Question

Problem Specification:

Given a directory, I want to iterate through the directory and its non-hidden sub-directories,
 and add a whirlpool hash into the non-hidden
file’s names.
If the script is re-run it would would replace an old hash with a new one.

<filename>.<extension>   ==>  <filename>.<a-whirlpool-hash>.<extension>

<filename>.<old-hash>.<extension>   ==>  <filename>.<new-hash>.<extension>

Question:

a) How would you do this?

b) Out of the all methods available to you, what makes your method most suitable?

Verdict:

Thanks all, I have chosen SeigeX’s answer for it’s speed and portability.
It is emprically quicker than the other bash variants,
 and it worked without alteration on my Mac OS X machine.

Answer 1

Updated to fix:

1. File names with ‘[‘ or ‘]’ in their name (really, any character now. See comment)
2. Handling of md5sum when hashing a file with a backslash or newline in its name
3. Functionized hash-checking algo for modularity
4. Refactored hash-checking logic to remove double-negatives

#!/bin/bash
if (($# != 1)) || ! [[ -d "$1" ]]; then
    echo "Usage: $0 /path/to/directory"
    exit 1
fi

is_hash() {
 md5=${1##*.} # strip prefix
 [[ "$md5" == *[^[:xdigit:]]* || ${#md5} -lt 32 ]] && echo "$1" || echo "${1%.*}"
}

while IFS= read -r -d $'\0' file; do
    read hash junk < <(md5sum "$file")
    basename="${file##*/}"
    dirname="${file%/*}"
    pre_ext="${basename%.*}"
    ext="${basename:${#pre_ext}}"

    # File already hashed?
    pre_ext=$(is_hash "$pre_ext")
    ext=$(is_hash "$ext")

    mv "$file" "${dirname}/${pre_ext}.${hash}${ext}" 2> /dev/null

done < <(find "$1" -path "*/.*" -prune -o \( -type f -print0 \))

This code has the following benefits over other entries thus far

• It is fully compliant with Bash versions 2.0.2 and beyond
• No superfluous calls to other binaries like sed or grep; uses builtin parameter expansion instead
• Uses process substitution for ‘find’ instead of a pipe, no sub-shell is made this way
• Takes the directory to work on as an argument and does a sanity check on it
• Uses $() rather than “ notation for command substitution, the latter is deprecated
• Works with files with spaces
• Works with files with newlines
• Works with files with multiple extensions
• Works with files with no extension
• Does not traverse hidden directories
• Does NOT skip pre-hashed files, it will recalculate the hash as per the spec

Test Tree

$ tree -a a
a
|-- .hidden_dir
|   `-- foo
|-- b
|   `-- c.d
|       |-- f
|       |-- g.5236b1ab46088005ed3554940390c8a7.ext
|       |-- h.d41d8cd98f00b204e9800998ecf8427e
|       |-- i.ext1.5236b1ab46088005ed3554940390c8a7.ext2
|       `-- j.ext1.ext2
|-- c.ext^Mnewline
|   |-- f
|   `-- g.with[or].ext
`-- f^Jnewline.ext

4 directories, 9 files 

Result

$ tree -a a
a
|-- .hidden_dir
|   `-- foo
|-- b
|   `-- c.d
|       |-- f.d41d8cd98f00b204e9800998ecf8427e
|       |-- g.d41d8cd98f00b204e9800998ecf8427e.ext
|       |-- h.d41d8cd98f00b204e9800998ecf8427e
|       |-- i.ext1.d41d8cd98f00b204e9800998ecf8427e.ext2
|       `-- j.ext1.d41d8cd98f00b204e9800998ecf8427e.ext2
|-- c.ext^Mnewline
|   |-- f.d41d8cd98f00b204e9800998ecf8427e
|   `-- g.with[or].d41d8cd98f00b204e9800998ecf8427e.ext
`-- f^Jnewline.d3b07384d113edec49eaa6238ad5ff00.ext

4 directories, 9 files