How to Extract Filename and Extension in Bash
Working with file paths is a common task in Bash scripting, whether you're processing files, creating backups, or organizing data. Extracting components like filenames, extensions, and directory paths from full file paths is essential for many automation tasks.
This guide covers multiple methods to extract filename and extension information from file paths, using both built-in Bash features and external commands.
Using Parameter Expansion (Recommended)
Bash parameter expansion provides the most efficient way to extract filename components without external commands:
filepath="/home/user/documents/report.pdf"
# Extract filename with extension
filename="${filepath##*/}"
echo "Filename: $filename" # Output: report.pdf
# Extract filename without extension
name="${filename%.*}"
echo "Name: $name" # Output: report
# Extract extension
extension="${filename##*.}"
echo "Extension: $extension" # Output: pdf
# Extract directory path
directory="${filepath%/*}"
echo "Directory: $directory" # Output: /home/user/documents
Here's how these patterns work:
${filepath##*/}- removes everything up to and including the last/${filename%.*}- removes the shortest match of.and everything after from the end${filename##*.}- removes everything up to and including the last.${filepath%/*}- removes the shortest match of/and everything after from the end
Creating Reusable Functions
Here's a comprehensive function that extracts all components:
parse_filepath() {
local filepath="$1"
local -n result="$2" # Name reference for associative array
# Initialize result array
result["full_path"]="$filepath"
result["filename"]="${filepath##*/}"
result["directory"]="${filepath%/*}"
result["name"]="${result["filename"]%.*}"
result["extension"]="${result["filename"]##*.}"
# Handle edge cases
if [[ "${result["filename"]}" == "${result["extension"]}" ]]; then
result["extension"]="" # No extension found
fi
if [[ "${result["directory"]}" == "$filepath" ]]; then
result["directory"]="." # No directory in path
fi
}
# Usage
declare -A file_info
parse_filepath "/var/log/system.log" file_info
echo "Full path: ${file_info[full_path]}"
echo "Directory: ${file_info[directory]}"
echo "Filename: ${file_info[filename]}"
echo "Name: ${file_info[name]}"
echo "Extension: ${file_info[extension]}"
Using basename and dirname Commands
The basename and dirname commands provide an alternative approach:
filepath="/home/user/documents/report.pdf"
# Extract filename
filename=$(basename "$filepath")
echo "Filename: $filename" # Output: report.pdf
# Extract filename without extension
name=$(basename "$filepath" .pdf)
echo "Name: $name" # Output: report
# Extract directory
directory=$(dirname "$filepath")
echo "Directory: $directory" # Output: /home/user/documents
For extension extraction with basename:
# Generic extension extraction with basename
filename=$(basename "$filepath")
extension="${filename##*.}"
name=$(basename "$filepath" ".$extension")
echo "Name: $name"
echo "Extension: $extension"
Handling Multiple Extensions
For files with multiple extensions like archive.tar.gz:
extract_extensions() {
local filepath="$1"
local filename="${filepath##*/}"
local name extension full_extension
# Get the first part (before any dots)
name="${filename%%.*}"
# Get everything after the first dot
full_extension="${filename#*.}"
# Get just the last extension
extension="${filename##*.}"
echo "Original: $filepath"
echo "Name: $name"
echo "Last extension: $extension"
echo "Full extension: $full_extension"
}
# Examples
extract_extensions "archive.tar.gz"
# Name: archive
# Last extension: gz
# Full extension: tar.gz
extract_extensions "backup.sql.bz2"
# Name: backup
# Last extension: bz2
# Full extension: sql.bz2
Processing Multiple Files
Here's how to process multiple files and extract their components:
process_files() {
local files=("$@")
printf "%-20s %-15s %-10s %-30s\n" "NAME" "EXTENSION" "SIZE" "DIRECTORY"
printf "%s\n" "$(printf '=%.0s' {1..75})"
for filepath in "${files[@]}"; do
