jfhufl

    ruby -e 'x = "a\n25\n" ; if x =~ /^\d+$/ ; puts "yes" ; else ; puts "no" ; end'
    yes

    $ ruby -e 'x = "25" ; if x =~ /^\d+$/ ; puts "yes" ; else ; puts "no" ; end'
    yes
    $ ruby -e 'x = "25\n" ; if x =~ /^\d+$/ ; puts "yes" ; else ; puts "no" ; end' 
    yes
    $ ruby -e 'x = "a25\n" ; if x =~ /^\d+$/ ; puts "yes" ; else ; puts "no" ; end'
    no

    https://en.wikipedia.org/wiki/Number_form
    https://www.discovermagazine.com/health/the-rare-humans-who-see-time-and-have-amazing-memories

    % cat /tmp/sh
    var=variables
    x=$(
    cat <<EOT
    This string has 'single' and "double" quotes and can interpolate '$var'
    EOT
    )
    echo $x

    % bash /tmp/sh
    This string has 'single' and "double" quotes and can interpolate 'variables'

    command | ruby -e 'ARGF.each { |line| #do stuff with line }'

    (long pipeline that generates lots of output) | xclip

    xclip < /some/file

    cat /etc/passwd | grep root | awk -F: '{print $3}'

    ruby -e 'puts File.read("/etc/passwd").lines.select { |line| line.match(/root/) }.first.split(":")[2]'

  https://en.wikipedia.org/wiki/Organlegging

    % echo 'one\ntwo\nthree' | sed -e 's,$, four,'
    one four
    two four
    three four