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Super Speedy Hexadecimal or Octal Calculations and Conversions to Decimal.

Terminal - Super Speedy Hexadecimal or Octal Calculations and Conversions to Decimal.
echo "$(( 0x10 )) - $(( 010 )) = $(( 0x10 - 010 ))"
2009-06-08 19:35:53
User: asmoore82
Functions: echo
10
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Super Speedy Hexadecimal or Octal Calculations and Conversions to Decimal.

^Hexadecimal Ten minus Octal Ten is Eight(in Decimal).

echo "$(( 0xaf )) = $(( 0257 ))"

^Hexadecimal AF and Octal 257 are both Decimal 175.

Show sample output | Add to favourites | Report as malicious

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What others think

The basic point here is that (I'm assuming bash) the shell understands hexadecimal and octal numbers, when strings of digits (0-9,a-f) are preceded by 0x or 0.

Comment by bwoodacre 138 weeks and 4 days ago

That's excellent, which I knew about it sooner!

Comment by nanreh 138 weeks and 3 days ago

Yes, the general idea is that BASH's $(( ... )) construct accepts hex with "0x" and *ASSUMES* numbers with leading zeros are octal. This assumption can cause weird bugs when scripting; especially when time and dates are involved. This produces an error only in the months of August and September:

currentmonth=$( date +%m ) echo "There are $(( 12 - currentmonth )) months left in the year."
Comment by asmoore82 138 weeks and 3 days ago

After some googling, it seems you can force a particular base on an expression via prefixing "base#" to a number. In august/september 'date +%m' will yield 08 and 09, so to fix this the echo would read:

echo "There are $(( 12 - 10#currentmonth )) months left in the year."

to force current month to be interpreted in base 10. Obviously the base must be specified in base 10, although it would be an interesting way to screw up somebody's bash session (if it were possible) to change the default number base. :-)

Comment by bwoodacre 136 weeks and 4 days ago

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