So, perhaps you could add additional variable input & negative index numbers to your list of possible enhacements to %T.
Consider, too, returning multiple lines from the text file (ie 2-4, 0=all) for post-processing with regex (assuming the regex engine works on multi-line text strings, which I haven't tested)

Thanks again for the help.
I'm particularly pleased, now have an easy way to rename path from file names.

I noticed you seemed to start your DOS commands manually via a extern "cmd" command.
Have you tried using the Siren's "Tools" feature ?
I have made some tests and it seems to work correctly.
For example to create the "numfiles.txt" files I added a new entry in "Tools" :
Name : Create numfiles.txt
Command : cmd /C \"dir /b /a-d \"%f\" | find  /c /v \"\" > \"%f\\numfiles.txt\"\"

Just a reminder : the "tools" are executed on highlighted files, not the selected ones.

Regards

But you could had used SORT
for /D %i in (*) do @(sort /R "%i\dirfiles.txt" /O "%i\dirfiles.txt")

But DIR has also a reverse switch for the /O operator: -

I had two additional ideas:
1. prefix the temp file name  with zzz or 000 (zero) respective to sort them out
of the way, to be NOT the first / last file in folder.
2. add a (s///) modifier to the %T variable to remove that temp file name, if it is the only one in folder.

So I have testet this:

To get first file from folder (Note the zzz prefix) :
step 1:for /D %i in (*) do @(dir /b /a-d /on "%i" > "%i\zzzdirfiles.txt")
step 2: %T{%fa(s/$/\\zzzdirfiles.txt/),1}(s/zzzdirfiles.txt//);%b

To get last file from folder (Note the /o-n DIR switch and the 000 prefix):
step 1:for /D %i in (*) do @(dir /b /a-d /o-n "%i" > "%i\000dirfiles.txt")
step 2: %T{%fa(s/$/\\000dirfiles.txt/),1}(s/000dirfiles.txt//);%b

Of course we would use '000' and 'zzz' without extension as temp file name only, to make typing easier 

HTH? 

(At least 60 seconds have to pass between posts. Please wait a while and try posting again.)

Example: I have a bunch of folders with non-descript names but the 1st file in each folder is a cover with a name in the form of "Date - Artist - Album.jpg"

step 1: for /D %i in (*) do @(dir /b /a-d /on "%i" > "%i\dirfiles.txt")
step 2: %T{%fa(s/$/\\dirfiles.txt/),1};%b
step 3: for /D %i in (*) do @(del "%i\dirfiles.txt")

Voila!

One thing I noticed playing around with this. If the file I want to use as folder name is the last file, then the form:
%T{%fa(s/$/\\dirfiles.txt/),-1};%b
Doesn't seem to work.

step 1, run from cmd prompt, creates numfiles.txt:
   for /D %i in (*) do @(dir /b /a-d "%i" | find  /c /v "" > "%i\numfiles.txt")

step 2, run in siren, rename Filename >> Filename (xN) where N = number of files.
Note: Have to subtract 1 for numfiles.txt or 2 if thumbs.db exists
  %b - %T{%fa(s/$/\\numfiles.txt/),1};%b[1,-1] (x%N{1,-1,-1})

step 3, run from cmd prompt, deletes numfiles.txt
  for /D %i in (*) do @(del "%i\numfiles.txt")

BTW: Sorry about misplacing the post. Yes, please, move the thread to proper place.

Just mention that trick to 'read files relative to folders' in the help file.
Read always first line from each file:
%T{  %fa(s/$/\\Text.txt/) , 1 }

Additional mention the way to 'read one file from Sirens' home folder':
%Pe the path to Siren's executable file 
Read lines from a single file, but relative to file selection in Siren list view:
%T{  %Pe(s/$/\\Text.txt/)     }
Of course, if you do not need this portable, relative path, you can also use the absolute path, like e.g.
%T{  "C:\\Tools\\SirenV3\\Text.txt"     }

- - -
BTW:
the relative path form works also for me:
%T{ %f(s///) ,1}
and
%T{ %b(s///) ,1}
instead of
%T{ %fa(s///) ,1}

Great solution, Rémi!

- - -

%b_(%T{%fa(s/$/\\_SirenNumFiles.txt/),1} files)

works for me on Siren v3.

Even with spaces in  path.

