4 ms·

I am firmly in the "ugh" camp. I strongly suspect that the fawning that occurs over pipelines is because of sentimentality more than practicality. Extracting in

I am firmly in the "ugh" camp. I strongly suspect that the fawning that occurs over pipelines is because of sentimentality more than practicality. Extracting information from text using a regular expression is fragile. Writing fragile code brings me absolutely no joy as a programmer - unless I am trying to flex my regex skills. If you really look at how pipelines are typically used is: lines are analogous to objects and [whatever the executable happens to use] delimiters are analogous to fields. Piping bare objects ("plain old shell objects") makes far more sense, involves far less typing and is far less fragile.

shakna 6y ago
If you're having to extract your data using a regex, then the data probably isn't well-formed enough for a shell pipeline. It's doable, but a bad idea. Regex should not be the first hammer you reach for, because it's a scalpel. I recently wanted cpu cores + 1. That could be a single regex. But this is more maintainable, and readable: echo '1 + '"$(grep 'cpu cores' /proc/cpuinfo | tail -n1 | awk -F ':' '{print $2}')" | bc There's room for a regex there. Grep could have done it, and then I wouldn't need the others... But I wouldn't be able to come back in twelve months and instantly be able to tell you what it is doing.
- zamalek 6y ago
  Would anyone be able to approach this, without knowledge of /proc/cpuinfo, and understand what `$2` refers to? > Regex should not be the first hammer you reach for, because it's a scalpel. You used a regex tool: grep.
  - jandrese 6y ago
    It's plaintext, you could just look at it. That's the beauty of text based systems.
- jandrese 6y ago
  That seems overly complicated to me. Can you not just: grep '^processor' /proc/cpuinfo | wc -l
- Laremere 6y ago
  Compare to using a real programing language, such as Go: return runtime.NumCPU() + 1 Sure, there needs to be os to program (and possibly occasionally program to program) communication, but well defined binary formats are easier to parse in a more reliable manner. Plus they can be faster, and moved to an appropriate function.
- rakoo 6y ago
  This is where you need to use awk. awk -F ':' '/cpu cores/ {a = $2 + 1} END {print a}' /proc/cpuinfo
  - lsofzz 6y ago
    > This is where you need to use awk. I think need is a strong statement in this context. echo $(( 1 + $(grep 'cpu cores' /proc/cpuinfo | head -1 | awk -F ':' '{print $2}') )) Choosing shell vs. [insert modern] programming is a matter of trade-off of taste, time, $$$, collective consensus (in a team setting) and so forth. [edit]: Forgot code syntax on HN.
- deleted 6y ago
  [deleted]
- eulers_secret 6y ago
  OP wants number of CORES, not CPUs (excluding HT 'cores'). I know this is old, but if someone finds their way here looking for a solution... In BASH number of CPUs + 1 is as easy as: echo $(($(getconf _NPROCESSORS_ON)+1)) or echo $(($(nproc)+1)) getconf even works on OS X! Many of the other solutions confuse the two. As far as I can tell, using OPs solution is one of the better ways to get core count. Could also: echo $(($(lscpu -p | tail -n 1 | cut -d',' -f 2)+2)) ...but OPs solution is probably easier to read...

shakna 6y ago

If you're having to extract your data using a regex, then the data probably isn't well-formed enough for a shell pipeline. It's doable, but a bad idea. Regex should not be the first hammer you reach for, because it's a scalpel. I recently wanted cpu cores + 1. That could be a single regex. But this is more maintainable, and readable: echo '1 + '"$(grep 'cpu cores' /proc/cpuinfo | tail -n1 | awk -F ':' '{print $2}')" | bc There's room for a regex there. Grep could have done it, and then I wouldn't need the others... But I wouldn't be able to come back in twelve months and instantly be able to tell you what it is doing.

zamalek 6y ago
Would anyone be able to approach this, without knowledge of /proc/cpuinfo, and understand what `$2` refers to? > Regex should not be the first hammer you reach for, because it's a scalpel. You used a regex tool: grep.
- jandrese 6y ago
  It's plaintext, you could just look at it. That's the beauty of text based systems.
jandrese 6y ago
That seems overly complicated to me. Can you not just: grep '^processor' /proc/cpuinfo | wc -l
Laremere 6y ago
Compare to using a real programing language, such as Go: return runtime.NumCPU() + 1 Sure, there needs to be os to program (and possibly occasionally program to program) communication, but well defined binary formats are easier to parse in a more reliable manner. Plus they can be faster, and moved to an appropriate function.
rakoo 6y ago
This is where you need to use awk. awk -F ':' '/cpu cores/ {a = $2 + 1} END {print a}' /proc/cpuinfo
- lsofzz 6y ago
  > This is where you need to use awk. I think need is a strong statement in this context. echo $(( 1 + $(grep 'cpu cores' /proc/cpuinfo | head -1 | awk -F ':' '{print $2}') )) Choosing shell vs. [insert modern] programming is a matter of trade-off of taste, time, $$$, collective consensus (in a team setting) and so forth. [edit]: Forgot code syntax on HN.
deleted 6y ago
[deleted]
eulers_secret 6y ago
OP wants number of CORES, not CPUs (excluding HT 'cores'). I know this is old, but if someone finds their way here looking for a solution... In BASH number of CPUs + 1 is as easy as: echo $(($(getconf _NPROCESSORS_ON)+1)) or echo $(($(nproc)+1)) getconf even works on OS X! Many of the other solutions confuse the two. As far as I can tell, using OPs solution is one of the better ways to get core count. Could also: echo $(($(lscpu -p | tail -n 1 | cut -d',' -f 2)+2)) ...but OPs solution is probably easier to read...