Put the following into ~/.bash_profile:

# Do not clean the screen when man exits. Search case-insensitively.

# Read the man page of man to know what environment variable to set.

# It's either PAGER or MANPAGER.

export PAGER="/usr/bin/less -iRsX"

# Or you may change the global option for less, assuming man uses less by default:

export LESS="-iRsX"

# Make Bash append rather than overwrite the history on disk:

shopt -s histappend

# Whenever displaying the prompt, write the previous line to disk:

PROMPT_COMMAND='history -a'

# Colorful grep, see http://www.debian-administration.org/articles/460

# 'always' is more dangerous than 'auto', 'coz it sends control characters all the way down the pipe (if any)

export GREP_OPTIONS='--color=always'

# Use vim as a syntax-highlighting pager, see ":help less"