallelize the conversion of a series of svs (a format commonly used for pathology images from digital whole slide scanners) to tiff, a much more common format for scientific images. Simply prepend parallel to your command, and GNU parallel will execute the command with the line as arguments. The triple colon indicates that the list of svs files in the directory are being passed into GNU parallel where they can be chunked out into jobs across the ten specified concurrent processes.

# Using 10 cores instead the default of all possible cores
parallel mogrify -j10 -verbose -format tif ::: *.svs

##### Peter Lawson
###### NSF Fellow and PhD Candidate in Bioinnovation

My current research involves applying topological data analysis to gain insights into topological differences in cancer morphology at the histological level and their importance in diagnosis and prognosis.