Using md5deep

md5deep -r path/to/dir > sums.md5

Using find and md5sum

find relative/path/to/dir -type f -exec md5sum {} + > sums.md5

Be aware, that when you run check on your MD5 sums with md5sum -c sums.md5, you need to run it from the same directory from which you generated sums.md5 file. This is because find outputs paths that are relative to your current location, which are then put into sums.md5 file.

If this is a problem you can make relative/path/to/dir absolute (e.g. by puting $PWD/ in front of your path). This way you can run check on sums.md5 from any location. Disadvantage is, that now sums.md5 contains absolute paths, which makes it bigger.

Fully featured function using find and md5sum

You can put this function to your .bashrc file (located in your $HOME directory):

function md5sums {  if [ "$#" -lt 1 ]; then    echo -e "At least one parameter is expected\n" \            "Usage: md5sums [OPTIONS] dir"  else    local OUTPUT="checksums.md5"    local CHECK=false    local MD5SUM_OPTIONS=""    while [[ $# > 1 ]]; do      local key="$1"      case $key in        -c|--check)          CHECK=true          ;;        -o|--output)          OUTPUT=$2          shift          ;;        *)          MD5SUM_OPTIONS="$MD5SUM_OPTIONS $1"          ;;      esac      shift    done    local DIR=$1     if [ -d "$DIR" ]; then  # if $DIR directory exists      cd $DIR  # change to $DIR directory      if [ "$CHECK" = true ]; then  # if -c or --check option specified        md5sum --check $MD5SUM_OPTIONS $OUTPUT  # check MD5 sums in $OUTPUT file      else                          # else        find . -type f ! -name "$OUTPUT" -exec md5sum $MD5SUM_OPTIONS {} + > $OUTPUT  # Calculate MD5 sums for files in current directory and subdirectories excluding $OUTPUT file and save result in $OUTPUT file      fi      cd - > /dev/null  # change to previous directory    else      cd $DIR  # if $DIR doesn't exists, change to it to generate localized error message    fi  fi}

After you run source ~/.bashrc, you can use md5sums like normal command:

md5sums path/to/dir

will generate checksums.md5 file in path/to/dir directory, containing MD5 sums of all files in this directory and subdirectories. Use:

md5sums -c path/to/dir

to check sums from path/to/dir/checksums.md5 file.

Note that path/to/dir can be relative or absolute, md5sums will work fine either way. Resulting checksums.md5 file always contains paths relative to path/to/dir.You can use different file name then default checksums.md5 by supplying -o or --output option. All options, other then -c, --check, -o and --output are passed to md5sum.

First half of md5sums function definition is responsible for parsing options. See this answer for more information about it. Second half contains explanatory comments.

How about:

find /path/you/need -type f -exec md5sum {} \; > checksums.md5

Update#1: Improved the command based on @twalberg's recommendation to handle white spaces in file names.

Update#2: Improved based on @jil's suggestion, to remove unnecessary xargs call and use -exec option of find instead.

Update#3: @Blake a naive implementation of your script would look something like this:

#!/bin/bash# Usage: checksumchecker.sh <path>find "$1" -type f -exec md5sum {} \; > "$1"__checksums.md5

Updated Answer

If you like the answer below, or any of the others, you can make a function that does the command for you. So, to test it, type the following into Terminal to declare a function:

function sumthem(){ find "$1" -type f -print0 | parallel -0 -X md5 > checksums.md5; }

Then you can just use:

sumthem /Users/somebody/somewhere

If that works how you like, you can add that line to the end of your "bash profile" and the function will be declared and available whenever you are logged in. Your "bash profile" is probably in $HOME/.profile

Original Answer

Why not get all your CPU cores working in parallel for you?

find . -type f -print0 | parallel -0 -X md5sum

This finds all the files (-type f) in the current directory (.) and prints them with a null byte at the end. These are then passed passed into GNU Parallel, which is told that the filenames end with a null byte (-0) and that it should do as many files as possible at a time (-X) to save creating a new process for each file and it should md5sum the files.

This approach will pay the largest bonus, in terms off speed, with big images like Photoshop files.