Best practices with STDIN in Ruby

Question

I want to deal with the command line input in Ruby    gt  cat input txt   myprog rb  gt  myprog rb  lt  input txt  gt  myprog rb arg1 arg2 arg3       What is the best way to do it  In particular I want to deal with blank STDIN  and I hope for an elegant solution      usr bin env ruby  STDIN read split   n   each do  a     puts a end  ARGV each do  b      puts b end

User · Answer

Ruby provides another way to handle STDIN  The -n flag  It treats your entire program as being inside a loop over STDIN   including files passed as command line args   See e g  the following 1-line script      usr bin env ruby -n   example rb  puts  hello          prepend  hello   to each line from STDIN   these will all work      example rb  lt  input txt   cat input txt     example rb     example rb input txt

User · Answer

Something like this perhaps     usr bin env ruby  if  stdin tty    ARGV each do  file      puts  do something with this file    file     end else    stdin each line do  line      puts  do something with this line    line     end end   Example    gt  cat input txt     myprog rb do something with this line  this do something with this line  is do something with this line  a do something with this line  test  gt    myprog rb  lt  input txt  do something with this line  this do something with this line  is do something with this line  a do something with this line  test  gt    myprog rb arg1 arg2 arg3 do something with this file  arg1 do something with this file  arg2 do something with this file  arg3

User · Answer

Something like this perhaps     usr bin env ruby  if  stdin tty    ARGV each do  file      puts  do something with this file    file     end else    stdin each line do  line      puts  do something with this line    line     end end   Example    gt  cat input txt     myprog rb do something with this line  this do something with this line  is do something with this line  a do something with this line  test  gt    myprog rb  lt  input txt  do something with this line  this do something with this line  is do something with this line  a do something with this line  test  gt    myprog rb arg1 arg2 arg3 do something with this file  arg1 do something with this file  arg2 do something with this file  arg3

User · Answer

Quick and simple   STDIN gets chomp     YES

User · Answer

I am not quite sure what you need  but I would use something like this      usr bin env ruby  until ARGV empty  do   puts  From arguments    ARGV shift   end  while a   gets   puts  From stdin    a   end   Note that because ARGV array is empty before first gets  Ruby won t try to interpret argument as text file from which to read  behaviour inherited from Perl    If stdin is empty or there is no arguments  nothing is printed   Few test cases     cat input txt     myprog rb From stdin  line 1 From stdin  line 2      myprog rb arg1 arg2 arg3 From arguments  arg1 From arguments  arg2 From arguments  arg3 hi  From stdin  hi

User · Answer

I am not quite sure what you need  but I would use something like this      usr bin env ruby  until ARGV empty  do   puts  From arguments    ARGV shift   end  while a   gets   puts  From stdin    a   end   Note that because ARGV array is empty before first gets  Ruby won t try to interpret argument as text file from which to read  behaviour inherited from Perl    If stdin is empty or there is no arguments  nothing is printed   Few test cases     cat input txt     myprog rb From stdin  line 1 From stdin  line 2      myprog rb arg1 arg2 arg3 From arguments  arg1 From arguments  arg2 From arguments  arg3 hi  From stdin  hi

User · Answer

I do something like this     all lines      ARGV each do  line    all lines  lt  lt  line     n  end puts all lines

User · Answer

I am not quite sure what you need  but I would use something like this      usr bin env ruby  until ARGV empty  do   puts  From arguments    ARGV shift   end  while a   gets   puts  From stdin    a   end   Note that because ARGV array is empty before first gets  Ruby won t try to interpret argument as text file from which to read  behaviour inherited from Perl    If stdin is empty or there is no arguments  nothing is printed   Few test cases     cat input txt     myprog rb From stdin  line 1 From stdin  line 2      myprog rb arg1 arg2 arg3 From arguments  arg1 From arguments  arg2 From arguments  arg3 hi  From stdin  hi

User · Answer

Something like this perhaps     usr bin env ruby  if  stdin tty    ARGV each do  file      puts  do something with this file    file     end else    stdin each line do  line      puts  do something with this line    line     end end   Example    gt  cat input txt     myprog rb do something with this line  this do something with this line  is do something with this line  a do something with this line  test  gt    myprog rb  lt  input txt  do something with this line  this do something with this line  is do something with this line  a do something with this line  test  gt    myprog rb arg1 arg2 arg3 do something with this file  arg1 do something with this file  arg2 do something with this file  arg3

