Tcl glob Command

last modified April 3, 2025

The Tcl glob command is used to match file names against patterns. It returns a list of files that match specified patterns. This is useful for file operations and directory listings.

Basic Definition

The glob command expands wildcard patterns to match file names. It supports various pattern matching characters similar to Unix shell globbing.

Syntax: glob ?switches? ?--? ?pattern ...?. The command returns a list of files matching the pattern(s). Switches modify its behavior.

Basic File Matching

This example shows the simplest usage of glob to list all .tcl files in the current directory.

basic_glob.tcl

set tcl_files [glob *.tcl]
puts "Tcl files: $tcl_files"

The pattern *.tcl matches all files ending with .tcl. The result is stored in tcl_files and printed. This is case-sensitive.

Multiple Patterns

glob can accept multiple patterns separated by spaces.

multi_pattern.tcl

set files [glob *.tcl *.txt]
puts "Matching files: $files"

This matches both .tcl and .txt files. The result is a combined list of all files matching either pattern. Order in the result isn't guaranteed.

Hidden Files

By default, glob doesn't match hidden files (starting with dot). The -nocomplain switch prevents errors when no matches are found.

hidden_files.tcl

set hidden_files [glob -nocomplain .*]
puts "Hidden files: $hidden_files"

The .* pattern matches hidden files. -nocomplain returns an empty list if no matches exist instead of raising an error.

Directory Recursion

The -directory and -recursive switches enable searching in specific directories and subdirectories.

recursive_glob.tcl

set all_tcl [glob -directory /path/to/tcl -recursive *.tcl]
puts "All Tcl files: $all_tcl"

This finds all .tcl files in /path/to/tcl and its subdirectories. The -recursive switch enables deep directory traversal.

Type Filtering

The -type switch filters matches by file type (file, directory, etc).

type_filter.tcl

set directories [glob -type d *]
puts "Directories: $directories"

This lists only directories in the current folder. -type d matches directories, while -type f would match only files.

Case Insensitive Matching

The -nocase switch enables case-insensitive pattern matching.

nocase_glob.tcl

set image_files [glob -nocase *.JPG *.png]
puts "Image files: $image_files"

This matches .jpg/.JPG and .png files regardless of case. Useful when dealing with files from different operating systems.

Best Practices

Error Handling: Use -nocomplain when matches might not exist.
Quoting: Protect patterns with braces {} to prevent substitution.
Performance: Be cautious with recursive globs on large directories.
Platform: Remember glob patterns differ across platforms.
Sorting: Sort results if order matters in your application.

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

Author

My name is Jan Bodnar, and I am a passionate programmer with extensive programming experience. I have been writing programming articles since 2007. To date, I have authored over 1,400 articles and 8 e-books. I possess more than ten years of experience in teaching programming.

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