File Name Expansion and Management in Bash

Introduction to File Name Expansion and Management

Welcome! In this lesson, we will focus on file name expansion and management in Bash . File name expansion allows you to match file names using patterns. For example, you might want to find all .txt files in a directory or list all files that start with the word data . This lesson serves as a foundational block for managing files, significantly easing the manipulation and organization of files in more complex scripts. Let's get started!

Wildcards and Basic Expansion

File name expansion, also known as globbing, is a feature in shell environments like Bash that allows you to match filenames using patterns with special characters called wildcards. These wildcards are symbols like *, ?, and [] . These wildcards allow you to easily select files that fit certain criteria without typing each filename explicitly. This simplifies file management tasks such as listing, copying, or moving multiple files at once.

Matching Any Number of Characters: `*`

The * wildcard matches any number of characters (including none). This is useful when you need to list or act on files with similar names but different suffixes or prefixes. For example, ls *.txt lists all files ending with .txt . The * wildcard before .txt can represent any sequence of characters (including none), so any file name of any length that ends in .txt will be listed. Let's take a look: Shell #!/bin/bash # Create example files touch file1.txt draft.txt file2.sh ls *.txt #!/bin/bash # Create example files touch file1.txt draft.txt file2.sh ls *.txt Output text draft.txt file1.txt draft.txt file1.txt Only the files that end with .txt are included. file2.sh is not included because it does not match the specified pattern. Now let's use * to search for any files that begin with file . ls file* matches any name that begins with file followed by any sequence of characters. Shell #!/bin/bash # Create example files touch file1.txt draft.txt file2.sh ls file* #!/bin/bash # Create example files touch file1.txt draft.txt file2.sh ls file* Output: text file1.txt file2.sh file1.txt file2.sh Only the files that start with file are included. draft.txt does not match the pattern, so it is not included.

Matching Exact Character Counts: `?`

The ? wildcard matches exactly one character. This is useful for filtering files that have specific character lengths. For example, ls draft?.md matches any file that starts with draft and has one character before .md Shell #!/bin/bash # Create example files touch draft1.md draftA.md draft1A.md ls draft?.md #!/bin/bash # Create example files touch draft1.md draftA.md draft1A.md ls draft?.md Output: text draft1.md draftA.md draft1.md draftA.md draft1A.md is not included in the output because it has two characters between draft and .md . You can match multiple characters by using any number of ? wildcards. Let's examine ls draft??.md . Two ? wildcards represent exactly two characters, so any file name that starts with draft and has two characters before .md will be listed. Shell #!/bin/bash # Create example files touch draft1.md draftA.md draft1A.md ls draft??.md #!/bin/bash # Create example files touch draft1.md draftA.md draft1A.md ls draft??.md Output: text draft1A.md draft1A.md draft1.md and draftA.md are not included because they only have a single character between draft and .md

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Matching Ranges: `[]`

The [] wildcard allows you to match a specific set or range of characters. You can specify ranges of characters by using a hyphen (-) between two characters. A range represents all characters between the two specified characters, inclusive.

Let's look at ls file[1-3].txt. The [1-3] wildcard will match any one character from 1 to 3.

Shell

#!/bin/bash

# Create example files
touch file.txt file1.txt file2.txt file4.txt

ls file[1-3].txt

#!/bin/bash

# Create example files
touch file.txt file1.txt file2.txt file4.txt

ls file[1-3].txt

Output:

text

file1.txt
file2.txt

file1.txt
file2.txt

The command does not match file.txt because there is no digit between file and .txt. file4.txt is not matched because 4 does not fall in the [1-3] range.

To include multiple ranges in the [] wildcard, you simply list them side by side within the brackets. file[1-35-6].txt will match any name that starts with file followed by the numbers 1, 2, 3, 5, 6, then ends with .txt

Let's take a look:

Shell

#!/bin/bash

# Create example files
touch file1.txt file2.txt file3.txt file4.txt file5.txt file6.txt file7.txt

ls file[1-35-6].txt

#!/bin/bash

# Create example files
touch file1.txt file2.txt file3.txt file4.txt file5.txt file6.txt file7.txt

ls file[1-35-6].txt

Output

text

file1.txt
file2.txt
file3.txt
file5.txt
file6.txt

file1.txt
file2.txt
file3.txt
file5.txt
file6.txt

file4.txt and file7.txt are not included because they fall outside of the ranges 1-3 and 5-6.

Similarly, you can use letters in ranges as well.

Shell

#!/bin/bash

# Create example files
touch fileA.txt fileB.txt fileC.txt fileD.txt 

ls file[A-C].txt

#!/bin/bash

# Create example files
touch fileA.txt fileB.txt fileC.txt fileD.txt 

ls file[A-C].txt

Output:

text

fileA.txt
fileB.txt
fileC.txt

fileA.txt
fileB.txt
fileC.txt

The [A-C] range matches A, B, and C, so fileA.txt, fileB.txt, and fileC.txt are listed. fileD.txt is not listed because D is outside the [A-C] range.

If you want to include a range that is only a single character, you use just that character without a hyphen.

Shell

#!/bin/bash

# Create example files
touch file1.txt file2.txt file4.txt
touch fileA.txt fileB.txt fileC.txt

ls file[1-3B].txt

#!/bin/bash

# Create example files
touch file1.txt file2.txt file4.txt
touch fileA.txt fileB.txt fileC.txt

ls file[1-3B].txt

Output:

text

file1.txt
file2.txt
fileB.txt

file1.txt
file2.txt
fileB.txt

This pattern matches any name that start with file, followed by a 1, 2, 3, or B, then ends with .txt.

Introduction to File Name Expansion and Management

Wildcards and Basic Expansion

Matching Any Number of Characters: `*`

Matching Exact Character Counts: `?`

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Matching Ranges: `[]`

Matching Lists: {}

Combining Wildcards for Flexible Matching

Case Sensitivity

Summary and Next Steps