Tcl Script Cheatsheet
Basic Language Syntax
Print to the screen
puts "Hello, world!"
Variables
Variables are strings
# Set x to string hello
set x hello
# Set my_variable to string 22
set my_variable 22
# Expand a variable
puts "The value of my_variable is $my_variable"
> The value of my_variable is 22
White space is used to delimit items in a list
set y "One two three"
# Print a list with one item per line
join $y \n
> One
> Two
> Three
If you want a variable to be a string including whitespace and not a list, use { }
set z {One two three}
join $z \n
> One two three
Get the length of a list
set a "One two three"
llength $a
> 3
Arrays are zero indexed
set a "One two three"
lindex $a 1
> two
Maths
The expr function performs mathematical operations on string variables that are numbers.
set a 10
set b 20
expr $a * $b
expr ($a * $b) + 10
> 200
> 210
Integer maths is used unless one variable is a float
set a 10
set b 3
set c 3.0
expr $a / $b
expr $a / $c
> 3
> 3.3333333333333335
Command expansion
Square brackets allow inline command expansion
set x 10
set y 2
set z 3.0
puts "10 / 2 is [expr $x / $y]"
puts "(10 / 2) / 3.0 is [expr [expr $x / $y] / $z]"
> 10 / 2 is 5
> (10 / 2) / 3.0 is 1.6666666666666667
Loops
Step through each item in a list
set values "1 2 3"
foreach value $values {puts "Value: $value"}
> Value: 1
> Value: 2
> Value: 3
Curly braces can be split over multiple lines
foreach value $values {
puts "Value: $value"
}
While loops can also be used
set x 0
while {x < 3} {
puts "[incr x]"
}
> 1
> 2
> 3
If statements
If, elseif, and else are all allowed
set x 3
if {$x > 5} {
puts "X is > 5"
} else {
puts "X is <= 5"
}
> X is <= 5
set y 2
if {$y == 1} {
puts "Y is 1"
} elseif {$y == 2} {
puts "Y is 2"
} else {
puts "Y is not 1 or 2"
}
> Y is 2
File handling
Open a file for writing using open file_name.ext w. This returns a file handle.
Write to a file using puts followed by the file handle and the string to write.
set fh [open test.txt w]
puts $fh "Hello, World"
puts $fh "Hi!"
close $fh
Open a file for reading using open file_name.ext r.
Use gets to read a line from the file. If gets is called with a single argument (the file handle), it returns a line from the file as a string.
set fh [open test.txt r]
puts [gets $fh]
close $fh
If gets is called with two arguments, it returns the line length, or -1 when at end of the file. The line's contents is stored in the second variable.
set fh [open test.txt r]
puts "Line length: [gets $fh line]"
puts "Line contents $line"
close $fh
You can loop through a whole file like this:
set fh [open test.txt r]
set line_number 0
while {[gets $fh line] >= 0} {
puts "[incr line_number]: $line"
}
close $fh
Procedures
You can make procedures like this
proc print_file filename {
set fh [open $filename r]
puts [read $fh]
close $fh
}
print_file test.txt
Or with multiple arguments
proc say_hi {name1 name2} {
puts "Hi $name1"
puts "Hi $name2"
}
say_hi Bob Steve
> Hi Bob
> Hi Steve
Time
Get a unix timestamp using clock seconds. You can format it as a nice date / time using clock format.
clock seconds
clock format [clock seconds] -format "%Y-%m-%d %H:%M:%S"
1665861034
2022-10-15 20:10:34
Get the last modified time of a file:
file mtime file_name.ext
clock format [clock seconds] -format "%Y-%m-%d %H:%M:%S"
1665861034
2022-10-15 20:10:34