md5sum output only hash in file

Question

hi I want to create a bash file on linux, which checks the md5 hash of a file against a backup md5 hash, so i know if the original file has been tampered with. The script should output the md5 hash of two files and than compare the two created hash files:

md5sum file1 > file1.md5 | cut -c -32
if [ file1.md5 =! backup.md5 ] then;
   #send email

but it does not work, there is still the filename in the file.md5, has someone an idea on how to only get the has to the file.md5?

Answer 1

There are several issues with your script.

First you apply cut -c -32 after you have redirected the md5sum output to file1.md5 already, which is why it does nothing.

You should restructure it like that, instead:

md5sum file1 | cut -c -32 > file1.md5

Next, you can not really compare files with =! directly, you have to read and compare their content instead, like this:

[ "$(cat file1.backup.md5)" != "$(cat file1.real.md5)" ]

Also note that md5sum does already have a "check mode", so you can simply do this:

#Save MD5 sum of your file to backup.md5, in md5sum native format
md5sum file1 > backup.md5

#Later on ...
if ! md5sum -c backup.md5; then
...

Answer 2

You have the wrong order of the commands. Write the

md5sum file1 | cut -c -32 > file1.md5