User · Answer

while STDIN gets   puts    end  while ARGF gets   puts    end   This is inspired by Perl   while  lt STDIN gt      print     n

User · Answer

I ll add that in order to use ARGF with parameters  you need to clear ARGV before calling ARGF each  This is because ARGF will treat anything in ARGV as a filename and read lines from there first   Here s an example  tee  implementation   File open ARGV 0    w   do  file    ARGV clear    ARGF each do  line      puts line     file write line    end end

User · Answer

while STDIN gets   puts    end  while ARGF gets   puts    end   This is inspired by Perl   while  lt STDIN gt      print     n

User · Answer

I am not quite sure what you need  but I would use something like this      usr bin env ruby  until ARGV empty  do   puts  From arguments    ARGV shift   end  while a   gets   puts  From stdin    a   end   Note that because ARGV array is empty before first gets  Ruby won t try to interpret argument as text file from which to read  behaviour inherited from Perl    If stdin is empty or there is no arguments  nothing is printed   Few test cases     cat input txt     myprog rb From stdin  line 1 From stdin  line 2      myprog rb arg1 arg2 arg3 From arguments  arg1 From arguments  arg2 From arguments  arg3 hi  From stdin  hi

User · Answer

You can also use STDIN each line  and STDIN each line to a to get it as an array  e g  STDIN each line do  line    puts line end

User · Answer

It seems most answers are assuming the arguments are filenames containing content to be cat d to the stdin   Below everything is treated as just arguments   If STDIN is from the TTY  then it is ignored     cat tstarg rb  while a  ARGV shift or   STDIN tty  and STDIN gets      puts a end   Either arguments or stdin can be empty or have data     cat numbers  1 2 3 4 5     tstarg rb a b c  lt  numbers a b c 1 2 3 4 5

User · Answer

Something like this perhaps     usr bin env ruby  if  stdin tty    ARGV each do  file      puts  do something with this file    file     end else    stdin each line do  line      puts  do something with this line    line     end end   Example    gt  cat input txt     myprog rb do something with this line  this do something with this line  is do something with this line  a do something with this line  test  gt    myprog rb  lt  input txt  do something with this line  this do something with this line  is do something with this line  a do something with this line  test  gt    myprog rb arg1 arg2 arg3 do something with this file  arg1 do something with this file  arg2 do something with this file  arg3

User · Answer

Following are some things I found in my collection of obscure Ruby  So  in Ruby  a simple no-bells implementation of the Unix command cat would be     usr bin env ruby puts ARGF read  ARGF is your friend when it comes to input  it is a virtual file that gets all input from named files or all from STDIN  ARGF each with index do  line  idx      print ARGF filename   quot   quot   idx   quot   quot   line end    print all the lines in every file passed via command line that contains login ARGF each do  line      puts line if line     login  end  Thank goodness we didn   t get the diamond operator in Ruby  but we did get ARGF as a replacement  Though obscure  it actually turns out to be useful  Consider this program  which prepends copyright headers in-place  thanks to another Perlism  -i  to every file mentioned on the command-line     usr bin env ruby -i  Header   DATA read  ARGF each line do  e    puts Header if ARGF pos - e length    0   puts e end    END    --   Copyright  C  2007 Fancypants  Inc       Credit to   https   web archive org web 20080725055721 http   www oreillynet com ruby blog 2007 04 trivial scripting with ruby html comment-565558 http   blog nicksieger com articles 2007 10 06 obscure-and-ugly-perlisms-in-ruby

User · Answer

Quick and simple   STDIN gets chomp     YES

User · Answer

I do something like this     all lines      ARGV each do  line    all lines  lt  lt  line     n  end puts all lines

User · Answer

Ruby provides another way to handle STDIN  The -n flag  It treats your entire program as being inside a loop over STDIN   including files passed as command line args   See e g  the following 1-line script      usr bin env ruby -n   example rb  puts  hello          prepend  hello   to each line from STDIN   these will all work      example rb  lt  input txt   cat input txt     example rb     example rb input txt

