Only get hash value using md5sum (without filename)

Question

I use md5sum to generate a hash value for a file. But I only need to receive the hash value, not the file name.

md5=`md5sum ${my_iso_file}`
echo ${md5}

Output:

3abb17b66815bc7946cefe727737d295  ./iso/somefile.iso

How can I 'strip' the file name and only retain the value?

Solution 1

Using AWK:

md5=`md5sum ${my_iso_file} | awk '{ print $1 }'`

Solution 2

A simple array assignment works... Note that the first element of a Bash array can be addressed by just the name without the [0] index, i.e., $md5 contains only the 32 characters of md5sum.

md5=($(md5sum file))
echo $md5
# 53c8fdfcbb60cf8e1a1ee90601cc8fe2

Solution 3

You can use cut to split the line on spaces and return only the first such field:

md5=$(md5sum "$my_iso_file" | cut -d ' ' -f 1)

Solution 4

On Mac OS X:

md5 -q file

Solution 5

md5="$(md5sum "${my_iso_file}")"
md5="${md5%% *}" # remove the first space and everything after it
echo "${md5}"

View more solutions

Comments

[Sridhar Sarnobat]

Very surprising this isn't an option for md5sum.

[TommyAutoMagically]

Agreed! Why isn't this an option? Can a GNU-Master shed some light?

[Magnetic_dud]

Why do you need to have a "only hash" flag when you can trim the result with some regex? (I am sarcastic)

[Roman Cheplyaka]

Nice. One note -- on the first line you don't need quotes around $() (although they do no harm) but certainly need them around ${}.

[Gordon Davisson]

@Roman: yeah, I tend to habitually quote any expansion (unless there's a reason not to) -- it's easier than keeping track of the cases where it's safe to skip the quotes. (Although in this case, I left them off the actual filename... stand by for an edit.)

[jyz]

Awesome. Just one question, I know the question is tagged bash, but can you tell me if array is a bash only feature or some shell standard?

[Christophe De Troyer]

Or md5=`md5sum < ${my_iso_file}` However this still outputs " - " at the end. But for comparisons this should be enough.

[Andy]

the first line doesn't work inside the do section of a for loop...as a Bash newb I don't yet know why

[Peter.O]

@Andy: If you try this line of code (in the terminal, or in a script): echo>file; for i in file; do md5=($(md5sum file)); echo $md5; done - It should output 68b329da9893e34099c7d8ad5cb9c940

[Andy]

@Peter.O that does, I figured out that the problem was I had #!/bin/sh at the top of my script instead of #!/bin/bash. Thanks!

[lkraav]

How come echo ($(echo -n foo | md5sum)) doesn't work? Errors out bash: syntax error near unexpected token $(echo -n foo | md5sum)'

[Peter.O]

@lkraav: The command echo -n foo | md5sum outputs 2 shell words to stdout: acbd18db4cc2f85cedef654fccc4a4d8 and - (the - indicates the source as stdin). – You must tell bash to capture those words into a string, using Command Substitution: $( command ). – The ( brackets ) produce a bash array with 2 elements. However, you must assign that array construct ( … ) to an variable name; hence, using md5 as the array name: md5=($(echo -n foo | md5sum)). You haven't assigned the array to a variable name

[Shane]

This is a bash question, but note that this doesn't work in zsh. Instead you can echo $md5[1] to get only the hash (but this isn't portable to bash)...

[Sridhar Sarnobat]

doesn't work on my Mac OS X 10.7. But thanks for posting, for whatever version this works on.

[alper]

Wrong it gives following output on Mac MD5 (/Users/hello.txt) = 24811012be8faa36c8f487bbaaadeb71 and your code returns MD5.

[alper]

You can get run of - by adding | awk '{print $1}' end of your code => md5sum < ${my_iso_file} | awk '{print $1}' @ChristopheDeTroyer

[David Tabernero M.]

@CzarekTomczak True, but just by using this answer's method, you could reuse it with different hashing algorithms just by changing the command itself. md5sum -> sha256sum without remembering what amount of characters you need to "cut".

[Anton Tarasenko]

Also gmd5sum from coreutils would work on MacOS like md5sum in other answers mentioned here.

[mgutt]

SO: Searching how to create a md5 hash of a file, learning the shortcut access of the first array element. Thanks :)

[Stepan Kolesnik]

To make the script a bit more bulletproof make sure to set IFS explicitly in case it is set to some non-standard value: IFS=" " md5=($(md5sum file))

[scrutari]

This is a nice solution, but it doesn't work in Jenkins

[MoonCactus]

Why capture? You can simply delete the space and what is behind: sed 's: .*::' does the same thing!

[Peter Mortensen]

The question is tagged with Bash, but perhaps indicate how much of this is Bash-specific (e.g., would it work in Z shell (now allegedly the default shell in macOS v10.15 (Catalina) and later)).

[Jhoan Manuel Muñoz Serrano]

It worked for me on version 11.5.2 but after removing the -q option

[Cameron Hudson]

md5 is different from md5sum, which is what OP asked about.