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2. Fundamental Concepts > Process Groups and Shell Job Control

Process Groups and Shell Job Control

Each program executed by the shell is started in a new process. For example, the shell creates three processes to execute the following pipeline of commands (which displays a list of files in the current working directory sorted by file size):

$ ls -l | sort -k5n | less

All major shells, except the Bourne shell, provide an interactive feature called job control, which allows the user to simultaneously execute and manipulate multiple commands or pipelines. In job-control shells, all of the processes in a pipeline are placed in a new process group or job. (In the simple case of a shell command line containing a single command, a new process group containing just a single process is created.) Each process in a process group has the same integer process group identifier, which is the same as the process ID of one of the processes in the group, termed the process group leader.


  

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