The sendmail program's ability to perform different tasks necessitates that the command line be processed in steps.
The command line is prescanned to set its -d debugging switch. That switch allows you to watch all the steps taken by sendmail prior to processing the rest of the command-line switches.
Internal sendmail macros are given their starting values, then the command line's argv (the name used to run sendmail) is processed. That name can determine the sendmail program's mode of operation.
The command-line switches are processed. Although the configuration file is read after the command line is processed, options in the command line (with -o and -O) still supersede those in the configuration file.
The configuration file is read.
If sendmail is running in a mode that allows it to verify or deliver to recipients, the remainder of the command line is processed to extract the recipient list.
When sendmail begins to run, it performs a preliminary scan of its command-line arguments. It does this because some actions need to be performed before the configuration file is read. The -d command-line switch is processed during the prescanning phase.
After the command-line switches are prescanned, but before they are processed in full, sendmail performs two important internal tasks.
The environment variables that are given to sendmail when it is first run are ignored. When running delivery agents, sendmail provides a small, customized environment. See Section 10.2 for a detailed discussion of this step.
Certain sendmail macros are next declared and assigned values. The $w macro ($w), $j macro ($v), and $=w class macro ($=w) are given values that identify the current host. The $m macro ($m) is given a value that is the local domain name. The $k macro ($k) and the $=k class ($=k) are also given values at this time. The $v macro ($v) is assigned a value that is the current version of the sendmail program. The $b macro ($b) is given the current date and time as its value.
Command-line switches are processed by sendmail as they appear in the command line, from left to right. The processing of switches ends when an argument is found that lacks a leading - character, or, beginning with V8, when a -- argument is found.
The fact that the configuration file is read after the command-line switches are processed can lead to some confusion. Some, but not all, command-line switches can overwrite some configuration file commands. Because there is no general rule, we describe the behavior of each item (such as macros and options) in a chapter dedicated to each.
The final step sendmail undertakes in processing its command line is gathering the list of recipients. Each recipient (or list of recipients if more than one is contained in a single command-line argument) is fully processed for delivery, and any error messages are printed before delivery is actually undertaken.
If sendmail is running in a mode that doesn't require recipients, any list of recipients in the command line is silently ignored.