myos.md

Utopia OS

Shell

Command

# command
name [args ...] [Redirection]

# pipeline
[!] command [| command]

# list
pipeline [[<newline> or ; or & or && or ||] pipeline]

Redirection	Description
[fd]<file	redirect fd to file, default fd is 0 (stdin)
[fd]<<EOF	redirect fd to the content from next line to the line contaion EOF, default fd is 0 (stdin)
[fd]<<<string	redirect fd to string, default fd is 0 (stdin)
[fd]>file	redirect fd to file, truncate the file if it is exist or else create it first, default fd is 1 (stdout)
[fd]>>file	redirect fd to file, append to the file if it is exist or else create it first, default fd is 1 (stdout)
fd1>&fd2	redirect fd1 to fd2

Expansion

1. Brace Expansion

   Before	After
   {a,b,c}	a b c
   {a..c}	a b c
   {1..3}	1 2 3
   {1..3..2}	1 3
   {01..9}	01 02 03

2. Tilde Expansion

   Before	After
   ~	/home/current_user
   ~user	/home/user

3. Parameter Expansion

   Before	After
   ${parameter}	parameter value
   ${!parameter}	indirect parameter value
   ${#parameter}	length of parameter value
   ${parameter:-word}	use default value
   ${parameter:=word}	assign default value
   ${parameter:?word}	display error if null or unset
   ${parameter:+word}	use alternate value
   ${!prefix*}	names matching prefix (string)
   ${!prefix@}	names matching prefix (table)
   ${!prefix[*]}	list of table keys (string)
   ${!prefix[@]}	list of table keys (table)

4. Command Substitution

   Before	After
   $(command)	the stdout of command

5. Arithmetic Expansion

   Before	After
   $((expression))	the result of arithmetic expression

6. Process Substitution

   Before	After
   <(list)	the name of a input FIFO file under /dev/fd where the stdout of list redirects to
   >(list)	the name of a output FIFO file under /dev/fd where the stdin of list redirects to

7. Word Splitting

8. Pathname Expansion

   Before	After
   *	all files and directories
   **	all files, directories and subdirectories
   ?	matches any single character
   []	same as [] in regular expression

9. Quote Removal

   • ' ': all expansion are disabled
   • " ": only parameter expansion, command substitution and arithmetic expansion are enabled
   • \: escape character

Parameter

• data types: string and table
• scopes: local, global and environment

let name=value       # local scope
let -g name=value    # global scope
let -e name=value    # env scope
unlet name
unlet -g name
unlet -e name

# string
string
'string with single quote'
"string with double quote"
# table
(0 1 2)
([0]=0 [1]=1 [2]=2)
([zero]=0 [one]=1 [two]=2)

# expand to the value of variable name in local scope, global scope or env scope
# "${table[@]}" == "0" "1" "2"
# "${table[*]}" == "0 1 2"
$name ${name}

Special Parameters	Description
$0	executable name
$1 $2 $3 ...	positional arguments
$@	all positional arguments (table)
$*	all positional arguments (string)
$#	count of positional arguments
$$	pid of current shell
$?	exit status of the most recently executed foreground pipeline

Control Flow

if list; then
  list;
elseif list; then
  list;
else
  list;
end

switch word in
  case pattern[|pattern2]
    list;
end

while list; do
  list;
end

for name in word ... do
  list;
end

Function

function name()
  list;
end

Kernel

File System

• /
  • boot/
  • usr/
  • bin/
  • lib/
  • etc/
  • var/
  • run/
  • proc/
  • sys/
  • dev/
  • mnt/
  • tmp/
  • home/
    • username/
      • Downloads/
      • Desktop/
      • Douments/
      • Pictures/
      • Videos/
      • Musics/
      • .config/
      • .cache/
      • .local/share/

---

• fs features
  • copy-on-write
  • dedup
  • snapshots
  • compression
  • encryption

---

• file state
  • path
  • size
  • blocks
  • links
  • type
    • regular file
    • directory
    • symbol link
    • fifo
    • socket
    • character
    • block
    • ...
  • uid
  • access
    • regular file
      • read
      • write
      • execute
    • directory
      • read
      • add
      • change
      • delete