Declare a here-string containing variables outside of a loop

Question

I would like to declare a here-string outside of a loop use that string in the loop where the variables get resolved.

My ideal scenario would look like below. This doesn't work as Powershell evaluates the string one time before entering the loop instead of each time inside the loop _{kind of obvious but bitten by it nevertheless.}

$number = "Number $($_)"
1..2 | % { $number }

I know I can use one of these solutions

1..2 | % { "Number $($_)" }

$number = "Number {0}"
1..2 | % { $number -f $_ }

$number = "Number <replace>"
1..2 | % { $number -replace "<replace>", "$_" }

but they have drawbacks I'd like to avoid

Due to the size of the string, declaring it inside the loop obfuscates the logic of the loop making the code less readable.
The formatting solution is too easy to get wrong when many variables are involved.
In the replace solution it's easier to match what get's replaced by what variable but I would have to chain many replace commands.

Edit

Rereading my own question makes it obvious that the actual use case is missing from the question.
_{Note that ultimately I ended up choosing the formatting option}

Following would declare the template with some variables that need replacing in a loop

    $sqltemplate = @"
        SELECT  aud.dpt_mov_hex||aud.dpt_ref||aud.can_typ||TO_CHAR(aud.dte_aud-1,'YYYYMMDD')||'000001' transaction_id,
                acc.dos_nbr contract_id, acc.pay_acc_nbr account_id, 
                CASE WHEN NULL IS NULL THEN unt.nam_unt ELSE unt.nam_unt||'<'||NULL ||'>' END product_id,
                aud.dpt_ref, aud.dpt_mov_hex, aud.dpt_mov_dte uitwerkingsdatum, 
                CASE WHEN can_typ = 0 THEN 'VZ'||aud.dpt_mov_ven_typ ELSE 'VZ'||aud.dpt_mov_ven_typ||'-CR' END transactietype,
                aud.dpt_mov_amt_eur bedrag_in_eur, aud.dte_cnv, aud.dpt_mov_fix_eur, aud.dpt_mov_con_inc, aud.dpt_mov_amt_sgn bedrag_teken,
                aud.dpt_mov_amt_unt bedrag_in_units, aud.dpt_mov_amt_rte, aud.dpt_mov_amt_val_pre, aud.dpt_mov_amt_val_aft,
                aud.dpt_mov_amt_ioc, aud.dte_exe verwerkingsdatum, aud.exe_mng, aud.cmt, aud.trn_nbr, aud.dte_aud datum_aanlevering, aud.can_typ
        FROM    lfe_dpt_mov_aud aud, vnv_isr_pay_acc acc, vnv_bel_unt unt
        WHERE   aud.dte_aud >= TO_DATE('$((Get-Date).ToString('dd.MM.yyyy'))', 'DD.MM.YYYY')
                AND aud.dpt_ref = '{0}'
                AND acc.pay_acc_nbr = '{1}'
                AND unt.inv_unt = '{2}'
        UNION
        SELECT  aud.dpt_mov_hex||aud.dpt_ref||aud.can_typ||TO_CHAR(aud.dte_aud-1,'YYYYMMDD')||'000001' transaction_id,
                acc.dos_nbr contract_id, acc.pay_acc_nbr account_id, 
                CASE WHEN itr_rte IS NULL THEN unt.nam_unt ELSE unt.nam_unt||'<'||itr_rte ||'>' END product_id,
                aud.dpt_ref, aud.dpt_mov_hex, aud.dpt_mov_dte uitwerkingsdatum,
                CASE WHEN can_typ = 0 THEN 'VZ'||aud.dpt_mov_ven_typ ELSE 'VZ'||aud.dpt_mov_ven_typ||'-CR' END transactietype, 
                aud.dpt_mov_amt_eur bedrag_in_eur, aud.dte_cnv, aud.dpt_mov_fix_eur, aud.dpt_mov_con_inc, aud.dpt_mov_amt_sgn bedrag_teken,
                aud.dpt_mov_amt_unt bedrag_in_units, aud.dpt_mov_amt_rte, aud.dpt_mov_amt_val_pre, aud.dpt_mov_amt_val_aft,
                aud.dpt_mov_amt_ioc, aud.dte_exe verwerkingsdatum, aud.exe_mng, aud.cmt, aud.trn_nbr, aud.dte_aud datum_aanlevering, aud.can_typ
        FROM    lfe_dpt_mov_aud aud, vnv_dpt dpt, vnv_isr_pay_acc acc, vnv_bel_unt unt
        WHERE   aud.dpt_ref = dpt.dpt_ref
                AND dpt.pay_acc = acc.pay_acc_nbr
                AND dpt.inv_unt = unt.inv_unt
                AND aud.dte_aud >= TO_DATE('$((Get-Date).ToString('dd.MM.yyyy'))', 'DD.MM.YYYY')
                AND acc.pay_acc_nbr = '{1}'
                AND unt.inv_unt = '{2}'
        UNION
"@

and this template would get used in a statement such as this

_{$rolledbackMatchs is an array of custom object containing the three properties: dtp_ref, pay_acc_nbr and inv_unt.}

$rolledbackMatches | ForEach-Object { $sqltemplate -f $_.dpt_ref, $_.pay_acc_nbr, $_.inv_unt }

score 2 · Accepted Answer · answered Sep 12 '18 at 13:42

Couple of approaches come to mind:

dot source here-string assignment from a separate file:

# loop.variables.ps1
$myVar = @"
Stuff going on with $_ in here
"@

and then in the loop itself:

1..2 | % { . .\loop.variables.ps1; <# do stuff with $myVar here #> }

Manually invoke string expansion:

$hereString = @'
Stuff (not yet) going on with $_ in here
'@
1..2 | % { $myVar = $ExecutionContext.InvokeCommand.ExpandString($hereString) }

Wrap it in a scriptblock

(as suggested by PetSerAl)

$stringBlock = {
@"
Stuff going on with $_ in here
"@
}
1..2 | % { $myVar = &$stringBlock}

The ExpandString solution was what I have seen before and couldn't remember. The scriptblock solution is quit nice, pondering over what to use. Thank you (both) — Lieven Keersmaekers, Sep 12 '18 at 14:15

score 1 · Answer 2 · answered Sep 12 '18 at 13:35

1

I'm struggling to understand what you're trying to achieve here.

For a start you never define a here-string you just define $number as a string

A here-string would look like this

$number = @"
Number 4
"@

if all you're trying to do is push a number into a string try this

foreach ($number in (1..3)){
  "Number $number"
}

which is close to your desired option and less ambiguous

answered Sep 12 '18 at 13:35

Richard Siddaway

451
2
4

you are right about this not being a here-string. That part got lost when making up the examples but the gist of it remains the same. Your solution works but it's not what I'm after, tx. – Lieven Keersmaekers Sep 12 '18 at 14:01

Declare a here-string containing variables outside of a loop

2 Answers2

dot source here-string assignment from a separate file:

Manually invoke string expansion:

Wrap it in a scriptblock