The primitive data-type of Tcl is strings and often we can find quotes on Tcl as strings only language. These Tcl strings can contain alphanumeric character, just numbers, Boolean, or even binary data. Tcl uses 16 bit unicode characters and alphanumeric characters can contain letters including non-Latin characters, number or punctuation.
Boolean value can be represented as 1, yes or true for true and 0, no, or false for false.
String Representations
Unlike other languages, in Tcl, you need not include double quotes when it’s only a single word. An example can be −
#!/usr/bin/tclsh set myVariable hello puts $myVariable
When the above code is executed, it produces the following result −
hello
When we want to represent multiple strings, we can use either double quotes or curly braces. It is shown below −
#!/usr/bin/tclsh
set myVariable "hello world"
puts $myVariable
set myVariable {hello world}
puts $myVariable
When the above code is executed, it produces the following result −
hello world hello world
String Escape Sequence
A character literal can be a plain character (e.g., ‘x’), an escape sequence (e.g., ‘\t’), or a universal character (e.g., ‘\u02C0’).
There are certain characters in Tcl when they are preceded by a backslash they will have special meaning and they are used to represent like newline (\n) or tab (\t). Here, you have a list of some of such escape sequence codes −
| Escape sequence | Meaning |
|---|---|
| \\ | \ character |
| \’ | ‘ character |
| \” | ” character |
| \? | ? character |
| \a | Alert or bell |
| \b | Backspace |
| \f | Form feed |
| \n | Newline |
| \r | Carriage return |
| \t | Horizontal tab |
| \v | Vertical tab |
Following is the example to show a few escape sequence characters −
#!/usr/bin/tclsh puts "Hello\tWorld\n\nAdglob";
When the above code is compiled and executed, it produces the following result −
Hello World Adglob
String Command
The list of subcommands for string command is listed in the following table −
| Sr.No. | Methods & Description |
|---|---|
| 1 | compare string1 string2Compares string1 and string2 lexographically. Returns 0 if equal, -1 if string1 comes before string2, else 1. |
| 2 | first string1 string2Returns the index first occurrence of string1 in string2. If not found, returns -1. |
| 3 | index string indexReturns the character at index. |
| 4 | last string1 string2Returns the index last occurrence of string1 in string2. If not found, returns -1. |
| 5 | length stringReturns the length of string. |
| 6 | match pattern stringReturns 1 if the string matches the pattern. |
| 7 | range string index1 index2Return the range of characters in string from index1 to index2. |
| 8 | tolower stringReturns the lowercase string. |
| 9 | toupper stringReturns the uppercase string. |
| 10 | trim string ?trimcharacters?Removes trimcharacters in both ends of string. The default trimcharacters is whitespace. |
| 11 | trimleft string ?trimcharacters?Removes trimcharacters in left beginning of string. The default trimcharacters is whitespace. |
| 12 | trimright string ?trimcharacters?Removes trimcharacters in left end of string. The default trimcharacters is whitespace. |
| 13 | wordend findstring indexReturn the index in findstring of the character after the word containing the character at index. |
| 14 | wordstart findstring indexReturn the index in findstring of the first character in the word containing the character at index. |
Examples of some commonly used Tcl string sub commands are given below.
String Comparison
#!/usr/bin/tclsh
set s1 "Hello"
set s2 "World"
set s3 "World"
puts [string compare $s1 $s2]
if {[string compare $s2 $s3] == 0} {
puts "String \'s1\' and \'s2\' are same.";
}
if {[string compare $s1 $s2] == -1} {
puts "String \'s1\' comes before \'s2\'.";
}
if {[string compare $s2 $s1] == 1} {
puts "String \'s2\' comes after \'s1\'.";
}
When the above code is compiled and executed, it produces the following result −
-1 String 's1' and 's2' are same. String 's1' comes before 's2'. String 's2' comes after 's1'.
Index of String
#!/usr/bin/tclsh set s1 "Hello World" set s2 "o" puts "First occurrence of $s2 in s1" puts [string first $s2 $s1] puts "Character at index 0 in s1" puts [string index $s1 0] puts "Last occurrence of $s2 in s1" puts [string last $s2 $s1] puts "Word end index in s1" puts [string wordend $s1 20] puts "Word start index in s1" puts [string wordstart $s1 20]
First occurrence of o in s1 4 Character at index 0 in s1 H Last occurrence of o in s1 7 Word end index in s1 11 Word start index in s1 6
When the above code is compiled and executed, it produces the following result −
Length of String
#!/usr/bin/tclsh set s1 "Hello World" puts "Length of string s1" puts [string length $s1]
When the above code is compiled and executed, it produces the following result −
Length of string s1 11
Handling Cases
#!/usr/bin/tclsh set s1 "Hello World" puts "Uppercase string of s1" puts [string toupper $s1] puts "Lowercase string of s1" puts [string tolower $s1]
When the above code is compiled and executed, it produces the following result −
Uppercase string of s1 HELLO WORLD Lowercase string of s1 hello world
Trimming Characters
#!/usr/bin/tclsh set s1 "Hello World" set s2 "World" puts "Trim right $s2 in $s1" puts [string trimright $s1 $s2] set s2 "Hello" puts "Trim left $s2 in $s1" puts [string trimleft $s1 $s2] set s1 " Hello World " set s2 " " puts "Trim characters s1 on both sides of s2" puts [string trim $s1 $s2]
When the above code is compiled and executed, it produces the following result −
Trim right World in Hello World Hello Trim left Hello in Hello World World Trim characters s1 on both sides of s2 Hello World
Matching Strings
#!/usr/bin/tclsh
set s1 "test@test.com"
set s2 "*@*.com"
puts "Matching pattern s2 in s1"
puts [string match "*@*.com" $s1 ]
puts "Matching pattern tcl in s1"
puts [string match {tcl} $s1]
When the above code is compiled and executed, it produces the following result −
Matching pattern s2 in s1 1 Matching pattern tcl in s1 0
Append Command
#!/usr/bin/tclsh set s1 "Hello" append s1 " World" puts $s1
When the above code is compiled and executed, it produces the following result −
Hello World
Format command
The following table shows the list of format specifiers available in Tcl −
| Specifier | Use |
|---|---|
| %s | String representation |
| %d | Integer representation |
| %f | Floating point representation |
| %e | Floating point representation with mantissa-exponent form |
| %x | Hexa decimal representation |
Some simple examples are given below −
#!/usr/bin/tclsh puts [format "%f" 43.5] puts [format "%e" 43.5] puts [format "%d %s" 4 tuts] puts [format "%s" "Tcl Language"] puts [format "%x" 40]
When the above code is compiled and executed, it produces the following result −
43.500000 4.350000e+01 4 tuts Tcl Language 28
Scan command
Scan command is used for parsing a string based to the format specifier. Some examples are shown below.
#!/usr/bin/tclsh
puts [scan "90" {%[0-9]} m]
puts [scan "abc" {%[a-z]} m]
puts [scan "abc" {%[A-Z]} m]
puts [scan "ABC" {%[A-Z]} m]
When the above code is compiled and executed, it produces the following result −
1 1 0 1
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