What s the difference between Perl s backticks system and exec

Question

Can someone please help me  In Perl  what is the difference between   exec  command     and  system  command      and  print  command     Are there other ways to run shell commands too

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Let me quote the manuals first   perldoc exec        The exec function executes a system command and never returns-- use system instead of exec if you want it to return   perldoc system        Does exactly the same thing as exec LIST   except that a fork is done first  and the parent process waits for the child process to complete    In contrast to exec and system  backticks don t give you the return value but the collected STDOUT   perldoc   x0060 String  x0060       A string which is  possibly  interpolated and then executed as a system command with  bin sh or its equivalent  Shell wildcards  pipes  and redirections will be honored  The collected standard output of the command is returned  standard error is unaffected      Alternatives   In more complex scenarios  where you want to fetch STDOUT  STDERR or the return code  you can use well known standard modules like IPC  Open2 and IPC  Open3   Example   use IPC  Open2  my  pid   open2   CHLD OUT    CHLD IN   some    cmd    and    args    waitpid   pid  0    my  child exit status       gt  gt  8    Finally  IPC  Run from the CPAN is also worth looking at

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exec  executes a command and never returns    It s like a return statement in a function   If the command is not found exec returns false    It never returns true  because if the command is found it never returns at all    There is also no point in returning STDOUT  STDERR or exit status of the command    You can find documentation about it in  perlfunc     because it is a function   system  executes a command and your Perl script is continued after the command has finished   The return value is the exit status of the command    You can find documentation about it in  perlfunc   backticks  like system executes a command and your perl script is continued after the command has finished   In contrary to system the return value is STDOUT of the command    qx   is equivalent to backticks    You can find documentation about it in perlop  because unlike system and execit is an operator     Other ways  What is missing from the above is a way to execute a command asynchronously  That means your perl script and your command run simultaneously  This can be accomplished with open  It allows you to read STDOUT STDERR and write to STDIN of your command  It is platform dependent though   There are also several modules which can ease this tasks  There is IPC  Open2 and IPC  Open3 and IPC  Run  as well as Win32  Process  Create if you are on windows

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The difference between  exec  and  system  is that exec replaces your current program with  command  and NEVER returns to your program  system  on the other hand  forks and runs  command  and returns you the exit status of  command  when it is done running  The back tick runs  command  and then returns a string representing its standard out  whatever it would have printed to the screen   You can also use popen to run shell commands and I think that there is a shell module -  use shell  that gives you transparent access to typical shell commands   Hope that clarifies it for you

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In general I use system  open  IPC  Open2  or IPC  Open3 depending on what I want to do   The qx   operator  while simple  is too constraining in its functionality to be very useful outside of quick hacks   I find open to much handier   system  run a command and wait for it to return  Use system when you want to run a command  don t care about its output  and don t want the Perl script to do anything until the command finishes    doesn t spawn a shell  arguments are passed as they are system  command    arg1    arg2    arg3      or   spawns a shell  arguments are interpreted by the shell  use only if you  want the shell to do globbing  e g    txt  for you or you want to redirect  output system  command arg1 arg2 arg3      qx   or     run a command and capture its STDOUT  Use qx   when you want to run a command  capture what it writes to STDOUT  and don t want the Perl script to do anything until the command finishes    arguments are always processed by the shell   in list context it returns the output as a list of lines my  lines   qx command arg1 arg2 arg3     in scalar context it returns the output as one string my  output   qx command arg1 arg2 arg3     exec  replace the current process with another process   Use exec along with fork when you want to run a command  don t care about its output  and don t want to wait for it to return   system is really just   sub my system       die  could not fork n  unless defined my  pid   fork       return waitpid  pid  0 if  pid   parent waits for child     exec      replace child with new process     You may also want to read the waitpid and perlipc manuals   open  run a process and create a pipe to its STDIN or STDERR  Use open when you want to write data to a process s STDIN or read data from a process s STDOUT  but not both at the same time     read from a gzip file as if it were a normal file open my  read fh   -     gzip    -d    filename     or die  could not open  filename         write to a gzip compressed file as if were a normal file open my  write fh    -    gzip    filename     or die  could not open  filename         IPC  Open2  run a process and create a pipe to both STDIN and STDOUT  Use IPC  Open2 when you need to read from and write to a process s STDIN and STDOUT   use IPC  Open2   open2 my  out  my  in    usr bin bc      or die  could not run bc    print  in  5 6 n    my  answer    lt  out gt     IPC  Open3  run a process and create a pipe to STDIN  STDOUT  and STDERR  use IPC  Open3 when you need to capture all three standard file handles of the process  I would write an example  but it works mostly the same way IPC  Open2 does  but with a slightly different order to the arguments and a third file handle

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What s the difference between Perl s backticks      system  and exec   exec - gt  exec  command     system - gt  system  command    and  backticks - gt  print  command     exec  exec executes a command and never resumes the Perl script  It s to a script like a return statement is to a function   If the command is not found  exec returns false  It never returns true  because if the command is found  it never returns at all  There is also no point in returning STDOUT  STDERR or exit status of the command  You can find documentation about it in perlfunc  because it is a function   E g        usr bin perl print  Need to start exec command   my  data2   exec  ls    print  Now END exec command   print  Hello  data2 n n     In above code  there are three print statements  but due to exec leaving the script  only the first print statement is executed  Also  the exec command output is not being assigned to any variable   Here  only you re only getting the output of the first print statement and of executing the ls command on standard out   system  system executes a command and your Perl script is resumed after the command has finished  The return value is the exit status of the command  You can find documentation about it in perlfunc   E g        usr bin perl print  Need to start system command   my  data2   system  ls    print  Now END system command   print  Hello  data2 n n     In above code  there are three print statements  As the script is resumed after the system command  all three print statements are executed   Also  the result of running system is assigned to data2  but the assigned value is 0  the exit code from ls    Here  you re getting the output of the first print statement  then that of the ls command  followed by the outputs of the final two print statements on standard out   backticks      Like system  enclosing a command in backticks executes that command and your Perl script is resumed after the command has finished  In contrast to system  the return value is STDOUT of the command  qx   is equivalent to backticks  You can find documentation about it in perlop  because unlike system and exec  it is an operator   E g        usr bin perl print  Need to start backticks command   my  data2    ls   print  Now END system command   print  Hello  data2 n n     In above code  there are three print statements and all three are being executed  The output of ls is not going to standard out directly  but assigned to the variable data2 and then printed by the final print statement

[perl] What's the difference between Perl's backticks, system, and exec?

Let me quote the manuals first:

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