A continue or break from a subshell inside a loop no longer works.

Bug #1975866 reported by Johnny Klonaris
6
This bug affects 1 person
Affects Status Importance Assigned to Milestone
ubuntu-docs (Ubuntu)
Invalid
Undecided
Unassigned

Bug Description

The following code works in bash on any number of Linux distros, including
CentOS 6.10 - 7.8 and Ubuntu 14.04 - 18.04.

#!/bin/bash
#
# Test for continue from subshell issue...
#
echo SHELL is $SHELL
for i in $(seq 5)
do
    (
    echo loop $i
    if [[ $i == 2 ]] ; then
        echo i = $i - continue
        continue
    fi

    if [[ $i == 4 ]] ; then
        echo i = $i - exit
        exit 1
    fi
    echo Loop $i subshell end
    )
    rc=$?
    echo Loop $i rc $rc
done

--
The output on all of those machines is:

SHELL is /bin/bash
loop 1
Loop 1 subshell end
Loop 1 rc 0
loop 2
i = 2 - continue
Loop 2 rc 0
loop 3
Loop 3 subshell end
Loop 3 rc 0
loop 4
i = 4 - exit
Loop 4 rc 1
loop 5
Loop 5 subshell end
Loop 5 rc 0

---
On a Ubuntu 20.04 machine:

SHELL is /bin/bash
loop 1
Loop 1 subshell end
Loop 1 rc 0
loop 2
i = 2 - continue
packages/tmp/looptest: line 14: continue: only meaningful in a `for', `while',
or `until' loop
Loop 2 subshell end
Loop 2 rc 0
loop 3
Loop 3 subshell end
Loop 3 rc 0
loop 4
i = 4 - exit
Loop 4 rc 1
loop 5
Loop 5 subshell end
Loop 5 rc 0

--
If I change the shebang to: #!/bin/sh
the behavior is the same as the first example - except - on our machines, we
specifically link /bin/sh to bash:

$ ls -l /bin/sh
lrwxrwxrwx 1 root root 9 May 12 22:04 /bin/sh -> /bin/bash

Which seems just... weird.

This behavior seems to have started after a recent update to Ubuntu 20.04.

I realize that the argument can be made the new behavior is more technically
correct, but using a subshell to isolate vars between loops can be very helpful
and the fact that this has worked until now is concerning.

Revision history for this message
Gunnar Hjalmarsson (gunnarhj) wrote :

This is not a bug about the Ubuntu Desktop Guide, so closing.

I would recommend you to show your observation at Ask Ubuntu. If you then conclude that it's a bug, please report it against the bash package.

Changed in ubuntu-docs (Ubuntu):
status: New → Invalid
Revision history for this message
Johnny Klonaris (jklonaris) wrote :

Gunnar - thanks. I realized that I might have filed it in the wrong place - my apologies.

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