System admin

• Note for following commands: it's best practice to enclose all files, directories and variables containing spaces with double quotes, like this:
  find / -name my filename with spaces.txt => find / -name "my filename with spaces.txt"
  

• Linux

  •   Command line / bash

    Note: as usual with *nixes, some commands need to be run as root. If the case, the commands will be preceded by a root prompt : # . A normal user prompt can be $ .

    •     aliases examples

      Put them in the file ~\.bashrc. I start some of my custom aliases with "zz", so typing "zz–TAB" in bash lists them, it's handy.
      

      			
      alias rm='rm -i -v'
      alias cp='cp -i -v'
      alias mv='mv -i -v'
      
      alias ..='cd ..'
      
      alias zznetstat='echo "Useful switches: -n (no dns), -p (process pid/name) or -c (continuous)";echo ;sudo netstat -a -A inet'
      alias zznetstat='echo "Useful switches: -n (no dns), -p (process pid/name) or -c (continuous)";echo ;sudo netstat -tanup'
      alias zz='/home/pi/streams'
      alias zzipt='echo;sudo iptables -nvL'
      alias zzhistsave='history -a'
      alias zzhistload='history -r'
      			

    •     sample commands

      • FIND
        
        Find files (by filename)
        $ find / -name FILENAME
$ find / -name FILENAME 2>/dev/null (without error output)
        
        Find text within files
        

        $ grep -rnw SEARCH_PATH -e "SEARCH_TEXT"
        $ grep -Rnw SEARCH_PATH -e "SEARCH_TEXT" (seems -R better traverses directories)
        $ grep --include=\*.{c,h} -rnw SEARCH_PATH -e "SEARCH_TEXT" (only search for .c and .h files)
        $ grep --exclude=*.o -rnw SEARCH_PATH -e "SEARCH_TEXT" (exclude .o files)
        $ grep --exclude-dir={dir1,dir2,*.dst} -rnw SEARCH_PATH -e "SEARCH_TEXT" (exclude some dirs)

        
        
      • Append one file to another
        $ cat file2 >> file1
        
        
      • Restart networking
        # /etc/init.d/networking restart
        
        
      • IPTABLES
        
        Use a rules files
        # iptables-restore < your_rules_file
        
        Save to a master iptables file
        # iptables-save > /etc/iptables.myconf
        
        Run iptables on boot
        # chmod +x /etc/network/if-pre-up.d/iptables
        
        
        With iptables containing:

        #!/bin/sh
        /sbin/iptables-restore < /etc/iptables.myconf

        Test a rules file
        
        Useful when SSH-ing while changing iptables rules. If anything goes wrong, the old policy will get reloaded.
        # iptables-apply -t 60 your_rules_file
        
        
      • APT
        
        Get the list of installed packages
        $ dpkg --get-selections
        Remove packages that were automatically installed to satisfy dependencies for other packages and are now no longer needed.
        # apt-get autoremove
        Clear out the local repository of retrieved package files.
        # apt-get clean
        Check is a diagnostic tool; it updates the package cache and checks for broken dependencies.
        # apt-get check
        
        
      • Funny stuff
        
        Sometimes, in the console, when you echo a file in binary format (for example cat /etc/localtime[symlink] or cat track.mp3), the console output gets garbled. You can still type and run commands, but some characters are not what they should be !
        This is caused if a character in the binary file is a "SI" character (Shift In; ASCII 14; Control-N). As it's output to the console, it toggles the character set. More info here and here.
        To test this behaviour: type echo  [CTRL]+V [CTRL]+N (there is a space after the echo).This is safer to use than echo-ing a binary file, as the binfile may not have the SI character (check the links if you wanna know what the [CTRL] codes mean).
        The command should look like this in the console: $ echo ^N.
        If typed correctly, root now looks like roo├. Type some words in a text editor (vi tmpfile will be displayed as ┴i ├└p�i┌e) and run some commands. ifconfig if not sure (displayed as i�co┼�i±).
        To revert back to normal mode, type echo  [CTRL]+V [CTRL]+O, which renders $ ec░o ^O.
        

    •     Raspbian specific commands

      See this page for everything about Raspberry Pi.

    •     bash scripting

      This is to put in script files. Files need to be executable ($ chmod +x FILENAME).
      
      
      • Colors and formatting
        
        Escape character is \033 or \e. Some sequences only work on some terminals. More information here.

