Multiply variable ranges with Bash brace expansion

问题

I've a question extending the code in this question: Can you multiply two variable ranges in Bash using brace expansion (not seq) and not using loops?

This is what I've tried so far

Work out how variable boundary ranges work (finally, a good use of eval):

$ echo {1..10}
1 2 3 4 5 6 7 8 9 10
$ boundary=10
$ echo {1..$boundary}
{1..10}
$ eval echo {1..$boundary}
1 2 3 4 5 6 7 8 9 10

But how can you multiply two variable boundary ranges?

$ echo $(({1..10}*{1..10}))
1 2 3 4 5 6 7 8 9 10 2 4 6 8 10 12 14 16 18 20 3 6 9 12 15 18 21 24 27 30 4 8 12 16 20 24 28 32 36 40 5 10 15 20 25 30 35 40 45 50 6 12 18 24 30 36 42 48 54 60 7 14 21 28 35 42 49 56 63 70 8 16 24 32 40 48 56 64 72 80 9 18 27 36 45 54 63 72 81 90 10 20 30 40 50 60 70 80 90 100
$ boundary=10
$ echo $(({1..$boundary}*{1..$boundary}))
bash: {1..10}*{1..10}: syntax error: operand expected (error token is "{1..10}*{1..10}")
$ eval echo $(({1..$boundary}*{1..$boundary}))
bash: {1..10}*{1..10}: syntax error: operand expected (error token is "{1..10}*{1..10}")

回答1:

this seems to work, just escaped the $ and [] to delay their evaluation (so that they are echoed, then evaluated)

eval echo \$\[{1..$boundary}*{1..$boundary}\]

That said I now need to go lookup what $[] does ;-)

Second answer, with non deprecated $[] syntax (but two evals)

eval eval echo "\$$\("{1..$boundary}*{1..$boundary}"$\)"

eval eval echo \\\$\\$\\\({1..$boundary}*{1..$boundary}\\$\\\)

来源：https://stackoverflow.com/questions/5696300/multiply-variable-ranges-with-bash-brace-expansion

标签

bash

shell

math

brace-expansion