Escape

When working in the shell, special characters like ?, *, and [ ] are interpreted by the globbing engine for filename matching. Preceding these characters with a backslash (\) or quoting them forces the shell to treat them as literal characters.

1. Creating Sample Files

First, generate files whose names differ only by the first letter:

$ touch sail hail mail fail tail
$ ls
fail hail mail sail tail

2. Wildcard vs. Literal ?

2.1 Using the ? Wildcard

The ? matches exactly one character. Attempting to create ?ail without escaping:

$ touch ?ail
$ ls
fail hail mail sail tail

No new file appears because ?ail expanded to all existing matches (fail, hail, etc.).

2.2 Escaping ? for Literal Filenames

To create a file literally named ?ail:

$ touch \?ail
$ ls
?ail fail hail mail sail tail

3. Listing Files with a Leading ?

You can retrieve the ?ail file by escaping or quoting the pattern:

$ ls \?ail
?ail

$ ls "?ail"
?ail

Both methods disable globbing and match the literal filename.

4. Mixing Literals and Wildcards

Assume these files exist:

$ touch hail fail mail \?ail
$ touch hailTwo failTwo mailTwo \?ailTwo
$ ls
?ail ?ailTwo fail failTwo hail hailTwo mail mailTwo

To list all files starting with a literal ?ail:

$ ls \?ail*
?ail  ?ailTwo

Here, \?ail* treats \? as literal ? and * as the wildcard for any suffix.

5. Merging Globs into a Single Pattern

For files named Pail, Pail*, and PailTwo:

$ touch Pail Pail* PailTwo
$ ls
Pail Pail* PailTwo

You can match them all using:

$ ls Pail*
Pail Pail* PailTwo

The * wildcard expands to zero or more characters following Pail.

6. Quick Reference Table

Summary

• A backslash (\) or quotes disables globbing for the next character or entire string.
• Use wildcards (?, *, [ ]) without escaping to match patterns.
• Combine escaped literals and wildcards for precise filename operations.

Links and References

• GNU Bash Manual – Pattern Matching
• Bash Guide: Filename Expansion