How to remove unprintable characters from a file

cat <file> | tr -dc '[\011\012\015\040-\176]'

Creating a PEM format ssh credentials file

ssh-keygen

openssl rsa -in ./id_rsa -outform pem > ./id_rsa.pem

PAM: a simple RGB+ALPHA file format

To create images with transparencies without too much scaffolding, use the netpgm-associated format PAM, and then use pamtotiff.

#include 

int main() {
    
    printf("P7\n");
    printf("WIDTH 256\n");
    printf("HEIGHT 256\n");
    printf("DEPTH 4\n");
    printf("MAXVAL 255\n");
    printf("TUPLTYPE RGB_ALPHA\n");
    printf("ENDHDR\n");

    unsigned int row,col;
    for (row=0; row<256; row++) {
    for (col=0; col<256; col++) {
        
        printf("%c", (char)col);         // RED
        printf("%c", (char)(255-col));   // GREEN
        printf("%c", (char)row);         // BLUE
        printf("%c", (char)(255-row));   // OPACITY

    }}
    
    return 0;

}

Changing the location specified by java.io.tmpdir before running a Java program

On some systems, java.io.tmpdir is hard-coded to /tmp/. This can be changed with, e.g.:

export _JAVA_OPTIONS=-Djava.io.tmpdir=/mnt/tmp/whatever

Change a running process to nohup

1. put the process in the background (CTRL-Z)
2. make sure it's still running though (bg)
3. run disown -h

This doesn't really change to nohup, but it does prevent the job from receiving the SIGHUP signal when you exit the shell. Use the -a option to affect all jobs.

According to http://linux.about.com/library/cmd/blcmdl1_disown.htm:

disown [-ar] [-h] [jobspec ...]
    Without options, each jobspec is removed from the table of active jobs. If the -h option is given, each jobspec is not removed from the table, but is marked so that SIGHUP is not sent to the job if the shell receives a SIGHUP. If no jobspec is present, and neither the -a nor the -r option is supplied, the current job is used. If no jobspec is supplied, the -a option means to remove or mark all jobs; the -r option without a jobspec argument restricts operation to running jobs. The return value is 0 unless a jobspec does not specify a valid job.

Sending attachments from a command line with uuencode

The arguments to uuencode are the file, and the name of the file as it appears in the attachment. I would usually use the same string so I don't have to remember the order.

uuencode file.jpg file.jpg | mail -s 'subject' keith@foosball.com

Using GnuPG (gpg) for simple file encryption

How to use GnuPG for simple cases.

1. Install gpg, e.g.,

   sudo port install gnupg

2. Create a public/private key for yourself, e.g.,

   gpg --gen-key

   (you will have to answer some questions, I used 'knoto' as my comment
3. Encrypt a file, e.g.,

   gpg -e -r knoto myfile.foo

   (creates myfile.foo.gpg that can only be decrypted by knoto).