Okay, the user wants to know how to make ssh-keygen output a decrypted version of a private key to another file. Let me think about how ssh-keygen works.

First, when you generate an SSH key with ssh-keygen, it typically creates a private key and a public key. The private key is usually encrypted with a passphrase for security. If the user has an existing encrypted private key and wants to decrypt it, they need to remove the passphrase.

So, the process would involve using ssh-keygen again to change the passphrase. By setting an empty passphrase, the private key becomes decrypted. The command would be something like ssh-keygen -p, then specifying the input file (the encrypted key) and the output file for the decrypted version. Let me check the exact syntax.

Yes, the command should be:

ssh-keygen -p -f encrypted_key -N '' -m pem -P old_passphrase

Wait, but the user might not know the original passphrase. They need to input the current passphrase if the key is encrypted. If they don't provide it, ssh-keygen will prompt them. But in the command line, they can specify it with -P for the old passphrase. If they want to script it, they need to include -P, but if it's interactive, they can omit it.

Also, specifying the -m pem is important if the key is in the new OpenSSH format, which isn't compatible with older versions. Converting it to PEM ensures it's in the traditional format, which might be necessary for some applications. But maybe the user just wants the decrypted version in the same format. Hmm.

Wait, the default for ssh-keygen when writing private keys is the OpenSSH format. If the user wants to ensure compatibility or just get the decrypted key without changing the format, maybe omitting -m pem is okay. But sometimes when modifying keys, using PEM is more straightforward. I should mention that.

So the steps are: use ssh-keygen -p to change the passphrase. Specify the input file with -f, the old passphrase with -P (if needed), and the new passphrase with -N ''. The output will be written to the same file unless an output file is specified. Wait, does ssh-keygen allow specifying a different output file when changing the passphrase? Let me check the man page.

Looking at the ssh-keygen man page, the -p option is for changing the passphrase of a private key. The -f option specifies the filename. However, the output is written back to the same file. So how can we direct the decrypted key to a different file?

Ah, right. If you want to keep the original encrypted key and have a decrypted version in another file, you can't do it directly with a single ssh-keygen command. Because when you run ssh-keygen -p, it modifies the original file. So to get a decrypted copy, you need to first make a copy of the encrypted key, then decrypt the copy, which would leave the original intact and the decrypted version in the new file.

Alternatively, you can use ssh-keygen to convert the key to a different format and output to a new file. For example, converting from OpenSSH format to PEM might allow writing to a new file. Let's see.

Another approach: using the -e and -m options. Wait, no. -e is for exporting to a different public key format. Maybe using the -m option when generating. Wait, when changing the passphrase, the -m option specifies the key format. If the original key is in OpenSSH format (starts with BEGIN OPENSSH PRIVATE KEY), converting it to PEM (BEGIN RSA PRIVATE KEY) might require using -m PEM.

So, the command would be:

ssh-keygen -p -f encrypted_key -m pem -N '' -P old_passphrase

But this modifies the original file. To avoid that, the user should copy the encrypted key to a temporary file, decrypt the copy, and then maybe rename it. Or perhaps use a pipe. Hmm.

Alternatively, use a combination of ssh-keygen to change the passphrase and output to stdout, then redirect to a file. But ssh-keygen doesn't support outputting the private key to stdout for security reasons. So that might not be possible.

Wait, let me test. If I run ssh-keygen -p -f id_rsa -N '' -P oldpass, it will overwrite id_rsa. So to create a new file, I need to first copy the encrypted key to a temporary file, run ssh-keygen on the temp file, then move it to the desired output. For example:

cp encrypted_key temp_key

ssh-keygen -p -f temp_key -N '' -P old_passphrase

mv temp_key decrypted_key

This way, the original encrypted_key remains, and decrypted_key is the decrypted version. But this requires using temporary files and multiple steps. Maybe that's the way to go.