search in Emacs [ word under the cursor]

C-s C-w , appends the rest of the word under the cursor to the search pattern.

\[ or $$ instead of displaymath

You can use \[ math formula \] or $$math formula$$ instead of
\begin{displaymath}
math formula
\end{display math}

this is particularlty useful if you dont want to write small formula and don't want to break the paragraph to type it.

Redirections in Bash

command > filename 2>&1
directs both standard output and standard error to the file filename

command 2>&1 > filename
directs only the standard output to file, filename because the standard error was duplicated as standard output before the standard output was redirected

setting page ranges while printing

`lp` allows you to give the page ranges to print ,

-P page-list
Specifies which pages to print in the document. The list can contain a list of numbers and ranges (#-#) separated by commas (e.g. 1,3-5,16).