ruby command

# To open an Interactive Ruby Shell (REPL):
irb

# To execute a Ruby script:
ruby <script.rb>

# To execute a single Ruby command in the command line:
ruby -e <command>

# To check for syntax errors on a given Ruby script:
ruby -c <script.rb>

# To show the version of Ruby you are using:
ruby -v

##
# Ruby Command One-Liners
##

################
# FILE SPACING #
################

# double space a file
$ ruby -pe 'puts' < file.txt

# triple space a file
$ ruby -pe '2.times {puts}' < file.txt

# undo double-spacing (w/ and w/o whitespace in lines)
$ ruby -lne 'BEGIN{$/="\n\n"}; puts $_' < file.txt
$ ruby -ne 'BEGIN{$/="\n\n"}; puts $_.chomp' < file.txt
$ ruby -e 'puts STDIN.readlines.to_s.gsub(/\n\n/, "\n")' < file.txt

##############
## NUMBERING #
##############

# number each line of a file (left justified).
$ ruby -ne 'printf("-%6s%s", $., $_)' < file.txt

# number each line of a file (right justified).
$ ruby -ne 'printf("%6s%s", $., $_)' < file.txt

# number each line of a file, only print non-blank lines
$ ruby -e 'while gets; end; puts $.' < file.txt

# count lines (emulates 'wc -l')
$ ruby -ne 'END {puts $.}' < file.txt
$ ruby -e 'while gets; end; puts $.' < file.txt

####################################
# TEXT CONVERSION AND SUBSTITUTION #
####################################

# convert DOS newlines (CR/LF) to Unix format (LF)
# - strip newline regardless; re-print with unix EOL
$ ruby -ne 'BEGIN{$\="\n"}; print $_.chomp' < file.txt

# convert Unix newlines (LF) to DOS format (CR/LF)
# - strip newline regardless; re-print with dos EOL
$ ruby -ne 'BEGIN{$\="\r\n"}; print $_.chomp' < file.txt

# delete leading whitespace (spaces/tabs/etc) from beginning of each line
$ ruby -pe 'gsub(/^\s+/, "")' < file.txt

# delete trailing whitespace (spaces/tabs/etc) from end of each line
# - strip newline regardless; replace with default platform record separator
$ ruby -pe 'gsub(/\s+$/, $/)' < file.txt

# delete BOTH leading and trailing whitespace from each line
$ ruby -pe 'gsub(/^\s+/, "").gsub(/\s+$/, $/)' < file.txt

# insert 5 blank spaces at the beginning of each line (ie. page offset)
$ ruby -pe 'gsub(/%/, "   ")' < file.txt
FAILS! $ ruby -pe 'gsub(/%/, 5.times{putc " "})' < file.txt

# align all text flush right on a 79-column width
$ ruby -ne 'printf("%79s", $_)' < file.txt

# center all text in middle of 79-column width
$ ruby -ne 'puts $_.chomp.center(79)' < file.txt
$ ruby -lne 'puts $_.center(79)' < file.txt

# substitute (find and replace) "foo" with "bar" on each line
$ ruby -pe 'gsub(/foo/, "bar")' < file.txt

# substitute "foo" with "bar" ONLY for lines which contain "baz"
$ ruby -pe 'gsub(/foo/, "bar") if $_ =~ /baz/' < file.txt

# substitute "foo" with "bar" EXCEPT for lines which contain "baz"
$ ruby -pe 'gsub(/foo/, "bar") unless $_ =~ /baz/' < file.txt

# substitute "foo" or "bar" or "baz".... with "baq"
$ ruby -pe 'gsub(/(foo|bar|baz)/, "baq")' < file.txt

# reverse order of lines (emulates 'tac') IMPROVE
$ ruby -ne 'BEGIN{@arr=Array.new}; @arr.push $_; END{puts @arr.reverse}' < file.txt

# reverse each character on the line (emulates 'rev')
$ ruby -ne 'puts $_.chomp.reverse' < file.txt
$ ruby -lne 'puts $_.reverse' < file.txt

# join pairs of lines side-by-side (like 'paste')
$ ruby -pe '$_ = $_.chomp + " " + gets if $. % 2' < file.txt

# if a line ends with a backslash, append the next line to it
$ ruby -pe 'while $_.match(/\\$/); $_ = $_.chomp.chop + gets; end' < file.txt
$ ruby -e 'puts STDIN.readlines.to_s.gsub(/\\\n/, "")' < file.txt

# if a line begins with an equal sign, append it to the previous line (Unix)
$ ruby -e 'puts STDIN.readlines.to_s.gsub(/\n=/, "")' < file.txt

# add a blank line every 5 lines (after lines 5, 10, 15, etc)
$ ruby -pe 'puts if $. % 6 == 0' < file.txt

# http://reference.jumpingmonkey.org/programming_languages/ruby/ruby-one-liners.html