Shell Basics

bashBasics.sh

foo=bar 
" The value is '$foo'" # prints The value is bar

foo=$(pwd)
" We are in '$foo' " # prints We are in < PATH >

cat <(ls) <(ls ..) # concats the output of ls and ls ..

mkdir sandbox / # Will need permissions
sudo !! # !! inserts mkdir sandbox /

ls & # runs in the background
; 	# executes the next command
true || echo "Hello World" # will always print "Hello World"
true && echo "Hello"  # will always print "Hello"
false && echo "World" # will never print "World"

$_ # returns the last argument
$? # returns if last command was successful
$0 # the current command running
$# # the number of arguments
$$ # the process id
$@ # all the arguments 

echo "Starting program at $(date) "
echo "Running program $0 with $# arguments with pid $$"

for file in "$@"; do
	grep foobar "$file" > /dev/null 2> dev/null
	# When pattern is not found, grep has exit status 1
	# We redirect STDOUT and STDERR to a null register since we do not care
	
	if [[ "$?" -ne 0 ]]; then
		echo "File $file does not have any foobar, adding one"
		echo "# foobar" >> "$file"
	fi
done