bash

Append contents of all matching files to sum.log

cat *.log >> sum.log

Overwrite sum.log with contents of all matching files

cat *.log > sum.log

Get full path of a file (file does not need to exist)

readlink -f file.txt

Repeat a command n times

for run in {1..10}; do command; done

Convert timestamp to human readable date

date -d @641288145

Shorten prompt in current terminal

PS1='\u:\W\$ '