Classic Shell Scripting

The Password Files

Let's call our two hypothetical Unix systems u1 and u2. Example 11-1 presents the /etc/passwd file from u1.^[2]

Example 11-1. u1 /etc/passwd file

root:x:0:0:root:/root:/bin/bash
bin:x:1:1:bin:/bin:/sbin/nologin
daemon:x:2:2:daemon:/sbin:/sbin/nologin
adm:x:3:4:adm:/var/adm:/sbin/nologin
tolstoy:x:2076:10:Leo Tolstoy:/home/tolstoy:/bin/bash
camus:x:112:10:Albert Camus:/home/camus:/bin/bash
jhancock:x:200:10:John Hancock:/home/jhancock:/bin/bash
ben:x:201:10:Ben Franklin:/home/ben:/bin/bash
abe:x:105:10:Honest Abe Lincoln:/home/abe:/bin/bash
dorothy:x:110:10:Dorothy Gale:/home/dorothy:/bin/bash

And Example 11-2 presents /etc/passwd from u2.

Example 11-2. u2 /etc/passwd file

root:x:0:0:root:/root:/bin/bash
bin:x:1:1:bin:/bin:/sbin/nologin
daemon:x:2:2:daemon:/sbin:/sbin/nologin
adm:x:3:4:adm:/var/adm:/sbin/nologin
george:x:1100:10:George Washington:/home/george:/bin/bash
betsy:x:1110:10:Betsy Ross:/home/betsy:/bin/bash
jhancock:x:300:10:John Hancock:/home/jhancock:/bin/bash
ben:x:301:10:Ben Franklin:/home/ben:/bin/bash
tj:x:105:10:Thomas Jefferson:/home/tj:/bin/bash
toto:x:110:10:Toto Gale:/home/toto:/bin/bash

If you examine these files carefully, you'll see they represent the various possibilities that our program has to handle:

• Users for whom the username and UID are the same on both systems. This happens most typically with administrative accounts such as root and bin.

• Users for whom the username and UID exist only on one system but not the other. In this case, when ...