On 3/27/19 9:44 AM, Roger Koehler via blfs-dev wrote:
On Wed, Mar 27, 2019, 6:52 AM Pierre Labastie via blfs-dev
<[email protected]
<mailto:[email protected]>> wrote:
Hi,
When making scripts from the book (either by copy/paste
or some use of xsltproc), the generated scripts have `&&' at
the end of each line. It allows to not execute the following
instructions if one instructions fail, but it defeats the use of
"set -e". From the bash man page under the set builtin, for
option -e (emphasis by me):
------------
Exit immediately if a pipeline (which may consist of a
single simple command), a list, or a compound command
(see SHELL GRAMMAR above), exits with a non-zero status.
*The shell does not exit if the command that fails is
part of the command list immediately following a while
or until keyword, part of the test following the if or
elif reserved words, part of any command executed in a
&& or || list except the command following the final &&
or ||, any command in a pipeline but the last, or if the
command's return value is being inverted with !.*[...]
------------
In short, with a construct like:
----
set -e
instruction A &&
instruction B &&
instruction C
----
The script does not exit if either instruction A or instruction B fails,
but the following instructions are not executed... This may lead to
a script completing successfully, while the package was in fact not
installed, or only partially installed or compiled!
So why do we use those `&&' in the book???
I've tried to automatically remove the `&&' in jhalfs, but it is not
possible, because sometimes, the `... && ...' construct really
really means
if ...; then ...
There could be a solution: ask devs not to use `... && ...' when
they mean
if ...; then ...
Another is to not have `&&' at the end of line. Actually, what would we
lose?
For me, it makes it easy to see which commands go together when editing
the jhalfs-generated scripts. For example, to remove the generation of
API documentation when I don't have the necessary tools installed.
However, I would gladly forego that luxury for the peace of mind in
knowing that when a build completes successfully, it actually installed
everything.
I think most users just copy/paste the instructions instead of
scripting. In that case using && makes the instructions fail on the
problematic instruction instead of continuing to the rest of the
commands in the block. In places like xorg-libs where we create a
script-like environment using 'bash -e', we do not use &&.
Personally I wrap my scripts in
{
a &&
b
}
if [ $PIPESTATUS -ne 0 ]; then exit 1; fi;
-- Bruce
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