Regex expected to match one letter matches whole word [duplicate] - regex

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Regular expression pipe confusion
(5 answers)
Closed 5 months ago.
I have this expression in a switch statement for a script controlpanel
$ctrlinpt=read-host ">>>"
switch -regex ( $ctrlinpt )
{
<#1#>'^\w{2,}|\d{2,}$' { do this }
<#2#>'^c{1}|C{1}$' { do that }
<#3#>'^l{1}|L{1}$' { do somethign else }
<#4#>'^s{1}|S{1}$' { take a break }
<#5#>'^exit$'{ go home }
}
The first condition should match any input with more than one character and it does. However , if the input starts with one of the letters in the other conditions, it also matches their cases
for example
"Task1" matches only case 1
"Legacy" matches case 1 and case 3
"supper" matches case 1 and case 4
I expect cases 2,3, and 4 to only match an input of exactly the one character stated. What am I doing wrong?

Answer 1

The pattern '^l{1}|L{1}$' is interpreted as "a string starting with l OR a string ending with L" - and since PowerShell does case-insensitive comparisons by default, "a string starting with l" perfectly describes Legacy.
To fix this, you can nest the alternation in a grouping construct:
^(?:l{1}|L{1})$
... or use a character class:
^[lL]$
... or, since the matches are case-insensitive by default anyway, simply match on a single character literal:
^l$
Thus, your switch becomes:
$ctrlinpt = read-host ">>>"
switch -regex ( $ctrlinpt ) {
'^(?:\w{2,}|\d{2,})$' { do this }
'^c$' { do that }
'^l$' { do somethign else }
'^s$' { take a break }
'^exit$' { go home }
}
Since regex isn't really required for the last 4 cases, I'd suggest removing the -regex mode switch altogether and use a predicate for the first case instead:
$ctrlinpt = read-host ">>>"
switch ( $ctrlinpt ) {
{ $_ -match '^(?:\w{2,}|\d{2,})$' } { do this }
'c' { do that }
'l' { do somethign else }
's' { take a break }
'exit' { go home }
}