introduction
shell
	interface available on any UNIX-like OS
	interesting: both UI and API
shell input [XCU 2.1]
	specified file
	'-c' option argument
	stdin (interactive mode)
first steps: `echo` command [XCU 4]
ex. 1: Hello world
	demonstration of input methods
	ex. 1.1:
		[sh]
			$ echo Hello world
	ex. 1.2:
		[hello.sh]
			echo Hello world
		[sh]
			$ sh hello.sh
	ex. 1.3:
		[sh]
			$ sh -c 'echo Hello world'
magic number behavior, `chmod` [XCU 4], file modes
ex. 2: magic hello
	[hello-magic.sh]
		#! /bin/sh
		echo Hello world
	[sh]
		$ chmod a+x
		$ sh hello-magic.sh
field splitting [XCU 2.6.5]
simple commands: `cd`, `ls`, `mkdir`, `touch` [XCU 4]
ex. 3: field splitting
	[sh]
		$ mkdir foo bar
		$ ls
tilde expansion [XCU 2.6.1]
ex. 4: tilde expansion
	[sh]
		$ ls ~
		$ ls ~sh-foo
		$ ls ~sh-foo/some-directory
pathname expansion [XCU 2.6.6] [XCU 2.13]
ex. 5: pathname expansion
	[sh]
		$ echo ~sh-foo/*-file
		$ echo ~sh-foo/ba*/file
parameters: assignment
ex. 6: parameter assignment
	[sh]
		$ myparam=foo
		$ mynum=1
parameters: expansion [XCU 2.6.2]
	simple parameter
	use default values
	string length
	remove {smallest,largest} suffix pattern
	remove {smallest,largest} prefix pattern
ex. 7: parameter expansion
	[sh]
		$ echo ${myparam}
		$ echo ${nullparam:-default}
		$ echo ${#myparam}
		$ file=main.c
		$ echo ${file%.c}.o
		$ dir=foo/bar/baz
		$ echo ${dir##*/}
positional parameters [XCU 2.5.1]
ex. 8: positional parameters
	[pos-params.sh]
		#! /bin/sh
		echo ${1}
		echo ${2}
	[sh]
		$ chmod a+x pos-params.sh
		$ sh pos-params.sh foo
		$ ./pos-params.sh foo bar baz
special parameters [XCU 2.5.2]
	@, *, #, ?, 0
exit status [XCU 2.8.2]
`false` and `true` commands [XCU 4]
ex. 9: special parameters
	[spec-params.sh]
		#! /bin/sh
		echo Number of positional parameters: ${#}
		echo Positional parameters: ${@}
		echo Script name: ${0}
		true
		echo ${?}
		false
		echo ${?}
	[sh]
		$ chmod a+x spec-params.sh
		./spec-params.sh foo bar baz
shell variables [XCU 2.5.3]
	HOME, IFS, PATH, PS1, PWD
ex. 10: shell variables
	[sh]
		$ echo ${HOME}
		$ echo ${PWD}
	[sh (another shell)]
		$ PS1='$ '
		$ PS1='PROMPT> '
command substitution [XCU 2.6.3]
	two versions
ex. 11: command substitution
	[sh]
		$ filepath=$(basename ~sh-foo/bar/file)
		$ echo ${filepath}
arithmetic expansion [XCU 2.6.4]
ex. 12: arithmetic expansion
	$ echo $((2+3))
	$ echo $((0x10 + 4))
	$ i=0
	$ i=$(($x + 1))
	$ echo ${i}
basic foundation complete
simple commands revisited [XCU 2.9.1]
	simple-command: [parameter-assignment...] [word...]
	command search and execution
pipelines [XCU 2.9.2]
lists [XCU 2.9.3]
	AND-OR list
	list
ex. 13: lists
	[sh]
		$ false && echo foo || echo bar
		$ true || echo foo && echo bar
compound commands [XCU 2.9.4]
	grouping
	if, `test` command
	while
	until
	for
	case
functions [XCU 2.9.5]
I/O redirection [XCU 2.7]