Why is returning the same id as the parent process

Question

I have problem with Bash  and I don t know why  Under shell  I enter   echo          print 2433  echo         also print 2433    getpid     print 2602    getpid  is a C program to get current pid  like         int main         printf   d    int getpid         return 0          What confuses me is that      I think   command   is a sub-process  am i right    and i think its pid should be different with its parent pid  but they are the same  why      when i use my program to show pid between parenthesis  the pid it shows is different  is it right    is      something like macro      Can you help me

User · Answer

Parentheses invoke a subshell in Bash  Since it s only a subshell it might have the same PID - depends on implementation  The C program you invoke is a separate process  which has its own unique PID - doesn t matter if it s in a subshell or not     is an alias in Bash to the current script PID  See differences between    and  BASHPID here  and right above that the additional variable  BASH SUBSHELL which contains the nesting level

User · Answer

You can use one of the following       is the PID of the last backgrounded process  kill -0  PID checks whether it s still running     is the PID of the current shell

User · Answer

this one univesal way to get correct pid  pid   cut -d    -f4  lt   proc self stat   same nice worked for sub  SUB        pid   cut -d    -f4  lt   proc self stat      echo         pid     echo  pid         SUB    check output   pid   8099 8099    8100

User · Answer

If you were asking how to get the PID of a known command it would resemble something like this   If you had issued the command below      The command issued was         dd if  dev diskx of  dev disky     Then you would use   PIDs   ps   grep dd   grep if   cut -b 1-5    What happens here is it pipes all needed unique characters to a field and that field can be echoed using  echo  PIDs

User · Answer

is defined to return the process ID of the parent in a subshell  from the man page under  Special Parameters              Expands to the process ID of the shell   In a    subshell  it expands to the process ID of the current shell  not the subshell     In bash 4  you can get the process ID of the child with BASHPID       echo    17601       echo     echo  BASHPID   17601 17634

User · Answer

Try getppid   if you want your C program to print your shell s PID

[bash] Why is $$ returning the same id as the parent process?

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