Shell Input
-----------

    sh@sleipnir1:~$ vim hello.sh
    sh@sleipnir1:~$ cat hello.sh
    echo Hello world
    sh@sleipnir1:~$ sh hello.sh
    Hello world
    sh@sleipnir1:~$ sh -c 'echo Hello world'
    Hello world
    sh@sleipnir1:~$ echo Hello world
    Hello world

Comments, Magic Number Behavior, and File Modes
-----------------------------------------------

    sh@sleipnir1:~$ vim hello.sh
    sh@sleipnir1:~$ cat hello.sh
    #! /bin/sh
    # This is a comment
    echo Hello world
    sh@sleipnir1:~$ ./hello.sh
    -su: ./hello.sh: Permission denied
    sh@sleipnir1:~$ ls -l hello.sh
    -rw-r--r-- 1 sh sh 48 Mar 30 13:26 hello.sh
    sh@sleipnir1:~$ chmod a+x hello.sh
    sh@sleipnir1:~$ ls -l hello.sh
    -rwxr-xr-x 1 sh sh 48 Mar 30 13:26 hello.sh
    sh@sleipnir1:~$ ./hello.sh
    Hello world

Field Splitting and Quoting
---------------------------

    sh@sleipnir1:~$ mkdir foo bar
    sh@sleipnir1:~$ ls
    bar  foo  hello.sh
    sh@sleipnir1:~$ rmdir foo bar
    sh@sleipnir1:~$ mkdir foo\ bar
    sh@sleipnir1:~$ ls
    foo bar  hello.sh
    sh@sleipnir1:~$ rmdir foo\ bar
    sh@sleipnir1:~$ ls
    hello.sh
    sh@sleipnir1:~$ mkdir 'foo bar
    > baz'
    sh@sleipnir1:~$ ls
    foo bar?baz  hello.sh
    sh@sleipnir1:~$ rmdir 'foo bar
    > baz'
    sh@sleipnir1:~$ ls
    hello.sh
    sh@sleipnir1:~$ mkdir "foo bar baz"
    sh@sleipnir1:~$ ls
    foo bar baz  hello.sh

Tilde Expansion
---------------

    sh@sleipnir1:~$ echo ~
    /home/sh
    sh@sleipnir1:~$ ls ~sh-foo
    another-directory  another-file  bar  baz  foo  some-directory  some-file
    sh@sleipnir1:~$ ls ~sh-foo/some-directory
    Hey, this is a cool file!

Pathname Expansion
------------------

    sh@sleipnir1:~$ echo ~sh-foo/*-file
    /home/sh-foo/another-file /home/sh-foo/some-file
    sh@sleipnir1:~$ echo ~sh-foo/ba*/file
    /home/sh-foo/bar/file /home/sh-foo/baz/file
    sh@sleipnir1:~$ echo ~sh-foo/ba[a-r]/file
    /home/sh-foo/bar/file
    sh@sleipnir1:~$ echo ~sh-foo/ba[p-z]/file
    /home/sh-foo/bar/file /home/sh-foo/baz/file

Parameter Assignment
--------------------

    sh@sleipnir1:~$ myparam=foo
    sh@sleipnir1:~$ mynum=1

Parameter Expansion
-------------------

    sh@sleipnir1:~$ echo ${myparam}
    foo
    sh@sleipnir1:~$ echo ${nullparam:-default}
    default
    sh@sleipnir1:~$ echo ${#myparam}
    3
    sh@sleipnir1:~$ file=main.c
    sh@sleipnir1:~$ echo ${file%.c}.o
    main.o
    sh@sleipnir1:~$ dir=foo/bar/baz
    sh@sleipnir1:~$ echo ${dir##*/}
    baz

Positional Parameters
---------------------

    sh@sleipnir1:~$ vim pos-params.sh
    sh@sleipnir1:~$ cat pos-params.sh
    #! /bin/sh
    echo ${1}
    echo ${2}
    sh@sleipnir1:~$ chmod a+x pos-params.sh
    sh@sleipnir1:~$ ./pos-params.sh foo
    foo
    
    sh@sleipnir1:~$ sh pos-params.sh foo bar baz
    foo
    bar

Special Parameters
------------------

    sh@sleipnir1:~$ vim spec-params.sh
    sh@sleipnir1:~$ cat spec-params.sh
    #! /bin/sh
    
    echo Number of positional parameters: ${#}
    echo Positional parameters: ${@}
    echo Script name: ${0}
    sh@sleipnir1:~$ sh spec-params.sh foo bar baz
    Number of positional parameters: 3
    Positional parameters: foo bar baz
    Script name: spec-params.sh

Exit Statuses
-------------

    sh@sleipnir1:~$ vim spec-params.sh
    sh@sleipnir1:~$ cat spec-params.sh
    #! /bin/sh
    
    echo Number of positional parameters: ${#}
    echo Positional parameters: ${@}
    echo Script name: ${0}
    true
    echo ${?}
    false
    echo ${?}
    sh@sleipnir1:~$ sh spec-params.sh foo bar baz
    Number of positional parameters: 3
    Positional parameters: foo bar baz
    Script name: spec-params.sh
    0
    1

