# this increments x
x=1
echo "$((x++)), x is $x"
echo x is correct: $x

echo '========='

# but this doesn't change x outside the pipeline
x=1
echo "$((x++)), x is $x" | cat
echo x is still: $x

echo '========='

# same thing with non-arithmetic assignments ${name::=value}
# this works
x=1
echo "${x::=2}, x is $x"
echo x is correct: $x

echo '========='

# but this doesn't
x=1
echo "${x::=2}, x is $x" | cat
echo x is still: $x

echo '========='

x=1
echo $(echo "$((x++)), x is $x")
echo x is still: $x

echo '========='

x=1
<<<"$((x++)), x is $x"
echo x is still: $x

echo '========='

x=1
cat <<<"$((x++))"
echo x is still: $x

echo '========='

x=1
<<END
$((x++)), x is $x
END
echo x is still: $x

echo '========='

x=1
cat <<END
$((x++)), x is $x
END
echo x is still: $x