On Sat, Aug 14, 2021, at 6:59 PM, George Nachman wrote:
> Description:
> Defining an alias named `done` breaks parsing a for loop that does not have
> an `in word` clause.
>
>
> Repeat-By:
>
> Run the following script. It fails with this error:
>
> myscript.bash: line 7: syntax error near unexpected token `done'
> myscript.bash: line 7: ` done'
>
>
> #!/bin/bash
>
> alias done=""
>
> f() {
> for var; do
> done
> }
The 'alias' command is irrelevant because aliases are not expanded
in noninteractive shells by default. The absence of 'in X' is also
irrelevant. The problem is that there cannot be *nothing* between
'do' and 'done'. (I'll let someone more patient relate this to the
formal grammar, if they're so inclined.)
% bash --version | head -n 1
GNU bash, version 5.1.8(1)-release (x86_64-apple-darwin18.7.0)
% cat /tmp/myscript1.bash
f() {
for var in a b c; do
done
}
% bash /tmp/myscript1.bash
/tmp/myscript1.bash: line 3: syntax error near unexpected token `done'
/tmp/myscript1.bash: line 3: ` done'
You *can* force alias expansion by setting expand_aliases, in which
case you get a different error.
% cat /tmp/myscript2.bash
alias done=''
f() {
for var in a b c; do
done
}
% bash -O expand_aliases /tmp/myscript2.bash
/tmp/myscript2.bash: line 6: syntax error near unexpected token `}'
/tmp/myscript2.bash: line 6: `}'
This is the same error you'd get if you simply omitted 'done'
entirely, which should make sense.
> Fix:
> `done` should not be considered a simple command in the context where it
> would terminate a for loop.
POSIX mode does disable alias expansion in that situation (see
<https://www.gnu.org/software/bash/manual/html_node/Bash-POSIX-Mode.html>,
item 7). Perhaps the default behavior is for backward compatibility?
% bash --posix /tmp/myscript2.bash
/tmp/myscript2.bash: line 5: syntax error near unexpected token `done'
/tmp/myscript2.bash: line 5: ` done'
--
vq
