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Asked: 2016-06-07 13:57:36 +0800 CST

Ubuntu bc weird behavior

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There is a weird behavior in Bash script. Trying to run following lines in two different systems.

Script:

cpuIdle=$(mpstat 5 1 | grep Average | awk '{  print $12 }')
cpuUsage=$(bc <<< "100.0-$cpuIdle")

And here are the details of machines.

System-1:

  • Ubuntu 14.04.04 LTS
  • Linux 4.2.0-36-generic #42~14.04.1-Ubuntu SMP Fri May 13 17:27:22 UTC 2016 x86_64 x86_64 x86_64 GNU/Linux
  • awk --version = GNU Awk 4.0.1
  • bash --version = GNU bash, version 4.3.11(1)-release (x86_64-pc-linux-gnu)

System-2:

  • Ubuntu 16.04.04 LTS
  • Linux 4.4.0-22-generic #40-Ubuntu SMP Thu May 12 22:03:46 UTC 2016 x86_64 x86_64 x86_64 GNU/Linux
  • awk --version = GNU Awk 4.1.3, API: 1.1 (GNU MPFR 3.1.4, GNU MP 6.1.0)
  • bash --version = GNU bash, version 4.3.42(1)-release (x86_64-pc-linux-gnu)

Script runs fluently on System-1 but gives following error on System-2 while running bc:

(standard_in) 1: syntax error

I can confirm that in both systems cpuIdle vairable is being set correctly (1st line of the script).

I also can confirm that bc working without a problem in both systems when I set cpuIdle variable manually (like cpuIdle=97.3).

Can't decide if this is a bug or my mistake. Any suggestion or ideas?

14.04

1 Answers

  1. Best Answer

    It is the comma.

    $ cpuIdle=$(mpstat 5 1 | grep Average | awk '{  print $12 }')
$ echo $cpuIdle
99,25

    ->

    $ cpuUsage=$(bc <<< "100.0-95,25")
(standard_in) 1: syntax error

    and

    $ cpuUsage=$(bc <<< "100.0-95.25")
$ echo $cpuUsage
4.75

    So this could be an internationalization issue (in Holland we use a comma for decimals). I would say: bug, someone forgot to include a comma as a possible decimal sign.

    Switch to American annotation and it will work again.

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