ed is a line editor for the Unix operating system. It was one of the
first end-user programs hosted on the system and has been standard in
Unix-based systems ever since. ed was originally written in PDP-11/20
assembler by Ken Thompson in 1971.

Navigating

  * Line number: go to that line and print it.
  * pn - Print current line and line number.
  * 3kxe - mark line 3 as "xe".
  * 'xep - print the line marked as xe.

Editing

  * a - start editing after the current line.
  * i - start editing before the current line.
  * c - replace the current line.
  * end the editing with only a period on a line (.).
  * 1d - delete line 1.
  * 1,2j - join line one and two.

Printing

  * 1,$p - print entire buffer.
    * ,p - also prints the entire buffer.
  * 2,3p - print lines 2 and 3.
  * .,4p - print from the current line (.) to line 4.
  * -1,+1p  print 1 line above and 1 line below the current line.

Buffer operations

  * 2t4 - Copy line 2 to after line 4.
  * 2t$ - Copy line 2 to the end of the file.
  * 3m6 - Move line 3 to after line 6.
  * 2,4m$ - Move lines 2 to 4 to the end of the file.

Searching / replace

  * /like - Move to the next line after the current one matching regular expression /like.
  * ?Like - Search backwards.
  * 1s/re/jo - Substitute only the first occurence of re with jo on line 1.
  * 1s/re/jo/g - Substitute all occurences of re with jo on line 1.
  * 1,$s/re/jo/g - Substitute all occurences of re with jo in the whole buffer.

Regular expresions

  * g/re/p - print all the lines matching regular expression /re/.
  * v/re/p - print all the lines NOT matching regular expression /re/.
  * g/re/m$ - move all the lines matching regular expression /re/ to the end of the file.

Reading and writing

  * w file.txt - Save the current buffer as filename file.txt.
  * w - Save the current buffer if the file is already saved.
  * w1,4 - Save lines 1 to 4 to the current buffer.
  * W - append to a file (not replace).
  * r /etc/hosts - Insert the contents of /etc/hosts after the current line.
  * r !ps -e - Insert the output of the command "ps -e" after the current line.
  * e file.txt - Open the file file.txt and replace the current buffer.