The login Process
The first line tells the kernel how to run this program, in this case by letting the bash shell interpret it. The first exec line is a Bourne shell trick that lets a shell script change the source/destination of its standard input, standard output and standard error. We want to set file descriptors 0, 1 and 2 to refer to the terminal device as expected by login (and many other programs) when they run. The cat command displays the system's standard logon message. The shift command shifts the positional parameters to the shell script. Argument $1 is deleted, argument $2 becomes $1, argument $3 becomes $2 and so on. The last line executes the rest of the command line as a program. In this case, the login -f option performs the normal login procedure, with the -f option telling login not to bother with passwords.
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