Mastering Tcl: A Beginner's Guide to Tool Command Language part 4

File Operation Examples in Tcl

Let's explore file operations in Tcl by creating a chipworld.txt file and placing it in the bin directory.

The input file 

The Input File

Reading the Entire File at Once

Example (1):

Example 1:

 set fp [open "chipworld.txt" r]
set content [read $fp]
puts $content
close $fp
    

Output:

chip world is the best vlsi blog

Reading File Line by Line

Example (1): read the following file 

The input file 

tcl

set file [open "chipworld.txt" r]
while {[gets $file data] >= 0} {
    puts $data
}
close $file

Output:

chip world is the best vlsi blog
learn TCL with us

Writing File Contents

Example (1): Note that this code will remove all file content and write the required content.

 set file [open "chipworld.txt" w]
puts $file "TCL (Tool Command Language)"
close $files

    

The output file 

The output file 

Nested List and File Operation

We consider a file with multiple lines as a nested list.

Example (1): We want to write multiple lines to a file.

 set file [open "chipworld.txt" w]
puts $file "chip world is the best vlsi blog"
puts $file "learn TCL with us"
puts $file "please, follow us"
puts $file "please, visit us"
close $file

    

the output file 

To read the last elements of each line:

tcl

set file [open "chipworld.txt" r]
while {[gets $file line] >= 0} {
    puts "[lindex $line end]"
}
close $file

Output:

blog
us
us
us

Arrays in Tcl

Array Syntax

tcl

set zoo(animal1) donkey
set zoo(animal2) caw
set zoo(animal3) lion
puts $zoo(animal1) ;# Output: donkey
puts $zoo(animal2) ;# Output: caw
puts $zoo(animal3) ;# Output: lion

Array Commands

Array Size:

tcl

array size zoo ;# Output: 3

Array Names:

 array names zoo ;# Output: animal2 animal3 animal1 
    

Array Stack:

 array get zoo ;# Output: animal2 caw animal3 lion animal1 donkey 
    

Using Arrays in Foreach Loop

Example 1:

 foreach name_array [array names zoo] {
    puts "$name_array $zoo($name_array)"
}

    

Output:

animal2 caw
animal3 lion
animal1 donkey

Example 2:

 foreach {zoo_array zoo_name} [array get zoo] {
    puts "$zoo_array $zoo_name"
}

    

Output:

animal2 caw
animal3 lion
animal1 donkey

Test for Understanding

Question 1: Write to a file line by line and get the last element of the file.

Solution:

Write to chipworld.txt file:

 set file [open "chipworld.txt" w]
puts $file "chip world is the best vlsi blog"
puts $file "learn TCL with us"
puts $file "please, follow us"
puts $file "please, visit us"
close $file

    

the output file 

Reading the last word in the file:

 set file [open "chipworld.txt" r]
set last_element {}
while {[gets $file line] >= 0} {
    set last_element [lindex $line end]
}
puts "Last element of the file: $last_element"
close $file

    

Output:

us