A file specified as an option-argument to the -m or -M options
shall contain one position-sensitive test per line, which shall
be applied to the file. If the test succeeds, the message field
of the line shall be printed and no further tests shall be
applied, with the exception that tests on immediately following
lines beginning with a single '>' character shall be applied.
Each line shall be composed of the following four <tab>-separated
fields. (Implementations may allow any combination of one or more
white-space characters other than <newline> to act as field
separators.)
offset An unsigned number (optionally preceded by a single '>'
character) specifying the offset, in bytes, of the
value in the file that is to be compared against the
value field of the line. If the file is shorter than
the specified offset, the test shall fail.
If the offset begins with the character '>', the test
contained in the line shall not be applied to the file
unless the test on the last line for which the offset
did not begin with a '>' was successful. By default,
the offset shall be interpreted as an unsigned decimal
number. With a leading 0x or 0X, the offset shall be
interpreted as a hexadecimal number; otherwise, with a
leading 0, the offset shall be interpreted as an octal
number.
type The type of the value in the file to be tested. The
type shall consist of the type specification characters
d, s, and u, specifying signed decimal, string, and
unsigned decimal, respectively.
The type string shall be interpreted as the bytes from
the file starting at the specified offset and including
the same number of bytes specified by the value field.
If insufficient bytes remain in the file past the
offset to match the value field, the test shall fail.
The type specification characters d and u can be
followed by an optional unsigned decimal integer that
specifies the number of bytes represented by the type.
The type specification characters d and u can be
followed by an optional C, S, I, or L, indicating that
the value is of type char, short, int, or long,
respectively.
The default number of bytes represented by the type
specifiers d, f, and u shall correspond to their
respective C-language types as follows. If the system
claims conformance to the C-Language Development
Utilities option, those specifiers shall correspond to
the default sizes used in the c99 utility. Otherwise,
the default sizes shall be implementation-defined.
For the type specifier characters d and u, the default
number of bytes shall correspond to the size of a basic
integer type of the implementation. For these specifier
characters, the implementation shall support values of
the optional number of bytes to be converted
corresponding to the number of bytes in the C-language
types char, short, int, or long. These numbers can
also be specified by an application as the characters
C, S, I, and L, respectively. The byte order used when
interpreting numeric values is implementation-defined,
but shall correspond to the order in which a constant
of the corresponding type is stored in memory on the
system.
All type specifiers, except for s, can be followed by a
mask specifier of the form &number. The mask value
shall be AND'ed with the value of the input file before
the comparison with the value field of the line is
made. By default, the mask shall be interpreted as an
unsigned decimal number. With a leading 0x or 0X, the
mask shall be interpreted as an unsigned hexadecimal
number; otherwise, with a leading 0, the mask shall be
interpreted as an unsigned octal number.
The strings byte, short, long, and string shall also be
supported as type fields, being interpreted as dC, dS,
dL, and s, respectively.
value The value to be compared with the value from the file.
If the specifier from the type field is s or string,
then interpret the value as a string. Otherwise,
interpret it as a number. If the value is a string,
then the test shall succeed only when a string value
exactly matches the bytes from the file.
If the value is a string, it can contain the following
sequences:
\character The <backslash>-escape sequences as
specified in the Base Definitions volume of
POSIX.1‐2017, Table 5-1, Escape Sequences
and Associated Actions ('\\', '\a', '\b',
'\f', '\n', '\r', '\t', '\v'). In
addition, the escape sequence '\ ' (the
<backslash> character followed by a <space>
character) shall be recognized to represent
a <space> character. The results of using
any other character, other than an octal
digit, following the <backslash> are
unspecified.
\octal Octal sequences that can be used to
represent characters with specific coded
values. An octal sequence shall consist of
a <backslash> followed by the longest
sequence of one, two, or three octal-digit
characters (01234567).
By default, any value that is not a string shall be
interpreted as a signed decimal number. Any such value,
with a leading 0x or 0X, shall be interpreted as an
unsigned hexadecimal number; otherwise, with a leading
zero, the value shall be interpreted as an unsigned
octal number.
If the value is not a string, it can be preceded by a
character indicating the comparison to be performed.
Permissible characters and the comparisons they specify
are as follows:
= The test shall succeed if the value from the file
equals the value field.
< The test shall succeed if the value from the file
is less than the value field.
> The test shall succeed if the value from the file
is greater than the value field.
& The test shall succeed if all of the set bits in
the value field are set in the value from the
file.
^ The test shall succeed if at least one of the set
bits in the value field is not set in the value
from the file.
x The test shall succeed if the file is large
enough to contain a value of the type specified
starting at the offset specified.
message The message to be printed if the test succeeds. The
message shall be interpreted using the notation for the
printf formatting specification; see printf. If the
value field was a string, then the value from the file
shall be the argument for the printf formatting
specification; otherwise, the value from the file shall
be the argument.
