File Commands
ls – directory listing
ls -a – directory listing with hidden files
ls -al – formatted directory listing with hidden files
cd dir – change directory to dir
cd – change to home
cd – – change back to previous directory
pwd – show current directory
mkdir dir – create a directory dir
rm file – delete file
rmdir dir – delete empty directory dir
rm -r dir – recursively delete directory dir (use with caution)
rm -f file – force remove file; no error output if file doesn’t exist
rm -rf dir – recursively force remove directory dir (use with caution)
cp file1 file2 – copy file1 to file2
cp file1 file2 file3 dir – copy file1, file2 and file3 to dir
cp -r dir1 dir2 – recursively copy dir1 to dir2; create dir2 if it doesn’t exist
mv file1 file2 – move file1 to file2 if file2 is an existing directory, moves file1 into directory file2
ln -s file link – create symbolic link link to file
>file – create file (use with caution, doing this on an existing file will overwrite the content)
touch file – create or update file
cat > file – places standard input into file
cat file1 > file2 – overwrites the content of file2 with the content of file1
cat file1 >> file2 – appends the content of file1 to file2
echo „Hello World“ > file – overwrites file’s content with Hellow World
echo „Hello World“ >> file – appends Hello World to the end of file
less file – output the contents of file
more file – output the contents of file
head file – output the first 10 lines of file
tail file – output the last 10 lines of file
tail -f file – output the contents of file as it grows, starting with the last 10 lines
sed ‘s/foo/bar/g’ file – replaces all occurrences of foo with bar in file
sed -i.backup ‘s/foo/bar/g’ file – replaces all occurrences of foo with bar in file after backing up file as file.backup
rm {m,M}yfile – remove files according to a pattern
Example:
$ ls
$ touch myfile Myfile myfile1 Myfile1
$ ls
myfile Myfile myfile1 Myfile1
$ rm {m,M}yfile
$ ls
myfile1 Myfile1

Process Management
ps – display your currently active processes
top – display all running processes
kill pid – kill process id pid
killall proc – kill all processes named proc * file
bg – lists stopped or background jobs; resume a stopped job in the background
fg – brings the most recent job to foreground
fg n – brings job n to the foreground

File Permissions
chmod octal file – change the permissions of file to octal, which can be found separately for user, group, and world by adding:

• 4 – read (r)
• 2 – write (w)
• 1 – execute (x)

Examples:
chmod 777 – rwx for all
chmod 755 – rwx for owner, rx for group and world. For more options, see man chmod

SSH
ssh user@host – connect to host as user
ssh -p port user@host – connect to host on port port as user
ssh-copy-id user@host – add your key to host for user to enable a keyed or password-less login

Searching
grep pattern files – search for pattern in files
grep -r pattern dir – search recursively for pattern in dir
command | grep pattern – search for pattern in the output of command
updatedb – updates the slocate database; see next item
locate file – find all instances of file; may need to run updatedb first
find $HOME -user root – find files owned by root in $HOME
find /path -depth -type d -empty – find empty directories
find /path -type d -empty -exec rm -rf ‘{}’ \; – find and delete empty directories
find /path -depth -type f -empty – find empty files
find /path -name [name_of_file] – find a file with a specific name
find /path -name „*.[given_extension]“ – find a file with a specific extension
find /path -name ‘*.txt’ -perm 644 – find .txt files with specific permissions
find /path -perm -[permission_bits] – find files with some given permissions
find /path -name ‘[given_name].*’ – find files with a given name and any extension
man -t man | ps2pdf – > man.pdf – make a pdf of a man page

System Info
date – show the current date and time
cal – show this month’s calendar
uptime – show current uptime
w – display who is online
whoami – who you are logged in as
finger user – display information about user
uname -a – show kernel information
cat /proc/cpuinfo – cpu information
cat /proc/meminfo – memory information
man command – show the manual for command
df – show disk usage
du – show directory space usage
free – show memory and swap usage
whereis app – show possible locations of app
which app – show which app will be run by default
lshw -html > hardware.html – create an overview of hardware
lsb_release -a – show information about the distro
tr : ‘\n’ <<<$PATH – show directories in the PATH, one per line
sed ‘s/:/\n/g’ <<<$PATH – show directories in the PATH, one per line with sed

Compression
tar cf file.tar files – create a tar named file.tar containing files
tar xf file.tar – extract the files from file.tar
tar cf file.tar.gz files – create a tar with Gzip compression
tar xf file.tar.gz – extract a tar using Gzip
tar cf file.tar.bz2 – create a tar with Bzip2 compression
tar xf file.tar.bz2 – extract a tar using Bzip2
gzip file – compresses file and renames it to file.gz
gzip -d file.gz – decompresses file.gz back to file

Network
ping host – ping host and output results
whois domain – get whois information for domain
dig domain – get DNS information for domain
dig -x host – reverse lookup host
wget file – download file
wget -c file – continue a stopped download

Installation
Install from source:
./configure – execute the configure script
make – compile the source
make install – install needed files
dpkg -i pkg.deb – install a deb package on .deb-based systems
rpm -Uvh pkg.rpm – install an rpm package on .rpm-based systems

Shortcuts
Ctrl+A – move to the start of the line
Ctrl+E – move to the end of the line.
Ctrl+U – delete from the cursor to the beginning of the line.
Ctrl+K – delete from the cursor to the end of the line.
Ctrl+W – delete from the cursor to the start of the word.
Ctrl+Y – pastes text from the clipboard.
Ctrl+L – clear the screen leaving the current line at the top of the screen.
Ctrl+C – halts the current command
Ctrl+Z – stops the current command, resume with fg in the foreground or bg in the background
Ctrl+D – log out of current session, similar to exit
Ctrl+R – reverse search
^abc^xyz – replace first occurrence of abc with xyz in last command and execute it
!! – repeats the last command
sudo !! – repeats the last command with sudo privileges
exit – log out of current session

Find за линукс ни позволява да му подадем различни аргументи включително и да изпълнява различни команди на всеки открит файл. Това много лесно може да се използва find да ни върне имената на файлове по-стари от X дни и имената на тези файлове да бъдат предадени към   rm който да ги изтрие.

Синтаксис на командата

find /path/to/files* -mtime +5 -exec rm {} \;

Забелжка има шпация между rm, {}, и \;

Обяснение

• Първият аргумент е пътят до файловете.
• Вторият аргумент е -mtime той се използва за да се укаже колко стари файлове да изтрием. Например ако укажем +mtime +5 ще изтрием файловете по-стари от 5 дни.
• Третият аргумент -exec ни позволява да предадем резултата от еърната команда към rm който да изтрие файловете
• Краят {} \; е задължителен за завършване на командата