need help in tcl command usage for regsub - regex

Question

I am new learner for tcl. I have some issue as below when using regsub. Consider the following scenario:
set test1 [list prefix_abc_3 abc_1 abc_2 AAA_0]
set test2 abc
regsub -all ${test2}_[1-9] $test1 [list] test1
I expected $test1 output is [prefix_abc_3 AAA_0]
However regsub has also removed the partial matched string which is prefix_abc_3. Does anyone here have any idea on how to regsub the exact words only in a list?
I tried to find solution via net but could not get any clue/hints. Appreciate if someone here can help me.

Answer 1

\m and \M in regexps match the beginning and end of a word respectively. But you don't have a string of words in test1, but a list of elements, and sometimes there's a difference so don't mix the two. regsub only handles strings while lsearch works with lists:
set test1 [list prefix_abc_3 abc_1 abc_2 AAA_0]
set test2 abc
set test1 [lsearch -all -inline -not -regexp $test1 "^${test2}_\[1-9\]\$"]
If the pattern is that simple, you can use the -glob option (the default) instead of -regexp and maybe save some processor time.

Answer 2

What exactly did you execute?
When I type the commands above into tclsh, it displays an error -
% set test1 [list prefix_abc_3 abc_1 abc_2 AAA_0]
prefix_abc_3 abc_1 abc_2 AAA_0
% set test2 abc
abc
% regsub -all ${test2}_[1-9] [list] test1
invalid command name "1-9"
I'm unsure what you are trying to do. You start by inisitalising test1 as a list. You then treat it as a string by passing it to regsub. This is a completely legal thing to do, but may indicate that you are confused by something. Are you trying to test your substitution by applying it four times, to each of prefix_abc_3, abc_1, abc_2 and AAA_0? You can certainly do that the way you are, but a more natural way would be to do
foreach test $test1 {
regsub $pattern $test [list] testResult
puts stdout $testResult
}
Then again, what are you trying to achieve with your substitution? It looks as though your are trying to replace the stringabc with a null string, i.e. remove it altogether. Passing [list] as a null string is perfectly valid, but again may indicate confusion between lists and strings.
To achieve the result you want, all you need to do is add a leading space to your pattern, pass a space as the substitution string and escape the square brackets, i.e.
regsub -all " ${test2}_\[-9\]" $test1 " " test1
but I suspect that this is a made-up example and you're really trying to do something slightly different.
Edit
To obtain a list that contains just those list entries that don't exactly match your pattern, I suggest
proc removeExactMatches {input} {
set result [list]; # Initialise the result list
foreach inputElement $input {
if {![regexp {^abc_[0-9]$} $inputElement]} {
lappend result $inputElement
}
}
return $result
}
set test1 [removeExactMatches [list prefix_abc_3 abc_1 abc_2 AAA_0]]
Notes:
i) I don't use regsub at all.
ii) Although it's safe and legal to switch around between lists and strings, it all takes time and it obscures what I'm tryng to do, so I avoid it wherever possible. You seem to have a list of strings and you want to remove some of them, so that's what I use in my suggested solution. The regular expression commands in Tcl handle strings so I pass them strings.
iii) To ensure that the list elements match exactly, I anchor the pattern to the start and end of the string that I'm matching against using ^ and $.
iv) To prevent the interpreter from recognising the [1-9] in the regular expression pattern and trying to execute a (non-existant) command 1-9, I enclose the whole pattern string within curly brackets.
v) For greater generality, I might want to pass the pattern to the proc as well as the input list (of strings), in that case, I'd do
proc removeExactMatches {inputPattern input} {
.
.
.
set pattern "^"
append pattern $inputPattern
append pattern "\$"
.
.
.
if {![regub $pattern $inputElement]} {
.
.
.
}
set test1 [removeExactMatches {abc_[1-9]} {prefix_abc_3 abc_1 abc_2 AAA_0}]
to minimise the number of characters that had to be escaped. (Actually I probably wouldn't use the quotation marks for the start and end anchors within the proc - they aren't really needed and I'm a lazy typist!)
Looking at your original question, it seems that you might want to vary only the abc part of the pattern, in which case you might want to just pass that to your proc and append the _[0-9] as well as the anchors within it - don't forget to escape the square brackets or use curly brackets if you go down this route.