How to use Unix pager programs like `less` from Ruby?

Question

Suppose I have a string called very_long_string whose content I want to send to the standard output. But since the string is very long, I want to use less to display the text on the terminal. When I use

`less #{very_long_string}`

I get File not found error message, and if I use:

`less <<< #{very_long_string}`

I get unexpected redirection error message.

So, how to use less from inside Ruby?

@alex How to do so from inside ruby? But thanks I can try `echo #{long_string}|less`. — Ankit
– Ankit, Commented Mar 9, 2012 at 15:17
@alex And that too doesn't seem to work, I still get file not found error message — Ankit
– Ankit, Commented Mar 9, 2012 at 15:20

user1252434 · Accepted Answer · 2012-03-09 15:23:09Z

19

You could open a pipe and feed your string to less via its stdin.

IO.popen("less", "w") { |f| f.puts very_long_string }

(Assuming very_long_string is the variable holding your string.)

See: http://www.ruby-doc.org/core-1.8.7/IO.html#method-c-popen

answered Mar 9, 2012 at 15:23

user1252434

2,1211 gold badge15 silver badges22 bronze badges

Sign up to request clarification or add additional context in comments.

1 Comment

pedz Over a year ago

There is more to this than meets the eye. Two issues I have: 1) hitting 'q' to quit less produces an EPIPE error that results in a nasty looking stack being dumped out. That's easy to catch wit a rescue. 2) hitting ^C before all the output has been sent to less. less basically just eats the ^C. The ruby code does get an Interrupt but I can't figure out how to gracefully exit and still have less also exit gracefully and set the TTY back to their original settings.

Limbo Peng · Accepted Answer · 2012-03-09 15:41:41Z

1

A simple hack:

require 'tempfile'
f = Tempfile.new('less')
f.write(long_string)

system("less #{f.path}")

answered Mar 9, 2012 at 15:41

Limbo Peng

2,50519 silver badges12 bronze badges

Comments

Community · Accepted Answer · 2017-05-23 11:47:01Z

1

Although less can read text files its natural fit is to use it as the last command in a pipe. So a natural fit would be:

shell-command-1 | shell-command-2 | shell-command-3 | less

At your shell prompt:

echo tanto va la gatta al lardo che ci lascia lo zampino|less

..So you can try this in irb:

`echo tanto va la gatta al lardo che ci lascia lo zampino|less`

but I will prefer to use:

your_string = "tanto va la gatta al lardo che ci lascia lo zampino"
`echo "#{your_string}"|less`

If you have time read this SO question.

For a thorough demonstration of using system calls in ruby see this gist: https://gist.github.com/4069

edited May 23, 2017 at 11:47

CommunityBot

11 silver badge

answered Mar 9, 2012 at 15:24

microspino

7,8113 gold badges52 silver badges51 bronze badges

1 Comment

Ankit Over a year ago

I actually did use it, but nothing happened. No errors, no display nothing. The script simply returned. However, IO.popen() as suggested by @user1252434 worked very well.

Collectives™ on Stack Overflow

How to use Unix pager programs like `less` from Ruby?

3 Answers 3

1 Comment

Comments

1 Comment

Your Answer

Linked

Hot Network Questions

Collectives™ on Stack Overflow

3 Answers 3

1 Comment

Comments

1 Comment

Your Answer

Sign up or log in

Post as a guest

Linked

Related