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Comment by williamcotton | Hacker News Reader

This is running in a barebones Ubuntu container on my MacBook as BSDs don't use /proc:

  root@74c03a282fbe:/# ed
  a
  ls /proc/[0-9]/status | xargs -n 1 cat | awk '/^Name:/ { name = $2 } /^Pid:/ { pid = $2 } END { print "cmd: " name ", pid: " pid }'
  .
  w prc.sh
  132
  q
  root@74c03a282fbe:/# chmod +x ./prc.sh
  root@74c03a282fbe:/# hyperfine --warmup=100 "./prc.sh"
  Benchmark 1: ./prc.sh
    Time (mean ± σ):       2.2 ms ±   0.3 ms    [User: 1.3 ms, System: 2.7 ms]
    Range (min … max):     1.8 ms …   5.0 ms    880 runs
   
    Warning: Command took less than 5 ms to complete. Results might be inaccurate.
    Warning: Statistical outliers were detected. Consider re-running this benchmark on a quiet PC without any interferences from other programs. It might help to use the '--warmup' or '--prepare' options.

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I like your style, but it's not quite right:

  $ echo /proc/[0-9]/status | wc
        1       7     105
  $ echo /proc/[1-9]*/status | wc
        1     483    8778

It also will sporadically print error messages due to all the race conditions. Here's my stab at it:

  $ cat dumbps 
  #!/bin/sh
  
  case $# in
    1)
   ;;
    *)
   echo "Usage: dumbps user" >&2
   exit 2
   ;;
  esac
  
  2>&- find /proc -mindepth 2 -maxdepth 2 -type f -name status -user "$1" | awk '{
   while ((getline li < $0) > 0) {
    if (li ~ /^Name:/) {
     split($0, fn, "/")
     print fn[3], substr(li, 6)
     break
    }
   }
  
   close($0)
  }'
  $ ./dumbps "$USER" | grep -w 'bash$'
  1616678  bash
  $ ./dumbps 0 | grep -w 'systemd$'
  1  systemd
  $

It's pretty fast too:

  $ ls -ld /proc/[1-9]*/status | awk '$3 == "root"' | wc
      445    4005   29367
  $ time ./dumbps >/dev/null            
  Usage: dumdps user
  
  real 0m0.001s
  user 0m0.000s
  sys 0m0.001s
  $

You seem to have very similar races here though?

Perfectly possible, even likely, for a process to end between "find" finding it and awk opening it... especially given the pipe buffer between the two.

Personly I'd rather an "expect errors" approach.. break it out so that you can easily treat a failed open as a "continue next" scenario and hide just those errors

2>&- hides races in find itself

while ((getline li < $0) > 0) hides races in awk

in practice Name: is the first line so cmd is not truncated

Of course I got my test wrong though :D

  $ time ./dumbps 0 >/dev/null
  
  real 0m0.030s
  user 0m0.012s
  sys 0m0.022s

I think you may have convinced me to learn more awk with this. I'd have constructed something horrible with sed or so to do this. And this is just much cleaner

The AWK Programming Language, Second Edition was just released. I'd say it's an instant classic! CSV support is slowly rolling out... you can compile Kernighan's nawk from source right now, gawk has it in trunk I think, and GoAwk has had support and is now also following the --csv design decision made by Mr. Kernighan.

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