User · Answer

Following are some things I found in my collection of obscure Ruby  So  in Ruby  a simple no-bells implementation of the Unix command cat would be     usr bin env ruby puts ARGF read  ARGF is your friend when it comes to input  it is a virtual file that gets all input from named files or all from STDIN  ARGF each with index do  line  idx      print ARGF filename   quot   quot   idx   quot   quot   line end    print all the lines in every file passed via command line that contains login ARGF each do  line      puts line if line     login  end  Thank goodness we didn   t get the diamond operator in Ruby  but we did get ARGF as a replacement  Though obscure  it actually turns out to be useful  Consider this program  which prepends copyright headers in-place  thanks to another Perlism  -i  to every file mentioned on the command-line     usr bin env ruby -i  Header   DATA read  ARGF each line do  e    puts Header if ARGF pos - e length    0   puts e end    END    --   Copyright  C  2007 Fancypants  Inc       Credit to   https   web archive org web 20080725055721 http   www oreillynet com ruby blog 2007 04 trivial scripting with ruby html comment-565558 http   blog nicksieger com articles 2007 10 06 obscure-and-ugly-perlisms-in-ruby

User · Answer

You can also use STDIN each line  and STDIN each line to a to get it as an array  e g  STDIN each line do  line    puts line end

User · Answer

It seems most answers are assuming the arguments are filenames containing content to be cat d to the stdin   Below everything is treated as just arguments   If STDIN is from the TTY  then it is ignored     cat tstarg rb  while a  ARGV shift or   STDIN tty  and STDIN gets      puts a end   Either arguments or stdin can be empty or have data     cat numbers  1 2 3 4 5     tstarg rb a b c  lt  numbers a b c 1 2 3 4 5

User · Answer

I ll add that in order to use ARGF with parameters  you need to clear ARGV before calling ARGF each  This is because ARGF will treat anything in ARGV as a filename and read lines from there first   Here s an example  tee  implementation   File open ARGV 0    w   do  file    ARGV clear    ARGF each do  line      puts line     file write line    end end

User · Answer

Following are some things I found in my collection of obscure Ruby  So  in Ruby  a simple no-bells implementation of the Unix command cat would be     usr bin env ruby puts ARGF read  ARGF is your friend when it comes to input  it is a virtual file that gets all input from named files or all from STDIN  ARGF each with index do  line  idx      print ARGF filename   quot   quot   idx   quot   quot   line end    print all the lines in every file passed via command line that contains login ARGF each do  line      puts line if line     login  end  Thank goodness we didn   t get the diamond operator in Ruby  but we did get ARGF as a replacement  Though obscure  it actually turns out to be useful  Consider this program  which prepends copyright headers in-place  thanks to another Perlism  -i  to every file mentioned on the command-line     usr bin env ruby -i  Header   DATA read  ARGF each line do  e    puts Header if ARGF pos - e length    0   puts e end    END    --   Copyright  C  2007 Fancypants  Inc       Credit to   https   web archive org web 20080725055721 http   www oreillynet com ruby blog 2007 04 trivial scripting with ruby html comment-565558 http   blog nicksieger com articles 2007 10 06 obscure-and-ugly-perlisms-in-ruby

User · Answer

Following are some things I found in my collection of obscure Ruby  So  in Ruby  a simple no-bells implementation of the Unix command cat would be     usr bin env ruby puts ARGF read  ARGF is your friend when it comes to input  it is a virtual file that gets all input from named files or all from STDIN  ARGF each with index do  line  idx      print ARGF filename   quot   quot   idx   quot   quot   line end    print all the lines in every file passed via command line that contains login ARGF each do  line      puts line if line     login  end  Thank goodness we didn   t get the diamond operator in Ruby  but we did get ARGF as a replacement  Though obscure  it actually turns out to be useful  Consider this program  which prepends copyright headers in-place  thanks to another Perlism  -i  to every file mentioned on the command-line     usr bin env ruby -i  Header   DATA read  ARGF each line do  e    puts Header if ARGF pos - e length    0   puts e end    END    --   Copyright  C  2007 Fancypants  Inc       Credit to   https   web archive org web 20080725055721 http   www oreillynet com ruby blog 2007 04 trivial scripting with ruby html comment-565558 http   blog nicksieger com articles 2007 10 06 obscure-and-ugly-perlisms-in-ruby

[ruby] Best practices with STDIN in Ruby?

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