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Calling Shell commands from Ruby
this example from a Well House Consultants training course
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$ Learn about this subject
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