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0 pointsshakna5y ago0 comments

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.

0 comments

Laremere5y 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.

eulers_secret5y 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))

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...

zamalek5y 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.

jandrese5y ago

It's plaintext, you could just look at it. That's the beauty of text based systems.

rakoo5y ago

This is where you need to use awk.

    awk -F ':' '/cpu cores/ {a = $2 + 1} END {print a}' /proc/cpuinfo

lsofzz5y 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.

jandrese5y ago

That seems overly complicated to me. Can you not just:

     grep '^processor' /proc/cpuinfo | wc -l

j / k navigate · click thread line to collapse

0 pointsshakna5y ago0 comments

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

0 comments

Laremere5y ago

Compare to using a real programing language, such as Go:

  return runtime.NumCPU() + 1

eulers_secret5y 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))

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...

zamalek5y 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.

jandrese5y ago

It's plaintext, you could just look at it. That's the beauty of text based systems.

rakoo5y ago

This is where you need to use awk.

    awk -F ':' '/cpu cores/ {a = $2 + 1} END {print a}' /proc/cpuinfo

lsofzz5y 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.

jandrese5y ago

That seems overly complicated to me. Can you not just:

     grep '^processor' /proc/cpuinfo | wc -l

j / k navigate · click thread line to collapse