UNIX

File Commands

• mkdir - Make a directory (-p for nested/file/structure)
• touch - Create a file
• cp - Copy (-r for recursive, -i to prompt for overwrites)
• cmp - Compare files
• diff - See difference between files. (-i for case-insentive, -B for ignore blanks, -w for ignore whitespace)
  • < - File 1
  • > - File 2
  • d - Delete
  • a - Add
  • c - Change
• sdiff - Advanced diff. (-s to ignore matches)
  • nothing - Identical
  • < - File 1
  • > - File 2
  • | - Different
• dircmp - Compare directories
• ls - List (-a to include hidden files, -l for long form, -R for recursive)
• mv - Move or rename (-i for interactive)
• rmdir - Remove directorys (can take multiple)
• find <directory> "<search string>"
  • -print (display results)
  • -exec compress {} \; (compress the file when you find it)
  • -ok rm {} \; (delete the file when you find it)
• mtime -4 - (limit results to files modified in the last 4 days)
• locate <filename> - find system files
• ln <first file> <second file> - Hard link two files together. (-s for soft link, plus dirs)
  • Hard links are identical, soft links are dependent
• file <file_name> - Display file metadata
• split -b 500M big_file.jpg - Splits into 500MB chunks
  • Use cat to recombine
• sort file_1 file_2 > destination_file - Sort by first character of each line
  • -t, +1 (comma delimited, sort on second field)
  • -u to eliminate duplicates
• uniq <file_name> - Removes duplicate lines
• tr a-zA-Z A-Za-z < <file_name> - Translate file
• fmt <file_name> -w 60 - Format file to a 60 character line
• wc = word count - -w for words, -l for lines, -c for bytes). Can pipe from ls.

Shell Commands

• less - Paging (scroll up and down with arrow keys)
• more - Paging (spacebar, b [if no pipes], q to quit)
• | - Pipe output to input
• > - Redirect output to something other than screen
• >> - Append to output
• tee - Sends output to multiple locations
  • | tee <first_output> | <second_output>
• chsh - Change shell
• tab - Autocomplete, twice for options
  • up, down to search
• ctrl + a - Beginning of a line, ctrl + e = end of a line
• stty, stty sane, reset - Fix weird remote issues
• exit - Quit shell
• alias - Show a list of aliases
• alias <new>=<old> - Set a shortcut for the session only
• ; - Separate commands on the same line
• && - Same as ;, but only runs if the first one succeeds
• history <number> - Show lines of history
• env - Print your environment variables
• <variable_name>=<value> - Sets a shell variable
• export <variable_name> - Makes a shell variable an environment variable
• export <variable_name>=<value> - Set an environment variable
• echo $<variable_name> - Show a variable
• alt+. - Pull up the final argument of the last command. Keep pressing for previous commands. Useful when you have to do several things to the same file. Requires this in vi-mode: bindkey "\e." insert-last-word.

Prompts

• $PS1 - Regular prompt
• $PS2 - Secondary prompt
• %n - Current user
• %~ - Current directory with path
• %c - Current directory without path
• %t - Time
• %w - Date, no year
• %W - Date with year
• \n - Force new line
• %m - Hostname
• %M - Hostname with domain

Search Commands

• cat - Display, can take multiple files, can redirect into another file
• tac - Reverse cat
• head/tail -20 - File start or end of file. Can do multiple files.
• tail -f - "follow" updates
• grep <needle regex> <haystack> - search. (-5 for context lines, -c for count, -v for all lines that don't match, -i for case-insensitive)
• ctrl+r - Reverse search through history

awk/sed

• sed 's/old/new/gim' <source_file> > <destination_file> - Search & replace
  • Can save seds as scripts
  • g = global, i = case-insensitive, m = multiline
• awk -F, /search/{ <command> $1 } <file_name> - Work with delimited files
  • -F sets delimiter, $1 is the first field
  • Can save awks as scripts

Shells

• What shells do you have available? cat /etc/shells
• sh has no completion or aliasing
• csh allows you to script in C
• bash/ksh/zsh allows a blend of features and simple scripting
• Temporarily jump into a shell by executing it
• zsh autocompletion while cycle through options while tabbing

Tips

• Multiple commands can be separated with ;
  • && is the same as ;, but only runs if the first one succeeds
• Find out what shell you’re using with echo $SHELL
• * is a general wildcard, ? is a single-character wildcard
• History is in ~/.bash_history - good for stubbing out scripts
• ^cd^ls runs last command, swapping out cd for ls
• nano : pico :: vim : vi
• Find out what group you’re in with grep username /etc/passwd
• Find out general group info with more /etc/group
• A t at the end of a permissions list is a "sticky bit", and means it can only be modified by its owner
• You own any files that you cp
• Shell variables are tied to the shell, environment variables exist for any shell
• zsh config is in /etc/zprofile, /etc/zshenv, /etc/zsh/zshrc.
• User overrides are in ~/.zprofile, ~/.zshrc
• Edit the PATH= in .zshrc to add more default paths
• alias <new>=<old> - Set a shortcut. Goes in .zshrc file.