tokenization & Command identification process added

Author: ArnobKumarSaha

how-bash-process/readme.md

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+Bash executes a 5-step process before execute a command.
+
+## 1) Tokenization :
+
+After Tokenization the whole command divides into parts. Each of the part is either 'word' or 'operator'.
+
+### Word doesn't contain any unquoted meta-character
+### Operator containes at least one  unquoted meta-character
+
+So here, the meaning of unquoted meta-character plays the vital role to distiguish between words & operators.
+
+In linux, There are total of 10 punctuations that are known as metaCharacters. They are :: <br>
+ | & ; ( ) < > space tab newLine
+
+We also need to know the meaning of 'unquoted' too.  There are 3 types of quoting (means Removing special meaning) in linux.  They are :: <br>
+
+i)   \  -> Removing special meaning of next character <br>
+ii)  '' -> Removing special meaning of all the characters inside <br>
+iii) "" -> Removing special meaning of all the characters inside, except dollar($) and backtick(`).
+
+So In simple, If you find any of the 10 metaCharacters, that has not been quoted in any of the above three ways, Thats an operator !!
+
+
+## 2) Command Identification :
+
+There are two types of commands. Simple & Compound.  To distinguish between them, We need a good understanding of operators. As we already know what actually operators are, lets divide them into different types :
+
+a) Control operators : <br>
+| || & && ; ;; ;& ;;& |& ( ) newLine
+
+b) Redirection operators : <br>
+< > << >> <& >& <> <<- >|
+
+Look carefully that, redirection operators always either < or >. Also, space and tab are just separators. They dont have effect on controlling or redirecting.
+
+## 3) Expansion :
+
+As this stage is a very big and complex, it generally divided into 4 steps.
+### a) Brace Expansion :
+It will be easier to understand this by example, rather than explanation.
+
+echo {a,b,42,arnob}_xyz # prints a_xyz b_xyz 42_xyz arnob_xyz <br>
+echo {1..5} # prints 1 2 3 4 5  <br>
+echo {z..a..5} # prints z u p k f a <br>
+mkdir -p path/{ucb/{ex,edit},lib/{ext,abc}}  # make directories .. <br>path/lib/abc , path/lib/ext ,  path/ucb/edit , path/ucb/ex
+
+### b) Intermidiate Expansion :
+
+### c) Word splitting :
+
+### d) Globbing :
+
+
+
+
+## 4) Quote Removal :
+
+## 5) Redirection :