shell

You may know about ctrl+shift+R for reverse case-insensitive search (or whatever it stands for) and that is still useful if you remember one very unique keyword from the middle of a command.

bash script compare text

if [ $var == "value" ]
then
echo is the same
fi

http://www.tech-recipes.com/rx/209/bournebash-shell-scripts-string-comparison/

(Numbers are -eq)

bash script check for existence of any argument

if [ $# -ne 1 ]
then
echo "USAGE: scriptname arg1 arg2"
return
fi

concatenate all files in directory (GNU-Linux)

cat ls -rt > newfilename

Note the backticks.