md5.md

md5

Calculate md5sum of a string or stream.

Usage

$ help md5
md5: md5 [string]
    Calculate MD5 sum.
    
    Calculates the MD5 sum of the string argument, or stdin if no
    argument is provided. The result is assigned to the REPLY 
    variable.

Examples

Calculate MD5 sum of a string

md5 ''
printf 'MD5 sum of the empty string is: %s\n' "$REPLY"
## Output:
#MD5 sum of the empty string is: d41d8cd98f00b204e9800998ecf8427e

md5 $'hello\n'
printf 'MD5 sum of hello<LF> is: %s\n' "$REPLY"
## Output:
#MD5 sum of hello<LF> is: b1946ac92492d2347c6235b4d2611184

Calculate MD5 sum of a stream/file

md5 < /dev/null
printf 'MD5 sum of /dev/null is: %s\n' "$REPLY"
## Output:
#MD5 sum of /dev/null is: d41d8cd98f00b204e9800998ecf8427e

md5 <<< hello
printf 'MD5 sum of hello<LF> is: %s\n' "$REPLY"
## Output:
#MD5 sum of hello<LF> is: b1946ac92492d2347c6235b4d2611184

Implementation notes

This was the first builtin I attempted. It was triggered by me solving the Advent of Code challenges using multiple languages, including bash. The one requiring calculating ~1M md5 sums took ages when each one required forking and execing md5sum(1) or md5(1). So I decided to try writing a loadable builtin, and learn a bit about how an md5sum is calculated in the process.

I wrote it by reading the specs of the RFC, then when it finally produced correct results, I split it up into multiple functions, similar to how BSD had split them up. The current source can probably be optimized a bit, but the speed gain over forking and execing an external executable is large enough.