Tcl, if not not working - tcl

Question

I'm trying to do a If not on a string match with Tcl. However, when I expect it not to match, it seems to be matching because when it shouldn't match it continues to "I don't want it to do this". Hope this makes sense. Inside the log.text file, it should contain, "This is a String."
set var1 "String"
set file [open "log.text" r]
while {[gets $file data] != -1} {
if {![string match *[string toupper $var1]* [string toupper $data]]} {
*I don't want it to do this
}
}

Answer 1

Your code appears to work fine:
$ cat log.text
This is a String
this line does not match
$ tclsh <<'END'
set var1 "String"
set file [open "log.text" r]
while {[gets $file data] != -1} {
if {![string match -nocase *$var1* $data]} {
puts "$data: does not match $var1"
}
}
END
outputs
this line does not match: does not match String
Ah, now you have clearly stated what you want: does the string exist in the file, yes or no. Here are some ways to accomplish that:
read the entire file, and string match against that.
set file [open log.text r]
set contents [read -nonewline $file]
close $file
set pattern_exists [string match -nocase *$var1* $contents]
if {$pattern_exists} {puts "$var1 found in file"}
read the file line-by-line until the pattern is found
set pattern_exists false
set file [open log.text r]
while {[gets $file line] != -1} {
if {[string match -nocase *$var1* $line]} {
set pattern_exists true
break
}
}
close $file
if {$pattern_exists} {puts "$var1 found in file"}
call out to grep to do the heavy lifting: grep exits with non-zero status when the pattern is not found, and exec thinks a non-zero exit status is an exception (see https://tcl.tk/man/tcl8.6/TclCmd/exec.htm#M27)
try {
exec grep -qi $var1 log.text
set pattern_exists true
} on error {e} {
set pattern_exists false
}
if {$pattern_exists} {puts "$var1 found in file"}

Answer 2

The code as you wrote it works… but I'm guessing it is a proxy for something else. If you are looking to see if an arbitrary string exists as a substring of a line, you are better off using string first instead of string match, since the latter has a few metacharacters (especially [ and ], which denote a set of characters) that can cause problems if you're not expecting them.
Try:
if {[string first [string toupper $var1] [string toupper $data]] >= 0} {
# The substring was there...
}
Alternatively, apply relevant backslash quoting when building your search pattern (possibly with string map) or use regexp, which has a useful find-a-literal mode:
if {[regexp -nocase ***=$var1 $data]} {
# The substring was there...
}
The ***= means “the rest of this pattern is a literal string to match” and we can pass -nocase as an option to allow us to not need to use string toupper.