if [[ -f "$filepath" ]]; then
local filename="${filepath##*/}"
local name="${filename%.*}"
local extension="${filename##*.}"
local directory="${filepath%/*}"
local size=$(stat -c%s "$filepath" 2>/dev/null || echo "N/A")
# Handle files without extensions
if [[ "$filename" == "$extension" ]]; then
extension="(none)"
fi
printf "%-20s %-15s %-10s %-30s\n" \
"${name:0:19}" "${extension:0:14}" "$size" "${directory:0:29}"
fi
done
}
# Usage
process_files /home/user/*.txt /var/log/*.log
Batch File Renaming
A practical example using filename extraction for batch renaming:
batch_rename() {
local pattern="$1"
local replacement="$2"
local directory="${3:-.}"
for filepath in "$directory"/*; do
if [[ -f "$filepath" ]]; then
local filename="${filepath##*/}"
local name="${filename%.*}"
local extension="${filename##*.}"
local new_name="${name//$pattern/$replacement}"
# Handle files without extensions
if [[ "$filename" == "$extension" ]]; then
local new_filename="$new_name"
else
local new_filename="$new_name.$extension"
fi
if [[ "$filename" != "$new_filename" ]]; then
echo "Renaming: $filename -> $new_filename"
mv "$filepath" "${filepath%/*}/$new_filename"
fi
fi
done
}
# Usage: replace "old" with "new" in all filenames
batch_rename "old" "new" "/path/to/files"
Creating Backup Files
Extract components to create backup files with timestamps:
create_backup() {
local original_file="$1"
local timestamp=$(date +"%Y%m%d_%H%M%S")
local filename="${original_file##*/}"
local name="${filename%.*}"
local extension="${filename##*.}"
local directory="${original_file%/*}"
# Handle files without extensions
if [[ "$filename" == "$extension" ]]; then
local backup_file="${directory}/${name}_${timestamp}"
else
local backup_file="${directory}/${name}_${timestamp}.${extension}"
fi
if cp "$original_file" "$backup_file"; then
echo "Backup created: $backup_file"
else
echo "Failed to create backup for: $original_file"
return 1
fi
}
# Usage
create_backup "/etc/nginx/nginx.conf"
# Output: Backup created: /etc/nginx/nginx_20240708_143022.conf
Working with URLs
The same techniques work for extracting components from URLs:
parse_url_path() {
local url="$1"
# Extract path from URL (everything after domain)
local path="${url#*://*/}"
path="/$path"
# Extract filename from path
local filename="${path##*/}"
local name="${filename%.*}"
local extension="${filename##*.}"
local directory="${path%/*}"
echo "URL: $url"
echo "Path: $path"
echo "Directory: $directory"
echo "Filename: $filename"
echo "Name: $name"
echo "Extension: $extension"
}
# Usage
parse_url_path "https://example.com/downloads/files/document.pdf"
Advanced Pattern Matching
For more complex filename patterns:
extract_version_info() {
local filename="$1"
# Extract base name without version and extension
# Handles patterns like: app-1.2.3.tar.gz, tool_v2.1.exe
local base_name="${filename%%-*}" # Remove from first dash
base_name="${base_name%%_*}" # Remove from first underscore
# Extract version pattern (digits and dots)
local version=""
if [[ "$filename" =~ ([0-9]+\.[0-9]+(\.[0-9]+)?(-[a-zA-Z0-9]+)?) ]]; then
version="${BASH_REMATCH[1]}"
fi
echo "Base name: $base_name"
echo "Version: $version"
}
# Examples
extract_version_info "nginx-1.18.0.tar.gz"
# Base name: nginx
# Version: 1.18.0
extract_version_info "app_v2.1-beta.zip"
# Base name: app
# Version: 2.1-beta
Best Practices
- Use parameter expansion for better performance and fewer external dependencies
- Handle edge cases like files without extensions or complex paths
- Test with various path formats including relative paths and URLs
- Validate inputs before processing to avoid unexpected behavior
- Use quotes around variables to handle paths with spaces
- Consider special files like hidden files starting with dots
Extracting filename and extension information is fundamental to file processing in Bash. These techniques provide robust methods for parsing file paths, whether you're building file processors, backup systems, or general automation scripts.
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