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0. Don't reinvent the wheel

   There could already exist some tool for doing what you need.

1. Check your history files

   grep mycommand .*history
   

2. Don't use command line arguments or environment variables to store sensible datas (like password)!

   Always use fd (file descriptors)! Try

   ps axefwww
   

   to read all command lines and environment, currently running on your host

From openssl's man page:

(where sensible datas as command line argument or environment variables are recommended to be used where security is not important and with caution)

   Pass Phrase Options
       Several commands accept password arguments, typically using -passin and
       -passout for input and output passwords respectively. These allow the
       password to be obtained from a variety of sources. Both of these
       options take a single argument whose format is described below. If no
       password argument is given and a password is required then the user is
       prompted to enter one: this will typically be read from the current
       terminal with echoing turned off.

       pass:password
           The actual password is password. Since the password is visible to
           utilities (like 'ps' under Unix) this form should only be used
           where security is not important.

       env:var
           Obtain the password from the environment variable var. Since the
           environment of other processes is visible on certain platforms
           (e.g. ps under certain Unix OSes) this option should be used with
           caution.

       file:pathname
           The first line of pathname is the password. If the same pathname
           argument is supplied to -passin and -passout arguments then the
           first line will be used for the input password and the next line
           for the output password. pathname need not refer to a regular file:
           it could for example refer to a device or named pipe.

       fd:number
           Read the password from the file descriptor number. This can be used
           to send the data via a pipe for example.

       stdin
           Read the password from standard input.