Blank variable during bash command substitution

问题

I am doing command substitution and saving the result to a variable. However, the results of the command contain double quotes and this is causing the variable to be empty.

When running test="$(java -version)" I get the following result:

openjdk version "1.8.0_65"
OpenJDK Runtime Environment (build 1.8.0_65-b17)
OpenJDK 64-Bit Server VM (build 25.65-b01, mixed mode)

However running echo $test yields a blank line.

回答1:

The reason that test="$(java -version)" prints the result to the terminal directly is that java -version outputs to standard error (stderr), not standard output (stdout).

Because there is no stdout output (which is what $(...) captures), $test is assigned an empty string.

The solution is to redirect standard error (stderr) to standard output (stdout).

version=$(java -version 2>&1)

来源：https://stackoverflow.com/questions/41213488/blank-variable-during-bash-command-substitution