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What if, when you grep, it goes into pager mode when results don't fit one screen?

sshine profile image Simon Shine ・2 min read

There is a general theme in UNIX commands that if a program is able to deliver ANSI-colored output, it only does so in interactive shells, or if explicitly instructed. If you want to pipe output but have colors remain for later printing, you sometimes have to instruct both the sending and the receiving command.

Of the many alternatives to grep I use ack.

Given the following ~/.ackrc,

--flush
--pager
less -R -F

whenever I ack for something, it uses less as a pager, and if the search results fit a screen, it just prints them, including colors, and otherwise it enters less'es interactive mode.

Here the ack parameters are explained:

  • The parameter --flush tells ack to "flush output immediately. This is off by default unless ack is running interactively (when output goes to a pipe or file)." So with --flush, output is always sent immediately.

  • The parameter --pager tells ack to pipe its output through less -R -F. This is equivalent to always running ack ... | less -R -F when typing ack ....

Here the less parameters are explained:

  • -R (--RAW-CONTROL-CHARS) prints ANSI color escape sequences. That means colored output and not a bunch of ESC[1;39m codes.
  • -F (--quit-if-one-screen) "causes less to automatically exit if the entire file can be displayed on the first screen."

The one drawback I have experienced so far is that if you do a very slow ack with very few results that don't take up a lot of screen space, you won't get those results until ack has finished or it eventually uses an entire screen, since then it knows to activate the pager rather than print directly.

You can circumvent this last quirk with less -X (--no-init) which "disables sending the termcap initialization and deinitialization strings to the terminal," but it means that less will not wipe its output from the terminal when you hit q.

Decide which drawback you like less, or let me know of third options!

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sshine profile

Simon Shine

@sshine

I like purely functional programming.

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