15.2 Command-Line Switches

Command-line switches are command-line arguments that begin with a - character, and precede the list of recipients (if any). The forms for command-line switches, where X is a single letter, are:

-X         Boolean switch 
-Xarg      switch with argument 

All switches are single letters. The complete list is shown in Table 15-2.

Some switches are called Boolean because they are either true or false. The -v switch, for example, is Boolean because it puts sendmail into verbose mode if it is present (true). If it is absent (false), sendmail does not run in verbose mode.

Some switches take arguments. The -C switch, for example, tells sendmail where to find its configuration file. When a switch takes an argument, the argument can immediately follow the letter or be separated from it with whitespace:^[2]

^[2] Prior to V8 sendmail, whitespace was not allowed between the letter and the argument.

-Ctest.cf      good
-C test.cf     also good

The only exceptions to this rule are the -d command-line switch (set debugging mode) and the -q command-line switch (enter queue mode). They cannot have whitespace between the letter and the arg.

Some switches, such as -q (process the queue), can either be Boolean or take an argument:

-q             Boolean
-q1h           with argument

The position of switches in the command line is critical. If any follow the list of recipients, they are wrongly taken as mail addresses and lead to bounced mail. But the order in which switches appear prior to the recipients is not important. That is, they can appear in any order without changing the behavior of sendmail.

An undefined switch letter causes the following error to be printed and sendmail to immediately exit:

sendmail: illegal option -- bad letter here

The special switch -- can be used to delimit the switches from the list of recipients:

% /usr/sbin/sendmail -- -jim

Here, the recipient is -jim. To prevent the - of -jim from being wrongly interpreted as indicating a switch, the special switch -- is used to mark the end of all switches.^[3]

^[3] Under pre-V8 sendmail, recipient names could never begin with a -C, -b, -d, -q, or -Z. If any did, they were wrongly interpreted as switches during preprocessing.