How to find multiple sub string patterns in a string in TCL - tcl

Question

I am trying to find multiple string patterns in a string in TCL. I cannot get the correct and optimized way to do that.
I have tried some code and it is not working
I have to find -h ,-he,-hel ,-help in the string -help
set args "-help"
set res1 [string first "-h" $args]
set res2 [ string first -he $args]
set res3 [string first -hel $args]
set res4 [string first "-help" $args"]
if { $res1 == -1 || $res2 || $res3 || $res4 } {
puts "\n string not found"
} else {
puts "\n string found"
}
how to use regexp here I am not sure , so need some inputs.
The expected output is

Answer 1

This is a case where using regexp is easier. (Asking if a string is a prefix of -help is a separate problem.) The trick here is to use ? and (…) (or rather (?:…) which is the non-capturing version) in the RE and you must use the -- option because the RE begins with a -:
if {[regexp -- {-h(?:e(?:lp?)?)?} $string]} {
puts "Found the string"
} else {
puts "Did not find the string"
}
If you want to know what string you actually found, add in a variable to pick up the overall match:
if {[regexp -- {-h(?:e(?:lp?)?)?} $string matched]} {
puts "Found the string '$matched'"
} else {
puts "Did not find the string"
}
If you instead want the indices where it matched, you need an extra option:
if {[regexp -indices -- {-h(?:e(?:lp?)?)?} $string match]} {
puts "Found the string at $match"
} else {
puts "Did not find the string"
}
If you were instead interested in whether the string was a prefix of -help, you instead should do:
if {[string equal -length [string length $string] $string "-help"]} {
puts "Found the string"
} else {
puts "Did not find the string"
}
Many uses of this sort of thing are actually doing command line parsing. In that case, the tcl::prefix command is very useful. For example, tcl::prefix match finds the entry in a list of options that a string is a unique prefix of and generates an error message when things are ambiguous or simply don't match; the result can be switched on easily:
set MY_OPTIONS {
-help
-someOtherOpt
}
switch [tcl::prefix match $MY_OPTIONS $string] {
-help {
puts "I have -help"
}
-someOtherOpt {
puts "I have -someOtherOpt"
}
}