Tcl Tutorial Lesson 18

String comparisons - compare match first last wordend

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There are 6 string subcommands that do pattern and string matching. These are relatively fast operations, certainly faster than regular expressions, albeit less powerful.

string compare string1 string2: Compares string1 to string2 and returns a number -1, 0 or 1 based on the comparison. These comparisons are done alphabetically, not numerically - in other words "a" is less than "b", and "10" is less than "2".

-1 if string1 is less than string2
0 if string1 is equal to string2
1 if string1 is greater than string2

string first string1 string2: Returns the index of the character in string1 that starts the first match to string2, or -1 if there is no match.

string last string1 string2: Returns the index of the character in string1 that starts the last match to string2, or -1 if there is no match.

string wordend str i: Returns the index of the character just after the last one in the word which contains the i'th character of str. A word is any contiguous set of letters, numbers or underscore characters, or a single other character.

string wordstart str i: Returns the index of the first character in the word that contains the i'th character of str. A word is any contiguous set of letters, numbers or underscore characters, or a single other character.

string match pattern str: Returns 1 if the pattern matches the entire string. The pattern is a glob style pattern.

Example

set fullpath "/usr/home/tcl/TclTutor/Lsn.17"
set relativepath "CVS/Entries"
set directorypath "/usr/bin/"

set paths [list $fullpath $relativepath $directorypath]

foreach path $paths  {
    set first [string first "/" $path]
    set last [string last "/" $path]

    # Report whether path is absolute or relative

    if {$first != 0} {
        puts "$path is a relative path"
    } else {
        puts "$path is an absolute path"
    }

    # If "/" is not the last character in $path, report the
    # last word. Else, remove the last "/", and find the next
    # to last "/", and report the last word.

    incr last
    if {$last != [string length $path]} {
        set name [string range $path $last end]
        puts "The file referenced in $path is $name"
    } else {
        incr last -2;
        set tmp [string range $path 0 $last]
        set last [string last "/" $tmp]
        incr last;
        set name [string range $tmp $last end]
        puts "The final directory in $path is $name"
    }

    # CVS is a directory created by the CVS source code
    # control system.

    if {[string match "*CVS*" $path]} {
        puts "$path is part of the source code control tree"
    }

    # Compare to "a" to determine whether the first char is
    # upper or lower case
    set comparison [string  compare $name "a"]
    if {$comparison >= 0} {
        puts "$name starts with a lowercase letter\n"
    } else {
        puts "$name starts with an uppercase letter\n"
    }
}

Resulting output

Note: the analysis of the various parts in the path name is just an illustration of string commands. In practice you should use the file command.

/usr/home/tcl/TclTutor/Lsn.17 is an absolute path
The file referenced in /usr/home/tcl/TclTutor/Lsn.17 is Lsn.17
Lsn.17 starts with an uppercase letter

CVS/Entries is a relative path
The file referenced in CVS/Entries is Entries
CVS/Entries is part of the source code control tree
Entries starts with an uppercase letter

/usr/bin/ is an absolute path
The final directory in /usr/bin/ is bin
bin starts with a lowercase letter

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