read a specific line from a file

[Bulhac Mihai]

how can i read only a line from a txt file?
for example i want to read only line 3

 

[Pierre-Charles David]

how can i read only a line from a txt file?
for example i want to read only line 3

% cat one_line.rb
#!/usr/bin/env ruby

def read_one_line(file_name, line_number)
File.open(file_name) do |file|
current_line = 1
file.each_line do |line|
return line if line_number == current_line
current_line += 1
end
end
end

puts read_one_line(ARGV[0], ARGV[1].to_i)

% ruby one_line.rb one_line.rb 3
def read_one_line(file_name, line_number)

 

[Peña, Botp]

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ZCByZWdhcmRzIC1ib3RwDQo=

 

[expandafter]

how can i read only a line from a txt file?
for example i want to read only line 3

ruby -e "puts ARGF.to_a[2]" myfile

Another way:

File.open("myfile"){|f|
line = nil
3.times { line = f.gets }
puts line
}

If the whole file will fit in memory,
you can do this:

puts IO.readlines("myfile")[2]

 

[Robert Klemme]

how can i read only a line from a txt file?
for example i want to read only line 3

sed -ne '3 p' your_file

robert

 

[rio4ruby]

From: Bulhac Mihai [mailto:[email protected]]
# how can i read only a line from a txt file?
# for example i want to read only line 3

if you want a ready-made solution (written in ruby, of course), you can use rio.

irb(main):005:0> require 'rio'
=> true

# get first 4 lines (as always in ruby indexing starts at 0)

irb(main):006:0> rio('test.txt').lines[0..3]
=> ["1testing \n", "2testing \n", "3asdfasdf\n", "\n"]

# get first lines 4 to 6

irb(main):007:0> rio('test.txt').lines[3..5] # a range of lines
=> ["\n", "4asdf\n", "[]\n"]

# thus, reading line 3 would be

irb(main):013:0> rio('test.txt').lines[2..2]
=> ["3asdfasdf\n"]

kind regards -botp

Or even
rio('test.txt').line[2]

 

[Robert Klemme]

From: Bulhac Mihai [mailto:[email protected]]
# how can i read only a line from a txt file?
# for example i want to read only line 3

if you want a ready-made solution (written in ruby, of course), you can= use rio.

irb(main):005:0> require 'rio'
=3D> true

# get first 4 lines (as always in ruby indexing starts at 0)

irb(main):006:0> rio('test.txt').lines[0..3]
=3D> ["1testing \n", "2testing \n", "3asdfasdf\n", "\n"]

# get first lines 4 to 6

irb(main):007:0> rio('test.txt').lines[3..5] # a range of lines
=3D> ["\n", "4asdf\n", "[]\n"]

# thus, reading line 3 would be

irb(main):013:0> rio('test.txt').lines[2..2]
=3D> ["3asdfasdf\n"]

kind regards -botp

Or even
rio('test.txt').line[2]

I know a simpler ready made solution:

ruby -ne 'puts $_ if $. =3D=3D 3' your_file

But I'd really prefer the sed solution.

Kind regards

robert

 

[William James]

sed -ne '3 p' your_file

robert

awk "3==NR" your_file

 

[Robert Klemme]

awk "3==NR" your_file

When I think about it, this is probably more efficient for large files
and low line numbers:

head -3 your_file | tail -1



robert

 

[William James]

When I think about it, this is probably more efficient for large files
and low line numbers:

head -3 your_file | tail -1

awk "3==NR{print;exit}" your_file

The rule is: never use anything other than awk unless
you have to.

 

[Robert Klemme]

awk "3==NR{print;exit}" your_file

The rule is: never use anything other than awk unless
you have to.

LOL

robert

 

[James Edward Gray II]

line_three = File.readlines(the_file)[2]

line_three = File.foreach(path) { |line| break line if $. == 3 }

James Edward Gray II

 

[Peña, Botp]

From: rio4ruby [mailto:[email protected]]=20
# Or even
# rio('test.txt').line[2]

thanks. i just wanted (and hoped) that the op will try his hands on rio =
and experiment it.

rio has simple solutions for line grabbing, like eg, "get line 3..5, =
lines 100,200,300..400, and lines containing /test/"

rio('test.txt').line[3..5,100,200,300..400,/test/]

thanks for rio btw=20
-botp

 

[William James]

From: rio4ruby [mailto:[email protected]]
# Or even
# rio('test.txt').line[2]

thanks. i just wanted (and hoped) that the op will try his hands on rio and experiment it.

He ought to learn and experiment with Ruby first.

rio has simple solutions for line grabbing, like eg, "get line 3..5, lines 100,200,300..400, and lines containing /test/"

rio('test.txt').line[3..5,100,200,300..400,/test/]

lines = IO.readlines("phrases_no_extra.txt")
lines.values_at( 3..5,100,200,300..400 ) +
lines.grep( /test/ )

 

[Peña, Botp]

From: William James [mailto:[email protected]]=20
# > rio has simple solutions for line grabbing, like eg, "get=20
# line 3..5, lines 100,200,300..400, and lines containing /test/"
# >
# > rio('test.txt').line[3..5,100,200,300..400,/test/]
#=20
# lines =3D IO.readlines("phrases_no_extra.txt")
# lines.values_at( 3..5,100,200,300..400 ) +
# lines.grep( /test/ )

yap. very clean too, but,=20
1. reads whole file in mem
2. rescans array 2x

kind regards -botp