Protecting Special Characters In Filenames With Find -Exec
Escaping Special Characters in Filenames
Filenames containing special characters like spaces, asterisks, and parentheses can cause errors when used with commands in shells like Bash. The shell attempts to interpret these characters instead of treating them as literals which leads to unintended behavior. For example, an asterisk is used to wildcard match any characters in globbing. We need to properly escape these special characters when passing filenames to commands so they are treated as part of the filename itself.
Why Special Characters Cause Issues
The shell environment attempts to interpret special characters which causes filenames with those characters to not be handled properly. Some examples of issues that arise include:
- Spaces – The shell splits on spaces when tokenizing commands which separates the filename
- Asterisks – Used for globbing and wildcard matching which expands the filename
- Parentheses – Used for subshell execution which causes errors
Without escaping these special characters first, commands passed filenames containing them will not work as expected. The filename itself gets broken up or expanded incorrectly leading to “No such file or directory” errors or unintentionally destructive behavior on the wrong set of files.
Characters like spaces, asterisks, parentheses need escaping
To treat filenames with special characters literally, we need to escape the characters first. This indicates to the shell not to interpret them so they get passed to commands as part of the intended filename. Some examples of escaping special characters include:
- Spaces – Add backslashes (\) before spaces
- Asterisks – Precede with backslashes
- Parentheses – Precede with backslashes
With special characters properly escaped, commands will receive the full intended filename as an argument allowing correct behavior with files containing those characters.
Using find -exec to Escape Filenames
The find command offers a convenient way to process files matching certain criteria. We can use the -exec option to execute a command on each file found, escaping special characters in the filenames automatically.
exec option runs command on each file found
The -exec option for find specifies a command to execute on each file found by the search. The full path to the file can be substituted via the {} characters. For example:
find . -type f -exec cp {} /backup \;
This command finds all regular files in the current directory recursively, copying each one to the /backup location. The \; signifies the end of the -exec command.
Use \- to escape special characters
find automatically escapes special characters when substituting file paths via {} substitution. This means we don’t need to manually escape characters like spaces, asterisks or parentheses when using -exec.
For example, to copy a file named “my file (1).txt” to “my_file_(1).txt”, escaping parentheses:
find . -type f -name "my file (1).txt" -exec cp {} my_file_(1).txt \;
The parentheses are automatically escaped when the filename is substituted into the cp command.
Example: find . -type f -exec mv ‘{}’ ‘\{}.txt’ \;
Here is an example command to rename files by adding a .txt extension, which also demonstrates escaping the substituted filename itself:
find . -type f -exec mv '{}' '\{}.txt' \;
Breaking this down:
- find searches the current directory for all regular files
- -exec runs the mv command on each file found
- {} substitutes the file path/name into the mv command
- The filename {} is escaped with \’ to avoid issues with special characters
- The extension .txt is appended to the escaped filename \{}
- \; signifies the end of the -exec command
This shows how find can be used to safely operate on files with special characters by automatically handling the escaping for us.
Common Use Cases
Escaping special characters in filenames is useful in many scenarios involving scripting, bulk renaming files, and passing files to commands.
Renaming files with spaces
It’s common to need to rename files containing spaces without losing the spaces as word separators:
find . -depth -name "* *" -exec mv '{}' '\{}' \;
This renames files with spaces but maintains the spaces in the new filename by escaping the substituted name \{}.
Passing filenames to other commands
Any time we need to pass a filename to another command, escaping ensures special characters don’t cause issues:
find . -type f -exec tar cf archive.tar '{}' \;
This creates a tar archive of the found files. Escaping protects spaces, wildcard characters, etc. in the filenames.
Scripting bulk filename changes
find can be used in scripts to perform bulk filename changes across many files:
#!/bin/bash
find . -depth -name "* *" -exec mv '{}' '\{}_modified' \;
The portability of find across scripting languages and shells makes it an ideal choice for portable batch/bulk renaming operations.
Best Practices
Following best practices helps avoid issues when working with filenames containing special characters.
Always escape filenames passed to commands
Even if you believe a set of filenames is safe or scrubbed, it’s best to escape filenames whenever passing them as arguments to commands like mv, cp, tar, etc. find’s automatic escaping via {} handles this for us.
Use single quotes around filenames
When manually dealing with filenames in the shell, enclosing them in single quotes avoids interpretting special characters like spaces, asterisks, etc:
cp 'file name with spaces.txt' 'file_name_with_spaces.txt'
Test escapes before running destructive operations
It can be dangerous to attempt large filename changes across many files at once. Test find commands with echo first before using destructive operations:
find . -depth -name "* *" -exec echo mv '{}' '\{}_modified' \;
This shows what would happen before pulling the trigger to minimize mistakes.
Additional Tools
Some other useful tools that help work with special characters in filenames include:
basename – strips directory from filename
The basename command returns the filename without any leading directory information, useful for stripping paths:
basename 'path/to/my file.txt'
Returns: ‘my file.txt’
printf – uses escapes like \n and \t
An alternative to echo, printf also expands escape sequences like newlines and tabs:
printf 'My file\nis called...\n\t%s' 'readme.txt'
rsync – preserves special characters in transfers
rsync is useful for transferring files without losing special characters like spaces and asterisks in filenames:
rsync -av /src/ 'important file*.txt' /backup/