        NC='\e[0m' # reset all attributes
        
        red='\e[31m'
        green='\e[32m'
        purple='\e[35m'
        cyan='\e[36m'
        yellow='\e[33m'
        orange='\e[38;5;202m'
        
        bold='\e[1m'
        underline='\e[4m'
        dim='\e[2m'
        blink='\e[5m'
        reverse='\e[7m' # invert bg and fg colors
        hidden='\e[8m' # for passwords

        To use them:
        echo -e "Trees have ${green}green leaves" => Trees have green leaves
echo -e "Trees have ${green}green${NC} leaves" => Trees have green leaves
echo -e "Day ${reverse}Night${NC} Day" => Day Night Day
echo -e "Day \e[7mNight\e[0m \e[38;5;202mDay" => Day Night Day
echo -e "\e[32mOnline\e[0m it is" => Online it is
echo -e "\033[32mOnline\e[0m it is" => Online it is
        
        
      • Multiline comments Not really standart, but it's possible (source here).
        Do not use in production, it's just a trick to quickly comment large portions of code.

        : <<'some_string'
        This is an abuse of the null command ":" (colon) and the heredoc syntax
        Do not forget the quotes, it's to make sure no expansion of this text is taking place
        some_string

  •     Vi(m)

    Undo/Redo: u / CTRL+r Display line numbers: :set number. Remove: :set nonumber
    Current line highlight: :set cursorline
    Highlight searches: :set hlsearch. Remove until next search: :nohlsearch or simply :noh. Remove: :set nohlsearch
    
    To copy text, just select it. To paste under cursor, middle-click (sometimes right-click) in INSERT mode.
    Save / Quit / SaveQuit / QuitNoSave: :w :q :wq :q!
    INSERT mode: i
    Delete line: dd
    Delete x lines: dxd or xdd
    Copy line: yy
    Paste current buffer on a new line -after- the current line: p
    Combos deduced from above:
    Swap the current line with the next: ddp
    Cut a line (or x lines) then paste the buffer somewhere: dd (or dxd) to cut, then p to paste.
    Uppercase a letter: gU then left or right arrow (left for previous letter, right for current)
    Lowercase a letter: gu + arrow
    For several letters (with x their number): gUx/gux + arrow (like gU4+arrow to uppercase the next 4 chars, including the current)
    To apply that to a word, replace the arrow by w, so: gUw or guw. Note that it will only apply FROM the position IN the word where the cursor is.
    This works with the whole line, with END, like gu<END> or gU<END>. Same note as above.
    To really do it on a whole line: gUU/gUu or VU / Vu
    Same with a whole word: gUiw or guiw
    Search: /text_to_search. It's a regular expression. Press n for the next item found. To highlight searched text, see above.
    Display lines containing pattern: :g/text_to_search (displaying line numbers is helpful, see above).
    Invert matching selection using :g! or v (g!/text_to_search v/text_to_search).
    Delete lines containing pattern: :g/text_to_search/d.
    Delete blank lines: :g/^\s*$/d
    

  •     Screen

    1. Config (~/.screenrc)
    
    By default, the mouse wheel and the default "SHIFT+PageUp/Down" won't work in screen. Doing so will scroll the normal console output.
    To make it work inside screen -launched from an xterm-, add this to your screenrc:
    # Enable mouse scrolling and scroll bar history scrolling
termcapinfo xterm* ti@:te@
    
    2. Outside of a screen session
    
    List screens: screen -ls
    Create a screen, detach first if necessary then re-attach : screen -d -R $SCREEN_NAME_OR_ID
    Launch a command inside a screen, but don't attach: screen -t $SCREEN_NAME $COMMAND <-- TO CHECK
    
    3. Inside of a screen session
    
    Most commands in screen starts with CTRL+A
    Scroll output: CTRL+a then Escape. Now the nav keys can be used to navigate through the output. Press Enter twice to get back to write mode.
    Detach from a screen (leaving it running): CTRL+a then d (like detach).
    Terminate a screen: CTRL+D
    

• Windows

  •   Command line / batch / etc

    Cmd line redirections: ss64.com | redirections
    
    Concatenate files:
    copy /b partfile.* bigfile.ext
copy /b partfile.1+...+partfile.n bigfile.ext
    Examples:
    copy /b log* all_logs.txt
copy /b *.bat big_script.bat
copy /b file1+log+name2 bigfile.ext