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`affirm`

Determine the Boolean value of a set of arguments.

Synopsis

affirm [-a | -o] [-s] [string1 [string2...]]

affirm tests its arguments for truth or falsehood. The arguments can be of the form true/false, t/f, yes/no, y/n, on/off, 1/0 and are case insensitive. It will print either true or false on stdout with a status return to match.

Options

-a: Produce the logical AND of all arguments (default).
-o: Produce the logical OR of all arguments.
-s: Work silently, just producing the exit status.

Notes

The -a option returns immediately if it encounters a false argument; remaining arguments are not checked for validity. It can best be thought of as searching for a false argument. Even if the argument list contains an unrecognized value the search still continues for a false value. If none is found and there were no unrecognized arguments then it returns true.
The -o option behaves similarly except that it searches for a true argument. Hence, to test the logical value of an environment variable which may be undefined use
affirm -a $VAR
(or just affirm $VAR) to get a true result if VAR is blank, and use
affirm -o $VAR
to get a false result if VAR is blank.
The -a and -o options may be used together, for example:
affirm -o $V1 $V2 -a $V3 $V4
returns true if either of V1 or V2 is true, or if V3 and V4 are both true or both blank.

Diagnostics

Status return values reflect a true or false result, or invokation error
0: true
1: false
2: unrecognized argument

Examples

To test an aipsrc (p) resource setting (Bourne shell):

   ENABLED=`affirm -a \`getrc inhale.base.code.preserve 2> /dev/null\``

Sets ENABLED to true if the inhale.base.code.preserve was set to some variant of the affirmative, or if it was not defined. To get a false value by default the -o option could have been used instead.

Author

Original: 1993/09/01 by Mark Calabretta, ATNF

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