When working with file operations in Bash, a common question arises: is wildcard expansion guaranteed to follow alphabetical order? This becomes particularly important when dealing with split files that need to be processed in sequence.

According to Bash documentation and POSIX standards, wildcard expansion (*) sorts files lexicographically (alphabetically) by default. This means BigFilePiece.aa will always come before BigFilePiece.ab in the expansion.

# Example showing sorted expansion
$ touch BigFilePiece.{ab,aa,ac}
$ echo BigFilePiece.*
BigFilePiece.aa BigFilePiece.ab BigFilePiece.ac

While alphabetical order is the default, there are scenarios where this might not hold:

• If the LC_COLLATE environment variable is set to non-standard values
• When using shell options like nocaseglob or nullglob
• In shells other than Bash (though most follow similar behavior)

The performance impact of using cat to concatenate files is generally negligible for most use cases. Modern systems can handle this operation efficiently:

# Benchmark example
$ time cat BigFilePiece.* > /dev/null
real    0m0.003s
user    0m0.001s
sys     0m0.002s

For absolute certainty in file ordering, consider these alternatives:

# Explicit sorting
cat $(ls BigFilePiece.* | sort)

# Using numbered suffixes
split -d -b 10485760 Big.file BigFilePiece.

To ensure reliable operation:

1. Use the -d flag with split for numeric suffixes
2. Set LC_COLLATE=C for consistent sorting
3. Test your specific environment with sample files

When working with file processing in Bash, it's crucial to understand how wildcard expansion orders the resulting filenames. The default behavior in Bash (and most shells) is to expand wildcards like * in lexicographical (alphabetical) order based on the current locale's collation sequence.

This means that when you use:

cat BigFilePiece.*

The files will be processed in order like:

BigFilePiece.aa
BigFilePiece.ab
BigFilePiece.ac
...
BigFilePiece.zz

You can easily verify this behavior with a simple test:

touch file_{a,b,c,d,aa,ab,ac}
echo *
# Output shows: file_a file_aa file_ab file_ac file_b file_c file_d

While alphabetical order is the default, it's important to note that this is locale-dependent. To ensure consistent behavior across systems, you can set:

export LC_ALL=C

This forces traditional byte-value ordering, which gives predictable results for ASCII characters.

The performance cost of using cat to combine files is negligible for most use cases. The command simply:

1. Opens each file in sequence
2. Streams the contents to stdout
3. Closes each file

There's no in-memory concatenation or temporary files involved.

For absolute certainty in file ordering, you could:

cat $(ls BigFilePiece.* | sort)

Or using process substitution:

cat <(printf '%s\n' BigFilePiece.* | sort)

If dealing with thousands of split files, you might want to:

find . -name "BigFilePiece.*" -print0 | sort -z | xargs -0 cat | bigFileProcessor

This handles filenames with spaces and special characters safely.