Shell Variables and Links `.` and `..`
--------------------------------------

    sh@sleipnir1:~$ echo ${HOME}
    /home/sh
    sh@sleipnir1:~$ echo ${PWD}
    /home/sh
    sh@sleipnir1:~$ ls
    foo bar baz  hello.sh  pos-params.sh  spec-params.sh
    sh@sleipnir1:~$ cd foo\ bar\ baz/
    sh@sleipnir1:~/foo bar baz$ echo ${PWD}
    /home/sh/foo bar baz
    sh@sleipnir1:~/foo bar baz$ ls .
    sh@sleipnir1:~/foo bar baz$ mkdir file1 file2
    sh@sleipnir1:~/foo bar baz$ ls .
    file1  file2
    sh@sleipnir1:~/foo bar baz$ ls ..
    foo bar baz  hello.sh  pos-params.sh  spec-params.sh
    sh@sleipnir1:~/foo bar baz$ cd ..
    sh@sleipnir1:~$ echo ${PWD}
    /home/sh
    sh@sleipnir1:~$ PS1='$ '
    $ PS1='PROMPT> '
    PROMPT> echo Hello
    Hello
    PROMPT> PS1='$ '
    $ echo Hello \
    > World
    Hello World

Command Substitution
--------------------

    $ filepath=$(basename ~sh-foo/bar/file)
    $ echo ${filepath}
    file

Arithmetic Expansion
--------------------

    $ echo $((2+3))
    5
    $ echo $((0x10 + 4))
    20
    $ i=0
    $ i=$(($i + 1))
    $ echo ${i}
    1
    $ i=$(($i + 1))
    $ echo ${i}
    2
    $ i=$(($i + 1))
    $ echo ${i}
    3

Simple Commands
---------------

    $ i=0 echo Hello
    Hello

Command Search and Execution
----------------------------

    $ echo ${PATH}
    /usr/local/bin:/usr/bin:/bin:/usr/local/games:/usr/games
    $ ./hello.sh
    Hello world
    $ hello.sh
    -su: hello.sh: command not found
    $ ls
    foo bar baz  hello.sh  pos-params.sh  spec-params.sh
    $ PATH=${PATH}:${HOME}
    $ echo ${PATH}
    /usr/local/bin:/usr/bin:/bin:/usr/local/games:/usr/games:/home/sh
    $ hello.sh
    Hello world

Pipelines
---------

    $ ! true
    $ echo ${?}
    1
    $ ! false
    $ echo ${?}
    0
    $ true
    $ echo ${?}
    0
    $ false
    $ echo ${?}
    1

Lists
-----

    $ false && echo foo || echo bar
    bar
    $ true || echo foo && echo bar
    bar

`test` Command and `if` Construct
---------------------------------

    $ [ foo = foo ] && echo equal || echo not equal
    equal
    $ if [ foo = foo ]; then echo equal else echo not equal; fi
    equal else echo not equal
    $ if [ foo = foo ]; then echo equal; else echo not equal; fi
    equal
    $ if [ foo = foo ]; then
    >     echo equal
    > else
    >     echo not equal
    > fi
    equal

`while` Loop
------------

    $ i=0
    $ while [ ${i} -lt 5 ]; do
    >     echo ${i}
    >     i=$(($i + 1))
    > done
    0
    1
    2
    3
    4
    $ vim param-loop.sh
    $ cat param-loop.sh
    while [ ${#} -gt 0 ]; do
        echo Parameter: ${1}
        shift
    done
    $ sh param-loop.sh foo bar baz
    Parameter: foo
    Parameter: bar
    Parameter: baz

`for` Loop
----------

    $ for param in foo bar baz; do
    >     echo ${param}
    > done
    foo
    bar
    baz

`case` Construct
----------------

    $ param=foo
    $ case ${param} in
    >     f*)
    >         echo starts with f
    >         ;;
    >     b*)
    >         echo starts with b
    >         ;;
    > esac
    starts with f

Functions
---------

    $ print_hello()
    > {
    >     echo Hello world
    > }
    $ print_hello
    Hello world
    $ print_params()
    > {
    >     echo ${@}
    > }
    $ print_params 1 2 3
    1 2 3

Input/Output Redirection
------------------------

    $ echo Hello world > hello-file
    $ cat hello-file
    Hello world
    $ echo Hello world > hello-file
    $ echo Hello world > hello-file
    $ echo Hello world > hello-file
    $ cat hello-file
    Hello world
    $ echo Hello world >> hello-file
    $ echo Hello world >> hello-file
    $ cat hello-file
    Hello world
    Hello world
    Hello world
    $ vim read-file.sh
    $ cat read-file.sh
    while read line; do
        echo Line: ${line}
    done < myfile.txt
    $ sh read-file.sh
    Line: line one
    Line: line two
    Line: some other line
    $ vim read-file.sh
    $ cat read-file.sh
    while read field1 field2; do
        echo Line: ${field1}, ${field2}
    done < myfile.txt
    $ sh read-file.sh
    Line: line, one
    Line: line, two
    Line: some, other line
    $ echo Hello world > /dev/null
    $ sh -c not-a-command
    sh: 1: not-a-command: not found
    $ sh -c not-a-command 2> /dev/null
    $ while read line; do
    >     echo Line: ${line}
    > done <<EOF
    > this is input
    > some more input
    > EOF
    Line: this is input
    Line: some more input