Bash Notes

- : enable the option
+ : disable the option
Example:
  set -o errexit
  equals to
  set -e

Control operators:
   & && ( ) \n ;; ; | ||
Redirection operators:
   < > << >> <> <& >& <<- >|

Single Quotes: preserve the literal meaning of all the chars except '
Double Quotes: preserve the literal meaning of all the chars except $ ` \
Backslash: preserve the literal meaning of all the chars except \n

Reserved Words:
   ! { } case do done elif else esac fi for if then until while

Aliases:

Commands:
Simple Commands Order:
   Leading words name=value; Word Expansions; Redirection

Redirections:
  [n]> file
  [n]>| file
  [n]>> file
  [n]< file
  [n]<> file
  [n]<&n2
  [n1]<&-
  [n1]>&n2
  [n]>&-

Search and Execution:
   shell functions,
   built-in commands,
   normal programs

Path Search for normal programs:
   shell function, built-in, then PATH

Command Exit Status:
   zero succeed
   non-zero failure
   128+signo  terminated by a signal

Complex Commands:
   simple command
   pipeline
   list or compound-list
   compound command
   function definition

Pipelines:
   [!] command1 [| command2 ...]

Background Commands:
   command1 & [command2 & ...]

Lists:

Short-Circuit List Operators:
   && ||

Flow-Control Constructs:
   if list
   then list
   else iist
   fi

   while list
   do list
   done

   for variable [in word ...]
   do list
   fone

   break [num]
   continue [num]

   case word in
   pattern) list ;;
   ...
   esac

Grouping Commands Together:
  (list)
or
  { list; }

Functions
  name ( ) command
  local variable
  return [exit status]

Variables and Parameters:
  name=value

Positional Parameters:
  $0 $1 ...


Special Parameters:
  $*: positional parameters starting from one
  $@: positional parameters starting from one
  $#: number of positional parameters
  $?: the exit status of the most recent pipeline
  $-: the current option flags
  $$: the process id of the invoked shell
  $!: the process ID of the most recent background command
  $0: name of the shell or shell script

Word Expansions:
  Tilde Expansion, Parameter Expansion, Command Substitution,
  Arithmetic Expansion, Quote removal

Tilde Expansion:
   ~/.tools/list
   /usr/name/.tool/list

Parameter Expansion:
   ${expression}

   ${parameter:-word} : Use default value
   ${parameter:=word} : Assign default value
   ${parameter:?[word]} :Indicate Error if Null or Unset
   ${parameter:+word} : Use Alternate Value

   ${#parameter} : string length
   ${parameter%word} : Remove smallest suffix pattern
   ${parameter%%word} : Remove largest suffix pattern
   ${parameter#word} : Remove smallest prefix pattern
   ${parameter##word} : Remove largest prefix pattern

Command Substitution:
   $(command)  or
   `command`

Arithmetic Expansion:
   $((expression))

While Space Splitting:

Pathname Expansion:

Shell Patterns:
   ! * ? [
   *: any string of chars
   ?: any single char
   [: introduce a char class
   ]: end a char of class

Built-in Commands:
: null cmmand that return a 0 exit value
. file:  file is read and excuted
[ : built-in equivalent of test
alias [name[=string] ...] :
bg [job ...': background
builtin cmd: execute the specified built0in command
bind:
cd  directory:
chdir:
command [-p]
command [-v]
echo  [-e | -n] [string ...]
eval string ...
exec [command [arg ...]]
exit [exitstatus]
export name ...
export [-p]
false
fc [-e editor]
fc -l
fc -s
fg [job]
getopts optstring var
hash [-rv] [command ...]
jobid [job]
jobs [-lps]
local:
pwd [-L | -P]
read [-p prompt] [-t timeout] [-er] variable
readonly [-p] [name]
return [exitstatus]
set [-/+abCE..]
setvar variable value
shift [n]
test
times:
trap [action] signal
trap -l
true
type [name ...]
unlimit
unmask
unalias
unset
wait [job]