Ruby Difference between exec system and x or Backticks

Question

What is the difference between the following Ruby methods?

exec, system and %x() or Backticks

I know they are used to execute terminal commands programmatically via Ruby, but I'd like to know why there are three different ways to do this.

User · Answer

They do different things   exec replaces the current process with the new process and never returns   system invokes another process and returns its exit value to the current process   Using backticks invokes another process and returns the output of that process to the current process

User · Answer

system The system method calls a system program  You have to provide the command as a string argument to  this method  For example   gt  gt  system  quot date quot   Wed Sep 4 22 03 44 CEST 2013   gt  true  The invoked program will use the current STDIN  STDOUT and STDERR objects of your Ruby program  In fact  the actual return value is either true  false or nil  In the example the date was printed through the IO object of STDIN  The method will return true if the process exited with a zero status  false if the process exited with a non-zero status and nil if the execution failed  As of Ruby 2 6  passing exception  true will raise an exception instead of returning false or nil   gt  gt  system  invalid     gt  nil   gt  gt  system  invalid   exception  true  Traceback  most recent call last       Errno  ENOENT  No such file or directory - invalid   Another side effect is that the global variable    is set to a Process  Status object  This object will contain information about the  call itself  including the process identifier  PID  of the invoked process and the exit status   gt  gt  system  quot date quot   Wed Sep 4 22 11 02 CEST 2013   gt  true  gt  gt       gt    lt Process  Status  pid 15470 exit 0 gt   Backticks Backticks      call a system program and return its output  As opposed to the first approach  the command is not provided through a string  but by putting it inside a backticks pair   gt  gt   date    gt  Wed Sep 4 22 22 51 CEST 2013     The global variable    is set through the backticks  too  With backticks you can also make use string interpolation   x   Using  x is an alternative to the backticks style  It will return the output  too  Like its relatives  w and  q  among others   any delimiter will suffice as long as bracket-style delimiters match  This means  x date    x date  and  x-date- are all synonyms  Like backticks  x can make use of string interpolation  exec By using Kernel exec the current process  your Ruby script  is replaced with the process invoked through exec  The method can take a string as argument  In this case the string will be subject to shell expansion  When using more than one argument  then the first one is used to execute a program and the following are provided as arguments to the program to be invoked  Open3 popen3 Sometimes the required information is written to standard input or standard error and you need to get control over those as well  Here Open3 popen3 comes in handy  require  open3   Open3 popen3  quot curl http   example com quot   do  stdin  stdout  stderr  thread     pid   thread pid    puts stdout read chomp end

User · Answer

Here s a flowchart based on this answer   See also  using script to emulate a terminal

[ruby] Ruby, Difference between exec, system and %x() or Backticks

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