PEM-encoded private keys are multi-line text blobs that start with the line
-----BEGIN <x> PRIVATE KEY-----
and end with the line
-----END <x> PRIVATE KEY-----
The following variation is also possible:
-----BEGIN PRIVATE KEY-----
[...]
-----END PRIVATE KEY-----
Sample PEM private key
-----BEGIN RSA PRIVATE KEY-----
Proc-Type: 4,ENCRYPTED
DEK-Info: AES-128-CBC,C0E84534BAD040A56EB8AC779018C550
IY6Exvhzc7JZB0MtVr/qyRUZq8iChUvmCyoc5Vxuo/vhWZogBnIevPVycfPaV70j
vmkB5YDU/UpvSXfJ1ReQNL8uRCZplr7Sk1VbSy0Q3qSaXZOo6qf1z/d2FjakFdYE
BqjiEJ1eJ/ybViyDJTaZgRNFlex7JxrygX004AMooIFRAl2iN5A/nj6JKZBQY8//
ABqZ7+mrF1rVstHKsqTlCts0rTkGHk3+CtFJi6GNk6v0ZhM5RdTq6Dru/eQi/BIN
8qVZF47/7EOl60IItmh/oon271tel5ewFOLcb1w315ZC422q6Xk+n++6dLP238R4
1tig/K4d819oCL9JrySd9p4lows4CLMNGm7K3aNonxAzX62mdcG7fj9uMgzgFlCb
9/ZSS6b2sHNc2roz2w9sLCegrImRGE6/oSyHxhpgtjOncUETaeCVr9aw3wyMuys9
kaaih7HQyalrDYw90ExRXedAbrtsshYoqfvERXsteFdogKNhqDGRtxg2eVJgYUIx
S0Pdwl8jVL5nVobXiKaNqZAxOv7+ReXHvjOygalIDiJGajagQM6p0s2j+CNH9ZUv
ovcqkKnvaO0cEoDpsLWrIi+nXnyXV07TwSxsTOCaQzg3t/+9BJ/vuLpJjl6tUZbh
z3lMdEt+mq1IUcoASbfzqMoRSgcYZtg61moBCK1UPB8IV8bozW5K0qJAzuBpvjte
GrsT/4yFPl6Fx5T5y0+GJ06EM6dGBd8t4xYDx6Ca0ncbWnS3VtU2uNLKSZ7GMdgk
7tRfNF8uO7P7r6xS0+ZuRL3ShLunVvz/INF78dELGrVe7rgrXt+AHTgL/mjKQj5z
jZp/knAG5syTNf0KXabIG6rz8AkY5X7med2rEzuzSoNhzaJyiivAL/Ri0Mu2SU8Z
r6VMchcYn1sGZkMZFTHH1DoNeCLh64Il/gq9CvqBJBbR7g+S6SYMrxc3n4sqopti
Cb+AEgeYX4wq7Smeu7dvGEoQu5qMCzCscs6+okb6on4fOO7nWcD0icBFEToB+nEK
LAkxxXGmdw1E+YTE4bHSH3RAgyywMASaLdExALav1R6tbI/SGx9+PLPmJzV/Ygpv
O3OP9xoy2xiGXt18JvOI2NOEzJZnOId9n2I1rJvntuLm6tB+KHsfJ822CSBvaYSC
1IRWOU0ViJuPtgPg661CH+gzG+M9Cqdt5R2AqbAHu4w4/6hR6V21IJSAPrFll4YB
Eg4zgfAFA53pTfpm6tE+avbWpg8f3G/i7LS5CSAA79cf5a4ziGyGgrZYA631Bnpk
ZHfVrAOP7Ulgx2l9iAAbhPwaext89ENOTK/k0g43X3ypmRVnqmvbWQ5LdFtBIr1Q
DVsCkxud3qu4aXniEzB+q8kzCsOw4hsuUzB3PK9Ai7h7BkxfTsPNsA3vHfgzfK+U
1VZ9Fu3Jd/9qO5gdl7h8aQZEagIZ84rrvJFcilHY53F8Q67fHp6EDtlCMeIh8zb5
KO/35JWqN5q51MGLpWdMd8um3JcikyryDoKO/3gl6okny9na3XsXB7b72eH9hKtm
DmEWQ1PB4Gha66/r7WW/1pNKk0jUCEyuBW6nZeZjeyZcOVd2Gtz1juKbCwr9F+tE
-----END RSA PRIVATE KEY-----