The abstract of (chapter01 to chapter03)

Chapter 1. Why shell programming?
The chapter answer why you need to grasp shell programming and answer when not to use shell scripts.

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Chapter 2. Starting off with a sha-bang
Start a file with #! /XXX/xxx and make it executable.
#! /Bin/sh
#! /Bin/bash
#! /Usr/bin/perl
#! /Usr/bin/TCL
#! /Bin/sed-F
#! /Usr/awk-F

2.1. Invoking the script
1 make the script executable.
Chmod 555 scriptname
Chmod + RX scriptname
Chmod U + RX scriptname
2 execute the shell script
./Criptname arguments

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Chapter 3. Exit and exit status
1 $? Reads the exit status of the Last Command executed. $? Is especially useful for testing the result of a command in a script.
Caution:
Certain exit status codes have reverved meanings and shoshould not be user-specified in a script.

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Chapter 4. special characters
1 Comments :#
Eg: # This line is a comment.
But the first Hash (#) In the next statement is not a comment.
Echo $ {path # * :}# parameter substitution, not a comment.
Caution:
Certain pattern matching operations also use #.
2 command separator :;
Eg: Echo hello; echo there
3 terminator in a case option:; [double semicolon]
Eg: Case "$ variable" in
ABC) echo "$ variable = ABC ";;
XYZ) echo "$ variable = xyz ";;
Esac
3 dot command :.
1st: A dot is equivalent to source. This is a bash builtin.
2nd: In a regular expression, a dot matches a single character.
3rd: A dot is the filename prefilx of a "hidden" file, a file that an ls will not normally show.
4 patial quoting: "[double quote]
5 full quoting: '[single quote]
6 comma OPERATOR :,
7 ESCAP:/x
8 Filename Path separator :/
9 command substitution :'
10 NULL command ::
11 reverse (or negate) the sense of a test or exit status :!
12 wild card :*
13 wild card (single character ):?
14 variable substitution: $
Caution:
In a regular expression, a $ matches the end of a line.
15 parameter substitution :$ {}
16 positional parameters: $ *, $ @
17 Command Group :()
Eg: (A = Hello; echo $)
18 brace expansion :{}
Eg: grep Linux File *. {txt, HTM *}
# In the files "filea.txt", "file2.txt", "filer.html", "file-87.htm", etc.
18: block of code :{}
Eg: Bash $ {local A; A = 123}
19 test: []
Test expression between []. Note that [is part of the shell builtin test, not a link to the external command/usr/bin/test.
20 test: [[]
Test expression between [[] (shell keyword ).
21 integer expansion :(())
Expand and evaluate integer expression (()).
22 redirection: >>>>> <
23 pipe: |
24 Force redirection:> 1
25 run job in Background :&
26 redirection from/to stdin or stdout:-[dash]
27 previous working directory:-[dash]
28 minus :-
29 equals: =
30 plus: +
31 modulo: %
32 Home Directory :~
33 current working directory :~ +
34 previous working directory :~ -
35 control characters
CTL-C: terminate a foreground job.
CTL-D: log out from a shell (simial to exit or EOF)
Ctl-6: "BEL" (beep)
CTL-H: backspace
CTL-J: Carriage Return
CTL-M: newline
CTL-u: erase a line of input
CTL-Z: Pause a foreground
36 whitespace: functions as a separator, separating command or variables.
Note: $ ifs, the special variable separating fields of input to certain commands, defaults to whitespace.