bash 4.2 / 4.3: Different behavior in C-style loop

Question

bash 4.2 show the assumed correct behavior in a C-style for loop:

me@server:/some/dir# TIMES=30; for (( n=0; n<$(shuf -i ${TIMES}-$(expr ${TIMES} + 20) -n 1); n++ )); do echo $n; done
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me@server:/some/dir# bash --version
GNU bash, Version 4.2.25(1)-release (x86_64-pc-linux-gnu)
(...)
me@server:/some/dir#

The same under bash 4.3 throws an error:

me@server:/some/dir# TIMES=30; for (( n=0; n<$(shuf -i ${TIMES}-$(expr ${TIMES} + 20) -n 1); n++ )); do echo $n; done
-bash: syntax error near unexpected token `newline'
me@server:/some/dir# bash --version
GNU bash, Version 4.3.30(1)-release (x86_64-pc-linux-gnu)
(...)

Yet the part to find a random number between ${TIMES} and ${TIMES}+20 works:

me@server:/some/dir# shuf -i 20-50 -n 1
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me@server:/some/dir#

So does inserting the numeral directly instead of $()-subshell'ing it:

me@server:/some/dir# TIMES=30; for (( n=0; n<26; n++ )); do echo $n; done
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me@server:/some/dir#

What's going on here? Any ideas why the subshell is not executed correctly under bash 4.3?

Answer 1

If you replace $(expr with $((, it starts to work:

TIMES=30
for (( n=0; n < $(shuf -i $TIMES-$((TIMES + 20)) -n 1); n++ )) ; do
    echo $n
done