In a while conditional I am read-assigning and then testing a variable as boolean expression.
Let’s say I am reading a file and want to discard lines that are comments. Yet the following does not enter the loop. The puts never prints.
while {[gets $fp line] >= 0 && [regexp {^#} $line] ==0} {
puts "Got valid data"
}
Seems the gets assignment of line and it’s evaluation can’t be in the same conditional. Is that corroborated in TCL spec?
For sure this one works but I would have liked to do the conditional in one statement.
while {[gets $fp line] >= 0 } {
if {[regexp {^#} $line] == 0 } {
puts "Got valid data"
}
}
Cheers.
1
as per @glennjackman, logic is flawed.
here’s a trivial example using a function to read/filter input
cat gert.tcl
#!/usr/bin/env tclsh
proc filteredRead {fstream lineVar prune} {
upvar $fstream handle;
upvar $lineVar line;
upvar $prune filter; #skip lines matching this regexp
while {[gets $fstream line] >= 0} {
if {[regexp $prune $line]} {
continue
}
return 1
}
return 0
}
if {$argc == 0} {
puts "Usage: $argv0 <filename> [filter (default is ^#)]"
exit 1
}
set filename [lindex $argv 0]
set filter {^#}; # default filter is comment lines
if {$argc == 2} {
set filter [lindex $argv 1]
}
if {![file readable $filename]} {
puts "Error: File '$filename' does not exist or is not readable."
exit 1
}
set handle [open $filename r]
set line ""
puts "nfiltering lines matching: [$filter]"
while {[filteredRead $handle line $filter]} {
puts "[$line]"
}
close $handle
#
#invoke against an simple test file
#
cat input
# i'm a comment, skip me
print me
# i'm also comment, skip me
and me
# skip me
# and me
i will be printed
# i'll be skipped
./gert.tcl input
filtering lines matching: [^#]
[print me ]
[]
[and me]
[]
[i will be printed]
hope this helps.
You can’t skip a while loop iteration from within the condition; there isn’t a handler in place for continue exceptions at that point. (Normally they get compiled to jumps.) Using an if inside the body of the while is idiomatic.