Tcl split Command

last modified April 3, 2025

The Tcl split command divides strings into lists using specified delimiters. It's essential for parsing and processing textual data in Tcl.

Basic Definition

The split command breaks a string into list elements based on delimiter characters. If no delimiter is specified, it splits on whitespace.

Syntax: split string ?splitChars?. The optional splitChars parameter defines the delimiter(s). The command returns a Tcl list.

Splitting on Whitespace

This example demonstrates the default behavior of splitting on whitespace.

basic_split.tcl

set text "apple banana cherry"
set fruits [split $text]
puts $fruits

The string is split at each space character, creating a three-element list. The puts command outputs the resulting list: apple banana cherry.

Splitting on Specific Characters

Here we split a string using a comma as the delimiter.

split_comma.tcl

set csv "red,green,blue,yellow"
set colors [split $csv ","]
puts $colors

The comma-separated string is split into individual color names. Each comma becomes a list element separator. The output is a four-element list.

Splitting on Multiple Delimiters

The split command can use multiple delimiter characters simultaneously.

split_multiple.tcl

set data "apple:banana;cherry,date"
set items [split $data ":;,"]
puts $items

This splits the string at any colon, semicolon, or comma. The result is a four-element list containing the fruit names without the delimiters.

Splitting Lines from a File

A common use case is splitting file content into lines using newline characters.

split_lines.tcl

set file_content "First line\nSecond line\nThird line"
set lines [split $file_content "\n"]
foreach line $lines {
    puts "Line: $line"
}

The newline character (\n) serves as the delimiter, splitting the content into separate lines. The foreach loop then processes each line individually.

Splitting with Empty Elements

Consecutive delimiters create empty list elements, which can be useful.

split_empty.tcl

set data "one,,three,four,,six"
set items [split $data ","]
puts "Number of elements: [llength $items]"
puts $items

The double commas create empty elements in the resulting list. The llength command shows there are six elements, including the empty ones.

Splitting Path Components

File paths can be split into components using the directory separator.

split_path.tcl

set path "/usr/local/bin/tclsh"
set components [split $path "/"]
puts "Components:"
foreach comp $components {
    if {$comp ne ""} {
        puts $comp
    }
}

This splits a Unix path into its components. The empty first element (from the leading slash) is skipped in the output. Each directory level becomes a list item.

Best Practices

Trim Whitespace: Use string trim before splitting if needed.
Empty Elements: Be aware that consecutive delimiters create empty elements.
Performance: For large strings, consider alternative approaches.
Join Command: Remember join is the inverse operation.
Special Characters: Escape special characters properly in delimiters.

This tutorial covered the Tcl split command with practical examples showing its usage in different scenarios.

Author

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