Cannot multiply a variable with concatenated word count

Question

I have something like this in bash on Linux:

some_variable= ls *somepattern* | xargs cat | wc -c

And i would like to multiply that by some amount like:

another_variable = $(($some_variable * 10))

But i get an error

  -bash: * 100: syntax error: operand expected (error token is "* 100")

Why is it not possible to not multiply some_variable with wc?

Answer 1

You never get to the multiplication, you aren't actually assigning a variable there. You can't have a space around the =, you need:

some_variable=some_value

Next, if you want to assign a variable to the output of a command, you ned to use command substitution:

some_variable=$(some_command)

Or, the still supported but becoming deprecated backticks:

some_variable=`some_command`

So, what you wanted was:

some_variable=$(ls *somepattern* | xargs cat | wc -c)

But that would be much better done like this:

some_variable=$(cat *somepattern* | wc -c)

Once you have that, you can do:

another_variable=$(($some_variable * 10))

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Finally, your error was caused because, as explained in the first section, your variable was empty, so you ended up running this:

$ another_variable = $(( * 10))
bash: * 10: syntax error: operand expected (error token is "* 10")