Calling Shell commands from Ruby

this example from a Well House Consultants training course
More on this [link]

This example is described in the following article(s):
• Running shell (operating system) commands from within Ruby - [link]

Source code: cashell Module: R113

def test(title) puts "\n------------------------: #{title}" ; end

# Calling Shell commands from Ruby
# lots of ways!

test "one - returns stdout as string; stderr to ruby stdout"
first = `grep -c option247 ac_20160516 ac_20160517`
p first

test "two - returns stdout as string; stderr to ruby stdout"
second = %x!grep -c option247 ac_20160516 ac_20160517!
p second

test "three - returns success; stdout routed to ruby stdout"
third = system("grep -c option247 ac_20160516 ac_20160517")
p third

test "four - returns stdout and stderr as string"
fourth = %x!grep -c option247 ac_20160516 ac_20160517 2>&1!
p fourth

test "five - returns a file handle to output; stderr to ruby stderr"
handle = IO.popen("grep -c option247 ac_20160516 ac_20160517")
five = handle.readlines
p five

test "six - returns a file handle to output; stderr to ruby stderr"
require 'open3'
h_in,h_out,h_err = Open3.popen3("grep -c option247 ac_20160516 ac_20160517")
p h_out.readlines
p h_err.readlines

test "seven - piping"
h_in,h_out,h_err = Open3.popen3("cat -n")
(11..15).each do | linelabeller |
h_in.write "This is line #{linelabeller}\n"
end
h_in.close
seven = h_out.readlines
p seven

print "\n"

__END__

Run with ac_20160516 exisiting and ac_20160517 not present. Sample output:

WomanWithCat:4c grahamellis$ ruby cashell

------------------------: one - returns stdout as string; stderr to ruby stdout
grep: ac_20160517: No such file or directory
"ac_20160516:399\n"

------------------------: two - returns stdout as string; stderr to ruby stdout
grep: ac_20160517: No such file or directory
"ac_20160516:399\n"

------------------------: three - returns success; stdout routed to ruby stdout
ac_20160516:399
grep: ac_20160517: No such file or directory
false

------------------------: four - returns stdout and stderr as string
"grep: ac_20160517: No such file or directory\nac_20160516:399\n"

------------------------: five - returns a file handle to output; stderr to ruby stderr
grep: ac_20160517: No such file or directory
["ac_20160516:399\n"]

------------------------: six - returns a file handle to output; stderr to ruby stderr
["ac_20160516:399\n"]
["grep: ac_20160517: No such file or directory\n"]

------------------------: seven - piping
[" 1\tThis is line 11\n", " 2\tThis is line 12\n", " 3\tThis is line 13\n", " 4\tThis is line 14\n", " 5\tThis is line 15\n"]

WomanWithCat:4c grahamellis$

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