tags: python proc linux

On Linux, we can find processes and their names via the `/proc` filesystem.
Names are in `/proc/xxx/comm`, so we need only read this and pass it to `re.search`.
I wrote this so as to not need to `pip install pgrep` for what this function does.

```py
#!/usr/bin/env python
# Poor mans pgrep, can just use this instead of having to install the pgrep
# module
import re
import sys
from glob import glob
from re import I # so we can use mypgrep.I without having to import re

def pgrep(pat,flags=0):
  '''pgrep(pattern, flags=0)
  flags are those in the re module and are passed to re.compile
  just put the output of this into dict() to get a dict'''
  r = re.compile(pat,flags)
  procs = glob("/proc/[0-9]*/comm")
  matches = []
  for proc in procs:
    pid = int(proc.split("/")[2])
    try:
      with open(proc) as f:
        name = f.read().rstrip()
    except Exception as e:
      print(f"# Exception {e} ({type(e)}) reading {proc}",file=sys.stderr)
      continue
    if r.search(name):
      matches.append((pid,name))
  return matches

if __name__ == "__main__":
  # random demo and test
  print(pgrep_list("init"))
  print(pgrep_list("Init",I))
  d = dict(pgrep_list("init"))
  print(d)
  print(pgrep_dict("init"))
  print(pgrep_dict("Init",I))
  print("\n".join(f"{x:<10} {y}" for x,y in pgrep_list("bash")))
  exit()
```