Search in file for number, increment and replace - tcl

Question

I have a VHDL file which has a line like this:
constant version_nr :integer := 47;
I want to increment the number in this line in the file. Is there a way to accomplish this with TCL?

Answer 1

This is principally a string operation. The tricky bit is finding the line to operate on and picking the number out of it. This can be occasionally awkward, but it is mainly a matter of choosing a suitable regular expression (as this is the kind of parsing task that they excel at). A raw RE to do the matching would be this:
^\s*constant\s+version_nr\s*:integer\s*:=\s*\d+\s*;\s*$
This is essentially converting all possible places for a whitespace sequence into \s* (except where whitespace is mandatory, which becomes \s+) and matching the number with \d+, i.e., a digit sequence. We then add in parentheses to capture the interesting substrings, which are the prefix, the number, and the suffix:
^(\s*constant\s+version_nr\s*:integer\s*:=\s*)(\d+)(\s*;\s*)$
Now we have enough to make the line transform (which we'll do as a procedure so we can give it a nice name):
proc lineTransform {line} {
set RE {^(\s*constant\s+version_nr\s*:integer\s*:=\s*)(\d+)(\s*;\s*)$}
if {[regexp $RE $line -> prefix number suffix]} {
# If we match, we increment the number...
incr number
# And reconcatenate it with the prefix and suffix to make the new line
set line $prefix$number$suffix
}
return $line
}
In Tcl 8.7 (which you won't be using yet) you can write this as this more succinct form:
proc lineTransform {line} {
# Yes, this version can be a single (long) line if you want
set RE {^(\s*constant\s+version_nr\s*:integer\s*:=\s*)(\d+)(\s*;\s*)$}
regsub -command $RE $line {apply {{- prefix number suffix} {
# Apply the increment when the RE matches and build the resulting line
string cat $prefix [incr number] $suffix
}}}
}
Now that we have a line transform, we've just got to apply that to all the lines of the file. This is easily done with a file that fits in memory (up to a few hundred MB) but requires additional measures for larger files as you need to stream from one file to another:
proc transformSmallFile {filename} {
# Read data into memory first
set f [open $filename]
set data [read $f]
close $f
# Then write it back out, applying the transform as we go
set f [open $filename w]
foreach line [split $data "\n"] {
puts $f [transformLine $line]
}
close $f
}
proc transformLargeFile {filename} {
set fin [open $filename]
# The [file tempfile] command makes working with temporary files easier
set fout [file tempfile tmp [file normalize $filename]]
# A streaming transform; requires that input and output files be different
while {[gets $fin line] >= 0} {
puts $fout [transformLine $line]
}
# Close both channels; flushes everything to disk too
close $fin
close $fout
# Rename our temporary over the original input file, replacing it
file rename $tmp $filename
}