how to read every section of a file using tcl? - tcl

Question

I have just started learning tcl and I have a problem with reading a big file.
I have a data file which looks like the following:
420
360 360 360 3434.01913
P 6.9022 0.781399 -0.86106
C 4.36397 -0.627479 3.83363
P 6.90481 5.42772 3.08491
....
and ends like this:
P -7.21325 1.71285 -0.127325
C -4.14243 0.41123 4.67585
420
360 360 360 3210.69667
so C is the last line of one section and 420 is the start of the next section.so every 420 lines make a section of the whole file.
how can I read every section of this file and have it as like say "frame1" and do this until the end of the file (having frame2, frame3 and ...).
I have come up with a simple script just to read the whole file line by line but I do not know how to do this.Thanks

Answer 1

The answer to your question "how to read every section of a file using tcl?" is quite simply "keep reading until you run out of lines".
The answer to the question "how to count sections and skip header lines" is something like this:
while { ...condition... } {
if {[gets $fp line] < 0} break
lassign $line name x y z
if {$name eq "420"} {
incr section_counter
} elseif {$name in {P C}} {
# do something with the data
}
}
The condition for your while loop will be tested once for each line read. The first if command breaks out of the loop once the entire file has been read. You don't need to split the line you read unless you expect one of the lines to contain a string that isn't a proper list. Once you have assigned the fields of the line into the variables, you can look inside name to see what kind of line you got. The second if command says that if $name is the string "420", the section counter is increased. If, on the other hand, $name contains "P" or "C", you have a data line to process. If neither of these conditions are fulfilled, you have the line after a "420" line, which is simply ignored.
Documentation: break, gets, if, incr, lassign, while