- - -

Examples (some folders without '_SirenNumFiles.txt'):

Current name    New name    Sel    Type                   
Accents    Accents_(6 files)    004 Directory
Add-fitting-Zeros    Add-fitting-Zeros_( files)    005 Directory
AddSerialize inbetween    AddSerialize inbetween_(2 files)    006    Directory
AddSpacebetween Upper case Letter    AddSpacebetween Upper case Letter_(1 files)    007    Directory   
AddSpacebetweenLetterAndDigitsOrSymbol    AddSpacebetweenLetterAndDigitsOrSymbol_(4 files) 008 Directory
b    b_( files)    009 Directory

- - -

Explanation:

%b_ >>> origin base name, without extension.

( >>> A literal '(' sign.

%T{%fa(s/$/\\_SirenNumFiles.txt/),1} >>>
>>> %T{file path,1} expression
>>> plus %fa expression as file path
>>> with an additional '(s///)'- RegEx search&replace on that %fa expression.

%fa(s/$/\\_SirenNumFiles.txt/)
>>> match the end of the value of %fa
>>> and add an (here regex escaped) backslash
>>> plus a literal string (here: '_SirenNumFiles.txt')

files)  >>> literal ' files)' sings.

Fine!

Thanks Rémi :thumpsup:

There are different ways to get what you want.
The simplest seems to be the regular expression modifier.
For example : %b_%T{%fa(s/$/\\numfiles.txt/),1}

Here, the metacharacter '$' (regular expression standard) represents the end the string.
In our case the end of "%fa".
'$' is replaced by "\numfiles.txt" which is equivalent to concatenate the two strings.

I have already thought about expanding the expression syntax to allow a more natural way
to achieve this but I haven't found the right solution yet.
Do not hesitate to give your ideas.

One remark : you posted in the "Siren 1 or 2" part of this forum but this expression
won't work with these old versions.
Maybe should I move this post to the "Siren 3" section. Ok ?

Regards

And here is such a AHK-script for Siren v3 for your purpose:

#SingleInstance, force
;1) Open Siren v3 and select the wanted folders.
;2) Switch to WinExplorer and execute this script with installed AutoHotkey application
;3) Switch back to Siren and watch what happens....
;================================================
;;;; THE STEPS....
;IF Siren gets the focus:
WinWaitActive, ahk_class wxWindowNR 
;================================================
  ;Enter Siren expression: %fa to get full path of selected folder
  ControlSetText, Edit1,`%fa, Siren
  ;Execute Siren command Ctrl+P
  Send ^p
  ClipWait 
  ;For each copied line (folder name) do:
  Loop parse, clipboard, `n , `r
{
        ;Skip header line:
        if A_Index = 1
            continue

       myLine :=A_LoopField 
       Loop, parse, myLine, %A_Tab%
       {
            ;myLine is tab-delimited.
            ;Get New Name field (2th field):
            if(A_Index = 2){
                vFolder := A_LoopField
                
                ;Read in the file content:
                vFile = %vFolder%\SirenNumfiles.txt
                if (FileExist(vFile)){
                    FileReadLine, vOutputVar,%vFile%, 1
                    myOut = %myOut%%vOutputVar%`r`n
                }
            }
       }
  }
;================================================
;OUTPUT:
;MsgBox OUT:`r`n%myOut%
clipboard := myOut   
WinActivate,  ahk_class wxWindowNR
;Enter Siren expression: "%b_(%C files)" for new name of selected folder:
ControlSetText, Edit1,`%b_(`%C files), Siren
ExitApp
;================================================

Maybe it would be possible for Rémi to enhance %T{}
to allow calculating sub-expressions like:      >>> %T{  (%pa

EDIT:
was cut...

>>> %T{  (%pa"Numfiles.txt")  } <<<

Siren doesn't have a file count variable so I thought of using a textfile to save the file count & came up with this to generate the text file from the cmd prompt:
for /D %i in (*) do @(dir /b /a-d "%i" | find  /c /v "" > "%i\numfiles.txt")

So now I have numfiles.txt in each of the directories; I thought I could use %T to rename:

%b (x%T{"%fa\\numfiles.txt",1})

Alas %T appears not to accept variables in the "f" parameter.

Also thought of continuing at the command prompt but am stumped trying to get REN to accept variable input.

Ideas? Suggestions?