CODEWITHSUNDEEP
python-3.x
Wizard
Wizard

Reputation: 22083

Single PID run two commands

When I check the process from the bash, it display:

In [42]: !ps
  PID TTY           TIME CMD
  417 ttys000    0:00.49 -bash
 7783 ttys000    0:06.50 /Users/me/anaconda3/bin/python /Users/me/anaconda3/bin/ipython

It seems that pid 7783 run two commands simultaneous,

Could please provide any hints help understand it?

Upvotes: 0

Views: 32

Answers (1)

MisterMiyagi
MisterMiyagi

Reputation: 50076

It is running only one command but with one argument:

/Users/me/anaconda3/bin/python /Users/me/anaconda3/bin/ipython
^ command                      ^ argument

Python scripts are not directly executable. An interpreter is required to actually run them. Similarly, in your case the command is the python interpreter, and the argument is the ipython script.

When you directly execute the script, the operating system peeks inside to see if it has a shebang. This is a line starting with #! (actually the byte sequence 0x2321) followed by the path to the program meant to run the file. For example, on my system the ipython script points at the python3.7 interpreter:

$ head -1 $(which ipython3)
#!/usr/local/opt/python/bin/python3.7

Calling the script automatically expands to calling the shebang program with the script. Thus, you never see the actual script being run by itself - only the interpreter running the script.

$ ipython3 -c '!ps' | grep ipython3
5764 ttys004    0:00.37 /usr/local/Cellar/python/3.7.0/Frameworks/Python.framework/Versions/3.7/Resources/Python.app/Contents/MacOS/Python /Users/miyagi/Library/Python/3.7/bin/ipython3 -c !ps

Upvotes: 1

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