sendmail, 4th Edition

Write a Delivery Agent Script

The program that is driven by the prog delivery agent can be a compiled executable binary, a shell script, or even a perl(1) script. The limitation on the kind of program that can be run is made by the sh(1) shell (if sh -c is used in the A=) or by execve(2) (if it is launched directly from the P=). You need to read the manuals on your system to determine your limitations. For example, not all versions of sh(1) allow constructs such as the following in scripts:

#!/usr/local/bin/perl

When this appears as the first line of a script, the #! tells sh(1) or execve(2) to run the program whose pathname follows, to execute the commands in the script.^[201]

In writing a program for mail delivery using the prog delivery agent, some unexpected problems can arise. We will illustrate, using fragments from a Bourne shell script.

^{[201] *} Not all versions of Unix support this feature, and on some of those that do support it, only a few shells are supported.