Re: Bash – am I getting MAD here?

Jared Greenwald greenwaldjared at gmail.com
Wed Jul 27 20:01:11 UTC 2016


On Wed, Jul 27, 2016 at 2:48 PM, Johnny Rosenberg <gurus.knugum at gmail.com>
wrote:

> 2016-07-27 19:08 GMT+02:00 Jared Greenwald <greenwaldjared at gmail.com>:
>
>> The problem you have is that of namespace.  Even though you're declaring
>> the "FileName" variable within ToURI as a local, you're also declaring it
>> in the global context in the (now disabled) line.  It wouldn't necessarily
>> be a problem, but you're declaring FileName as an array in the global
>> context, so when you go to use it the ToURI context, bash basically doesn't
>> know what to do with an assignment to an array without a positional
>> reference.  Basically, you *could* override the global value in ToURI if
>> you wanted to by using a positional reference (eg [1]) or remove the
>> positional reference in the global context. My best suggestion would be to
>> just change the local variable name in ToURI to something that doesn't
>> collide with the global namespace.
>>
>
> I think I see what you mean.
> About the array thing, I actually found later that replacing *FileName[1]=$(basename
> "${File[1]}") with **FileName=$(basename "${File[1]}") *worked too, and
> that was also my first solution, giving a slightly slower script, not
> noticeable though.
>

Without the context of the larger script, it's hard to say what might be
causing the issue.  The small snippet doesn't really justify to me the use
of an array, but the larger context might.  In the past, I've only really
used arrays in bash when it was absolutely necessary since there are plenty
of other ways to skin that cat.


>
> Having another look at my ToURI function, I'm also wondering if ”*export
> local*” is meaningful. Sounds like a contradiction… But I need the export
> for the perl thing at the end of the function, I don't think it will work
> otherwise.
>

I doubt that it has any implication.  The "export" is really the only thing
you needed there I think and as someone else pointed out, you can just do
it in one line.  Cleaner and more concise.


>
> However, I replaced FileName in the ToURI function with InputFile and it
> seems to work now.
>

Yea, really anything would have worked there as long as it wasn't FileName.


> Thank you very much for your input. I guess I should have understood this
> myself, but I'm good at other things… :P
>

I'm certainly no expert in bash.  As shown by the fact that others pointed
out things I didn't see.  The only way to learn and make better code is to
try what you know and then get input and advice from others.


>
>
> Kind regards
>
> Johnny Rosenberg
>
>
>
>>
>> On Wed, Jul 27, 2016 at 11:59 AM, Johnny Rosenberg <
>> gurus.knugum at gmail.com> wrote:
>>
>>> Hi!
>>>
>>> I really really don't understand what's going on here. I have a rather
>>> big script and there is something that doesn't work properly, and after
>>> hours of debugging, I found the problem line.
>>>
>>> Since the script is very big, 19 files at the moment, I made a shorter
>>> example that has exactly the same problem. Here it is:
>>>
>>> *#!/bin/bash*
>>>
>>> *FullPathName() {*
>>> * # Declare local variables*
>>> * local Path="$1"*
>>> * if [[ ${Path:0:1} != / ]]; then # Relative path.*
>>> * echo "${PWD}/${Path}"*
>>> * else # Absolute path.*
>>> * echo "${Path}"*
>>> * fi*
>>> *}*
>>>
>>> *ToURI () {*
>>> * # Declare local variables.*
>>> * export local FileName="$1"*
>>> * perl -MURI::file -e 'print URI::file->new($ENV{'FileName'})."\n"'*
>>> *}*
>>>
>>> *File[1]=$(FullPathName "${1}")*
>>> *FileName[1]=$(basename "${File[1]}")*
>>>
>>> *SelectedProject="Projekt Johnny Guitar"*
>>> *RemoteRootFolder="http://web.comhem.se/something
>>> <http://web.comhem.se/something>"*
>>> *RemoteProjectFolder="${RemoteRootFolder}/"$(ToURI "${SelectedProject}")*
>>>
>>> *echo "${RemoteProjectFolder}"*
>>>
>>> as you can see, the *File* and *FileName* variables are not used for
>>> anything in this example, but they still illustrate the problem. I named
>>> the file *TEST.sh*, put it in my *~/bin* folder which is included in my
>>> *PATH* environment variable, so I will run this test with a random file
>>> as an argument.
>>>
>>> Now, let's run this:
>>> *~$ TEST.sh .netrc*
>>> *http://web.comhem.se/something/ <http://web.comhem.se/something/>*
>>> *~$ *
>>> Obviously, *$(ToURI "${SelectedProject}" *didn't do anything, but why?
>>>
>>> So, as I said, after hours of debugging, I came up with this:
>>> *#!/bin/bash*
>>>
>>> *FullPathName() {*
>>> * # Declare local variables*
>>> * local Path="$1"*
>>> * if [[ ${Path:0:1} != / ]]; then # Relative path.*
>>> * echo "${PWD}/${Path}"*
>>> * else # Absolute path.*
>>> * echo "${Path}"*
>>> * fi*
>>> *}*
>>>
>>> *ToURI () {*
>>> * # Declare local variables.*
>>> * export local FileName="$1"*
>>> * perl -MURI::file -e 'print URI::file->new($ENV{'FileName'})."\n"'*
>>> *}*
>>>
>>> *File[1]=$(FullPathName "${1}")*
>>> *# FileName[1]=$(basename "${File[1]}") ############## Disabled line
>>> ###############*
>>>
>>> *SelectedProject="Projekt Johnny Guitar"*
>>> *RemoteRootFolder="http://web.comhem.se/something
>>> <http://web.comhem.se/something>"*
>>> *RemoteProjectFolder="${RemoteRootFolder}/"$(ToURI "${SelectedProject}")*
>>>
>>> *echo "${RemoteProjectFolder}"*
>>>
>>> So, the only difference is that I disabled the line *FileName[1]=$(basename
>>> "${File[1]}")*.
>>>
>>> Now, let's try again:
>>> *~$ TEST.sh .netrc*
>>> *http://web.comhem.se/something/Projekt%20Johnny%20Guitar
>>> <http://web.comhem.se/something/Projekt%20Johnny%20Guitar>*
>>> *~$ *
>>>
>>> So, suddenly it works, but WHY?
>>> I early suspected *basename*, but in the original script there are
>>> several *basename* statements, but they don't mess anything up.
>>>
>>>
>>> Seriously, what is going on here?
>>>
>>> *~$ bash --version | grep release*
>>> *GNU bash, version 4.3.11(1)-release (i686-pc-linux-gnu)*
>>> *~$*
>>>
>>>
>>>
>>> *Any help is greatly appreciated, since this is a real showstopper for
>>> me at the moment.*
>>>
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>>>
>>
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