#!/bin/sh
# First line of the script is shebang which tells the system how to execute
# the script: http://en.wikipedia.org/wiki/Shebang_(Unix)
# As you already figured, comments start with #. Shebang is also a comment.

# Simple hello world example:
echo Hello, world!

# Each command starts on a new line, or after semicolon:
echo 'This is the first line'; echo 'This is the second line'

# Declaring a variable looks like this:
VARIABLE="Some string"

# But not like this:
VARIABLE = "Some string"
# Bash will decide that VARIABLE is a command it must execute and give an error
# because it couldn't be found.

# Using the variable:
echo $VARIABLE
echo "$VARIABLE"
# When you use the variable itself — assign it, export it, or else — you write
# its name without $. If you want to use variable's value, you should use $.

# Reading a value from input:
echo "What's your name?"
read NAME # Note that we didn't need to declare new variable
echo Hello, $NAME!

# We have the usual if structure:
if true
then
    echo "This is expected"
else
    echo "And this is not"
fi

# Expressions are denoted with the following format:
echo $(( 10 + 5 ))

# Unlike other programming languages, bash is a shell — so it works in a context
# of current directory. You can list files and directories in the current
# directories with ls command:
ls

# These commands have options that control their execution:
ls -l # Lists every file and directory on a separate line

# Results of the previous command can be passed to the next command as input.
# grep command filters the input with provided patterns. That's how we can list
# txt files in the current directory:
ls -l | grep "\.txt"

# Commands can be substitued within other commands using $( ):
# The following command displays the number of files and directories in the
# current directory.
echo "There are $(ls | wc -l) items here."

# Bash uses a case statement that works similarily to switch in Java and C++:
case "$VARIABLE" in 
    #List patterns for the conditions you want to meet
    0) echo "There is a zero.";;
    1) echo "There is a one.";;
    *) echo "It is not null.";;
esac

#For loops iterate for as many arguments given:
#The contents of var $VARIABLE is printed three times.
for $VARIABLE in x y z
do
    echo "$VARIABLE"
done