Politics, Robotics and Linux: Vim Visual Selection Tricks



# VISUAL SELECTION TRICKS:
  # You can use filters and vim's execution mode.to do some powerful things.
  # A filter is any standard UNIX program (sort, awk, grep, cut, paste, sed ...) that can read from stdin and write to stdout.
  # Vim's execution mode lets you read in or replace text with the output of a program. If you make a visual selection (say,
  # using V or C-V), and hit :, your command prompt will immediately be :'<,'>, which means "Apply whatever command follows
  # to the lines included in the visual selection." At this point, you can write !foo to replace the text with the output of
  # program foo.

  # For example, to sort the text by the python column, select it, hit :, and enter !sort -k5. The whole command will look like
    :'<,'>!sort -k5
  # Running it will produce:

       a  b  cd  1  p
       b  b  cd  2  y
       c  b  cd  3  t
       d  b  cd  4  h

  # Results in:

       d  b  cd  4  h
       a  b  cd  1  p
       c  b  cd  3  t
       b  b  cd  2  y

  # For more complex tasks, awk is your friend. A command like
    :'<,'>!awk '{ print $1, $3, $2, $4, $5 }'

a cd b 1 p
b cd b 2 y
c cd b 3 t
d cd b 4 h

  # will flip the second and third columns (but note that inter-column spacing is collapsed).
  # To do maths on a column, try something like
    :'<,'>!awk '{ sub($4, $4*2+1); print }'

       a  b  cd  3  p
       b  b  cd  5  y
       c  b  cd  7  t
       d  b  cd  9  h

  # Could get the same result with perl if there is only one column of numbers:
    :'<,'>!perl -pe 's/\d+/$&*2+1/e'

  # To flip the visual selection just select the rows and then:
    :'<,'>!tac

       d  b  cd  4  h
       c  b  cd  3  t
       b  b  cd  2  y
       a  b  cd  1  p

  # This pipes the lines through the unix 'reverse cat' program.