I love aliases. There are many useful shortcuts, e.g. ".." as an alias for "cd ..". If I got shell access to a system, I first install my version of vimrc, bashrc, bash_alias, and so on. I keep those files in a subversion repository, so I can synchronize them.
Some commands only work when required programs are installed or if a special directory exists. Most of the times, this is not a problem: if the program is not installed, the alias simply does not work. But what, if you want to install "colormake" as "make". Okay, this seems to be a bad idea, but I think, you understand the point 
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A workaround would be to test weather a desired program is installed before installing an alias. This worked nicely. Until I got access to a Router and a very slow PC: the login needed 5 seconds. I decided to write a simple DSL, which creates my bash_alias based on a series of checks. The resulting file is than static. Here is the first part of the script:
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#!/bin/sh
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debug=0
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#######
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skip=1
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supported=1
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debug() {
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[ $debug -ne 0 ] && echo $* >&2
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}
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while read -r line; do
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debug -n "\"$line\" -> "
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if [ $skip -eq 0 ]; then
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if [ "${line#::#}" != "$line" ]; then
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debug "comment skipped"
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elif [ "${line#::}" != "$line" ]; then
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debug -n "control command: "
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case $line in
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::c)
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supported=1
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debug "supported cleared"
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;;
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::e:*)
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cmd=${line#::e:}
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if [ "$supported" -eq 0 ]; then
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debug "section already skipped"
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else
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which $cmd >/dev/null 2>&1
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if [ $? -eq 0 ]; then
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debug "file exists" >&2
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else
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supported=0
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debug "file does not exist. section skipped."
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fi
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fi
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;;
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::p:*)
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cmd=${line#::p:}
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if [ $supported -eq 0 ]; then
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debug "section already skipped"
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else
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perl -e "eval 'use $cmd'; exit (length \$@ == 0 ? 0 : 1);" >/dev/null 2>&1
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if [ $? -eq 0 ]; then
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debug "perl module exists"
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else
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supported=0
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debug "perl module does not exist. section skipped."
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fi
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fi
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;;
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::d:*)
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cmd=${line#::d:}
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if [ $supported -eq 0 ]; then
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debug "section already skipped"
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else
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if [ -d "$cmd" ]; then
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debug "directory exists"
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else
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supported=0
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debug "directory does not exist. section skipped."
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fi
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fi
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;;
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::r:*)
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cmd=${line#::r:}
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if [ $supported -eq 0 ]; then
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debug "section already skipped"
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else
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if [ -r "$cmd" ]; then
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debug "readable"
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else
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supported=0
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debug "not readable. section skipped."
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fi
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fi
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;;
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::n)
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debug "inverting skip status"
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if [ $supported -eq 0]; then
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supported=1
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else
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supported=0
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fi
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;;
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*)
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echo "unsupported control command: $line" >&2
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esac
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else
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if [ $supported -eq 1 ]; then
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/bin/echo "$line"
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debug "supported"
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else
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debug "not supported"
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fi
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fi
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else
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if [ "$line" = "###END###" ]; then
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skip=0
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debug "skippping disabled"
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else
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debug "skipped"
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fi
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fi
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done < $0
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exit 0
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###END###
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#!/bin/bash
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#WARNING - THIS FILE IS GENERATED AUTOMATICALLY
The file opens itself, seeks "###END###" and processes everything after it. It defines several commands:
- ::e:myfile - skip lines until next ::c if myfile does not exist
- ::d:mydir - skip lines until next ::c if directory mydir does not exist
- ::r:myfile - skip lines until next ::c if file myfile is not readable
- ::n - inverts skipping state (imagine this as "else)
- ::p:module - skip lines until next ::c if the perl module module is not installed
- ::c - clear skip state
This is freaky to read, but simple to use and it can be easily extended. Note the explicit call of /bin/echo in line 97. This was the only way I found to get this script working witch both dash and bash (their "echo" words differently if they find a backslash).
Okay, last but not least some examples for the second part (most parts are collected from several websites):
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alias ..='cd ..'
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alias ...='cd ../..'
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alias 2..='cd ../..'
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alias 3..='cd ../../..'
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alias 4..='cd ../../../..'
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alias 5..='cd ../../../../..'
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alias path='echo -e ${PATH//:/\\n}'
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alias ls='ls $LS_OPTIONS'
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alias l='ls $LS_OPTIONS -l'
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alias ll='ls $LS_OPTIONS -lA'
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alias lg='ls | grep -i'
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alias llg='ll |grep -i'
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alias grep='grep --color=auto'
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alias rm='rm -i'
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alias cp='cp -i'
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alias mv='mv -i'
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alias p='ps aux'
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alias psg='ps aux | grep'
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::e:tree
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alias tree='tree -Csu'
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::c
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::e:screen
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# starts screen in the background
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alias bgscreen='screen -d -m'
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::c
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::e:ccze
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alias c='ccze -m ansi'
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::e:less
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alias lless='c |less -NiR' # cat ... | lless
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::c
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::e:colordiff
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alias diff=colordiff
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::c
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::p:Smart::Comments
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alias cperl="perl -MSmart::Comments"
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::c
To create a customized bash_aliases just run shomething like "sh mkalias.sh > ~/.bash_aliases".