Shell Commands - kimschles/schlesinger-knowledge GitHub Wiki

• Create a file using echo and text redirection >

echo 'Hello World!' > say_hello.txt

• Append lines to a file using echo and text redirection >>

echo 'How are you?' >> say_hello.txt

• Use cat to look at the contents of one or more files

cat file1.txt file2.txt

• Look at the last part of one or more files with tail

tail file1.txt file2.txt

• Look at the last part of a file while it is being written

tail -f file1.txt

• Count the number of words in one or more files with word count!

wc -w file1.txt

• Count the number of lines in one or more files

wc -l file1.txt

• Count the number of characters in one or more files

wc -m file1.txt

• Count the number of bytes in one or more files

wc -c file1.txt

• See all the information in one or more files

wc file1.txt

• Look at your options (and add more!) for your shell

sudo nano /etc/shells

• Change your default shell

chsh -s <path to your default shell>

• Encode to base64

echo -n 'kim schlesinger was here' | base64

• result: a2ltIHNjaGxlc2luZ2VyIHdhcyBoZXJl

• Decode

echo -n 'a2ltIHNjaGxlc2luZ2VyIHdhcyBoZXJl' | base64 -D

• result: kim schlesinger was here

• note: use -d for anything other than OSX

• See the route tables on your machine

netstat -rn

• SSH into an ubuntu server on port 2222 ssh -i <key> ubuntu@<address> -p 2222 -vvvv

• add read permissions to all users (owner/user, group, others) chmod a+r

• read only chmod 400

• turn a group of commands into a single command that ssh can consume bash -c

• Send a lot of requests to a url ab -n 30000 -c 100 http://<external_ip_here

• This sends 30,000 requests, 100 at a time

• Name server lookup nslookup <domain.com>

• Copy something from your cli to your mac clipboard pbcopy echo $PWD | pbcopy

• list what is in a directory and their attributes

  • ls

• list what is in the directory, and show directory ownership, permissions and sizes

  • - means it is a file
  • d means it is a directory
    • ls -l

• show sizes in a human-readable format

  • ls -lh

• show all files and directories, including hidden ones

  • ls -a

• sort files by size with the biggest one at the top

  • ls -S

• list directories recursively

  • ls -R

• sort files by the last time they were modified

  • ls -t

Note: these flags can be combined. For example, ls -lt

• whoami

  • shows the username of the user that is currently logged in
  • it displayes the $LOGNAME variable

• substitute user command: su

  • su <user_name>
  • su - will change you to the root user

• Reboot a linux system

  • reboot

• Shutdown a linux system

  • halt or poweroff

• Show your top running processes

  • top

Let's you see information about your kernel

• Show the name of the kernel

  • uname

• See the kernel's release number

  • uname -r

• Build version

  • uname -v

• Machine type

  • uname -m

• Operating System

  • uname -o
  • echo $OSTYPE

• All the info uname can show

  • uname -a

• domain information groper (perform DNS lookups)

  • dig NS <domain_here>

• You command history is stored in .bash_history
• $HISTFILESIZE sets how many commands to keep in your history
• $HISTCONTROL allows you to modify the behavior of your bash history
  • For example, ignoredups ignores duplicate commands
• history prints out your command history
• If you want to run a command again:
  • !<history_number> runs that command again

The order files are executed during login:

1. The first file that is called during a login shell is /etc/profile

• system-wide and startup scripts

1. Next, the system looks for the following files and runs the first one it finds:

• ~/.bashprofile
  • sets user specific shell envs
• ~/.bash_login
• ~/.profile

1. Next, ~/.bashrc

• non-login functions and aliases

1. Then, /etc/bashrc

• system-wide functions and aliases

Logout

1. .bash_logout

• $PWD
• $OLDPWD
• Create a variable in your current shell:
  • NAME=Kim
• Create a global variable that is accessible from any shell:
  • export NAME=Kim
• Look at all your variables
  • env
• Look at your variables in alphabetical order (this doesn't work on a mac)
  • set

• Use this when you don't know the exact name or location of a file
• * is the wildcard.
  • ls *.txt searches the directory for all .txt files
  • ls test* searches for all files that have the word test
• ? matches one character; ???? matches four characters
  • ls ????.txt searches for a text file with a name that is four characters in length
  • ls test?.txt seaches for a text file with test and one additional character
• [xyz] matches any one of the characters in the list
  • ls [Ss]*.sh looks for files that have an s in their name
  • Find a file regarding test scores: ls [tT]est[Ss]cores20[0-9]*
• [^abc] matches everything execpt these characters
• [0-9] matches this range of numbers
  • 201[0-8]

• Double quotes " " allow $VARIABLES be evaluated
  • "My username is $USER"
  • The variable is evaluated like echo
• Single quotes ' ' ensure the string is evaluated literally. No special behavior for $
• \ disables special character functionality right after the \

• kschlesinger@Kims-MacBook-Air:~ *user@computer-name:current-directory

• locate searches a local database of files and folders
• find searches the file system. Use this syntax:
  • find /path/to/directory -name file
• whereis shows you the location of the binary and man pages (if available)

• man <command_name> pulls up the manual page for that command

  • man pages are all formatted the same way

    The standard sections of the manual include:
    
    1      User Commands
    2      System Calls
    3      C Library Functions
    4      Devices and Special Files
    5      File Formats and Conventions
    6      Games et. al.
    7      Miscellanea
    8      System Administration tools and Daemons
    
    Distributions customize the manual section to their specifics,
    which often include additional sections.``` 
    
    

• whatis <search_term> lists man pages related to the search term

  • man -f <search_term> does the same thing

• apropos <search_term> searches the whatis database for the search term

  • shows a list of man pages that contain the search term man -k <search_term> does the same thing

• reset

  • Reset your terminal window.

• kubectl get pods | grep -v 3d

  • Exclude 3d from the search

• Change into root user

  • sudo -i

• Search for an executable (the example is openvpn)

  • sudo find / -type f -name "openvpn"

• Find your IP address from the command line:

  • curl ifconfig.co

  Standard Output and Error

  • Standard Output, stdout, is the default. When in the command line, it is when thing are printed to the console
  • It is common to redirect to Standard Error, stderr. 2>
    • Example: ls 2> e
  • To send output to both stout and stderr use 2>&1