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Jeroen W. Pluimers on .NET, C#, Delphi, databases, and personal interests

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Archive for May 30th, 2019

batch file – SHIFT doesn‚Äôt affect %* – Stack Overflow

Posted by jpluimers on 2019/05/30

Quoting the answer in full because it so tremendously useful [WayBack] batch file РSHIFT doesn’t affect %* РStack Overflow.

Especially the quoting/dequoting bits and the clever trick reconstructing %* into a batch file variable (minus double spaces).

Thanks so much James-K!

As you know, shift has no effect on %*, but you can construct a %* equivalent.

We’ll call the following¬†line.bat¬†:

@echo off
set line=%1
:loop
shift
if not "%1"=="" (
  set line=%line% %1
  goto :loop
)

echo   %%* = %*
echo line = %line%

If you type in the following command (Notice the double space between 3 and 4) :

line 1 2 3  4 bla dee dah

You will get the following output :

  %* = 1 2 3  4 bla dee dah
line = 1 2 3 4 bla dee dah

Note that %* retains multiple spaces, while using the %n notation does not.


Using something like this, you can allow your users to put their parameters in any order.

:loop
  :: Single variable parameters
  if "%1"=="something" set something=true
  :: Multi variable parameters 
  if "%~1"=="/source" shift & set source=%1
  shift
if not "%~1"=="" goto :loop

Notice that in the Multi-variable parameter statement I include one shift statement and one setstatement separated by an ampersand (&). The & tells the command processor that a separate command to be executed follows.


EDIT:

FYI: I recommend double quotes when checking the contents of variables.¬†Usually¬†you can use¬†anycharacter, and you don’t even need to use two because they are just there to insure that an empty variable does not cause an error. For instance, when¬†%1¬†is empty and you do¬†if not hello==%1 call :sub¬†the command processor will see this¬†if not hello== call :sub¬†and compare¬†hello¬†to¬†call¬†then try to execute¬†:sub, and throw an error. In that specific case¬†if not xhello==x%1 call :sub¬†is just as good as¬†if not "hello"=="%1" call :sub, because an empty¬†%1¬†will cause the command processor to see¬†if not xhello==x call :sub.

BUT using characters other than double-quotes will cause problems if the variable contains any special characters.

Using brackets as variable delimiters like (%1) can cause problems. For instance, the (special) piping characters don’t play nice inside brackets, and the escape character just seems to disappear, neither acting as a normal character, nor as the escape-character.

Also brackets are special characters in and of themselves designed to group and/or separate different lines of code and may not always act as anticipated.

Lastly, double quotes themselves are special characters specifically designed to surround other special characters, allowing them to act as normal characters. This is why you may see variables unquoted, then quoted again, like so.

set var="%~1"  & REM This sort of thing is used to insure that a variable is quoted.
                 REM %~1 unquotes %1 if it is already quoted, and leaves it alone if
                 REM %1 is not quoted.

set "var=%~1"  & REM This code assumes that `%1` contains special characters and
                 REM like before unquotes a quoted %1, but leaves the variable itself
                 REM unquoted. The double-quotes surrounding the variable and data
                 REM protects the command processor from any special characters that
                 REM exist in the data. Remember that anytime you reference `%var%`,
                 REM you will need to also surround the variable and data with
                 REM double-quotes.

A quick check for quotes is if exist %1 if %1==%~1 echo Unquoted.

–jeroen

Posted in Batch-Files, Development, Scripting, Software Development | Leave a Comment »

Testing for NULL and equality in practice

Posted by jpluimers on 2019/05/30

Great article: Testing for NULL and equality in practice [WayBack]

Most important table piece I learned:

 Testing (in)equality of A and B in different Firebird versions

Test type Firebird version
<= 1.5.x >= 2.0
Equality
A = B or A is null and B is null
A is not distinct from B
Inequality
A <> B
or A is null and B is not null
or A is not null and B is null
A is distinct from B

–jeroen

Posted in Database Development, Development, Firebird, SQL | Leave a Comment »

delphi – Sorting TDictionary by a key of Integer in ascending order – Stack Overflow

Posted by jpluimers on 2019/05/30

Great answer on [WayBack]¬†delphi – Sorting TDictionary by a key of Integer in ascending order – Stack Overflow¬†by J… comes down to this:

var
  LDictionary : TDictionary<Integer, string>;
  LArray : TArray<Integer>;
...
  LArray := LDictionary.Keys.ToArray();
  TArray.Sort<Integer>(LArray);

I was trying the wrong direction (functional approach like LArray := LDictionary.Keys.ToArray.Sort(); ), but the above procedural solution works.

Members used:

–jeroen

Posted in Delphi, Development, Software Development | 1 Comment »

 
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