Now that we can open, read, write, and close a file, it is time to put this knowledge to work in a real world manner. We will now create a Tcl script that accesses a file, reorders the stored data, and then outputs it to a secondary file. This is similar to a file handling procedure used to clean up user supplied files.
Using the text editor of your choice create a text file containing the following text:
1,3,5,7,8,2,4,6,9
Save the file in your working directory as input.txt.
Using the text editor of your choice create the following Tcl script and save it in your working directory as filehandler.tcl.
# Check that a filename was provided
if { $argc>0 & $argv>0} {
# Assign the filename to a variable
set fname [lindex $argv 0]
# Open the file for read-only access
set fp [open $fname r]
# Read the contents of the file into a variable
set data [read $fp]
#Close the input file
close $fp
# Split the data and create a Tcl list
set input [split $data ","]
# Sort the list and load it into another list
set output [lsort -increasing $input]
# Open a file to write the data to
set fp [open output.txt w]
# Read through the list and write the data
foreach item $output {
puts $fp $item
}
#Close the file
close $fp
} else {
puts "No filename provided... Exiting Script"
exit
}
Launch your Tcl shell appropriately, based on your operating platform. Enter the following command line:
% tclsh filehandler.tcl input.txt
%
By combining the capabilities of the Tcl, file handling commands with the Tcl list functionality we are able to read in a comma delimited list of data and output it to a file sorted and line-by-line. To confirm the output, use the text editor of your choice and view the file output.txt. It should contain a sorted listing of the integers provided, one per line, as shown next:
1
2
3
4
5
6
7
8
9