bc-command line calculation

http://www.basicallytech.com/blog/?/archives/23-command-line-calculations-using-bc.html#addition

Expansion

http://linuxcommand.org/lc3_lts0080.php

command substitution:
$(command)
`command`

Arithmetic expansion:
c-style integer expansion: ((expression))
Integer expansion: $[ ] 
bash builtin let command:  let counter="counter + 1"

subprocess expr:  counter=`expr counter + 1'  (must have space around operator)

Quoting:
double quote: all the special characters used by the shell lose their special meaning and are treated as ordinary characters. The exceptions are “$”, “\” (backslash), and “`” (back- quote). This means that word-splitting, pathname expansion, tilde expansion, and brace expansion are suppressed, but parameter expansion, arithmetic expansion, and command substitution are still carried out.

Single quote: suppress all expansions

Signal

Kill: a command used to send signal to a process

signal names can be found by kill -l

SIGTERM (15) least dangerous
SIGKILL (9) 
SIGSTOP (17,19,23)

Regular Expression

a good place to study:  http://www.zytrax.com/tech/web/regex.htm#intro

Bracket, range, negation
[]    indicate a rage, one and only one matching
-     range
^    inside [] means negate the expression

Anchors
^     Beginning
$     Ending
.      Any char at THIS position

Iteration
?           0 or 1
*          0 or more
+          1 or more
{n}       exactly n times  
{n,m}   appears at least n, at most m times
{n,}      at least n times

Other
()     grouping
|      or, alternation

Abbreviations
\d     digit
\D    not digits
\s     space
\S    not space
\b    boundary of words
\B   not boundary
\w   0-9, A-Z, a-z
\W not \w

Vim Configure

http://amix.dk/vim/vimrc.html

Basic

What is shell:
Provide User interface to access Kernel services.
An out layer between user and system kernel.

Need to read:
http://tldp.org/LDP/Bash-Beginners-Guide/html/index.html (I like this one)
http://tldp.org/LDP/abs/html/index.html
https://developer.apple.com/library/mac/DOCUMENTATION/OpenSource/Conceptual/ShellScripting/Introduction/Introduction.html
http://www.gnu.org/software/bash/manual/bashref.html#What-is-Bash_003f
http://www.thegeekstuff.com/tag/bash-tutorial/

Shell types:
sh
bash
csh
tcsh
ksh


Configure profile: (create them if needed)
System wide
/etc/profile
/etc/bashrc

Individual user:
~/.bash_profile
~/.bashrc
~/.bash_login
~/.bash_logout

Variables: Case sensitive, Capital by convention, No Space around equal sign
Global v.s. Local
Types: String, Integer, Constant, Array

Command Substitution: allows the output of a command to replace the command itself

$(command) preferred

`command`

exercise:

http://www.freeos.com/guides/lsst/ch08.html