TheShell

ls
cd
# relative paths .. . ~
date
man
[command] --help # help informations
cat
sort [file] # to sort the lines in file in Lexicographical order
echo
rm
rmdir
mkdir
touch
tail -n[num] [filename]
head -n[num] [filename]
grep [mode] [filename]
sed
pwd # present working directory

echo Hello world # prints "Hello world" as two arguments
echo Hello    world # same output
echo "Hello world" # prints "Hello world"
echo Hello\ world # Uses an escape character to send "Hello world" as an argument
echo "Jon's computer" # prints "Jon's computer"
echo 'Jon's computer'' # prints "Jon" and then "s computer"
echo Jon\'s\ computer # prints "Jon's computer"

grep -r [string] [directory]
sed [many comlicated usage]
find [path] -type [type_argument] -mtime +[days] -name [filename]

a.* # a, ab, abc, apple or something
^a # starts with a
. # Any letter
<letter>* # letter 0 times or more
ab+c # abc, abbc, abbbc... but not ac
colou?r # colour or color, u for 0 times or once
[abc] # a or b or c, like a, b, c
[a-z] # all little letters
[A-Z] # all capital letters
[0-9] # all numbers
[^abc] # not a, b or c
[a-zA-Z0-9] # letters or numbers
\d # for [0-9]
\d\d # for 10-99
\D # for not numbers
\s # for blanks