cheat sheets.

$ command line ruby cheat sheets
!! - Last command
  !foo - Run most recent command starting with 'foo...' (ex. !ps, !mysqladmin)
  !foo:p - Print command that !foo would run, and add it as the latest to command history
  !$ - Last 'word' of last command ('/path/to/file' in the command 'ls -lAFh /path/to/file', '-uroot' in 'mysql -uroot')
  !$:p - Print word that !$ would substitute
  !* - All but first word of last command ('-lAFh /path/to/file' in the command 'ls -lAFh /path/to/file', '-uroot' in 'mysql -uroot')
  !*:p - Print words that !* would substitute

  ^foo^bar - Replace 'foo' in last command with 'bar', print the result, then run. ('mysqladmni -uroot', run '^ni^in', results in 'mysqladmin -uroot')

  {a,b,c} passes words to the command, substituting a, b, and c sequentially (`cp file{,.bk}` runs `cp file file.bk`)

  Ctrl + a - Jump to the start of the line
  Ctrl + b - Move back a char
  Ctrl + c - Terminate the command
  Ctrl + d - Delete from under the cursor
  Ctrl + e - Jump to the end of the line
  Ctrl + f - Move forward a char
  Ctrl + k - Delete to EOL
  Ctrl + l - Clear the screen
  Ctrl + r - Search the history backwards
  Ctrl + R - Search the history backwards with multi occurrence
  Ctrl + t - Transpose the current char with the previous
  Ctrl + u - Delete backward from cursor
  Ctrl + w - Delete backward a word
  Ctrl + xx - Move between EOL and current cursor position
  Ctrl + x @ - Show possible hostname completions
  Ctrl + z - Suspend/ Stop the command
  Ctrl + x; Ctrl + e - Edit line into your favorite editor

  Alt + < - Move to the first line in the history
  Alt + > - Move to the last line in the history
  Alt + ? - Show current completion list
  Alt + * - Insert all possible completions
  Alt + / - Attempt to complete filename
  Alt + . - Yank last argument to previous command
  Alt + b - Move backward
  Alt + c - Capitalize the word
  Alt + d - Delete word
  Alt + f - Move forward
  Alt + l - Make word lowercase
  Alt + n - Search the history forwards non-incremental
  Alt + p - Search the history backwards non-incremental
  Alt + r - Recall command
  Alt + t - Transpose the current word with the previous
  Alt + u - Make word uppercase
  Alt + back-space - Delete backward from cursor

  (Here "2T" means Press TAB twice)
  $ 2T - All available commands(common)
  $ (string)2T - All available commands starting with (string)
  $ /2T - Entire directory structure including Hidden one
  $ (dir)2T - Only Sub Dirs inside (dir) including Hidden one
  $ *2T - Only Sub Dirs inside without Hidden one 
  $ ~2T - All Present Users on system from "/etc/passwd"
  $ $2T - All Sys variables
  $ @2T - Entries from "/etc/hosts"
  $ =2T - Output like ls or dir
  .bash_profile = sourced by login shell, 
  .bashrc = sourced by all shells, 
  .bash_aliases = should be sourced by .bashrc

Run something:
  for i in a b c; do $i 'hello'; done

Do something on a bunch of files:
  for i in *.rb; do echo "$i"; done

If syntax:
  if [[ -e .ssh ]]; then echo "hi"; fi

Numerical comparison:
  i=0; if (( i <= 1 )); then echo "smaller or equal"; else echo "bigger"; fi

file check flags:
  -e:  file exists
  -f:  regular file (non directory)
  -d:  directory
  -s:  non-zero file
  -x:  execute permission

Avoid duplicates in your history:
  export HISTIGNORE="&:ls:ls *:[bf]g:exit"

more here: