xprop - property displayer for X
xprop [-help] [-grammar] [-id id] [-root] [-name name]
[-frame] [-font font] [-display display] [-len n]
[-notype] [-fs file] [-remove property-name] [-spy] [-f
atom format[dformat]] * [format[dformat]atom] *
The xprop utility is for displaying window and font properties
in an X server. One window or font is selected
using the command line arguments or possibly in the case
of a window, by clicking on the desired window. A list of
properties is then given, possibly with formatting information.
Print out a summary of command line options. Print out a
detailed grammar for all command line options. This argument
allows the user to select window id on the command
line rather than using the pointer to select the target
window. This is very useful in debugging X applications
where the target window is not mapped to the screen or
where the use of the pointer might be impossible or interfere
with the application. This argument allows the user
to specify that the window named name is the target window
on the command line rather than using the pointer to
select the target window. This argument allows the user
to specify that the properties of font font should be displayed.
This argument specifies that X's root window is
the target window. This is useful in situations where the
root window is completely obscured. This argument allows
you to specify the server to connect to; see X(1X). Specifies
that at most n bytes of any property should be read
or displayed. Specifies that the type of each property
should not be displayed. Specifies that file file should
be used as a source of more formats for properties. Specifies
that when selecting a window by hand (that is, if
none of -name, -root, or -id are given), look at the window
manager frame (if any) instead of looking for the
client window. Specifies the name of a property to be
removed from the indicated window. Examine window properties
forever, looking for property change events. Specifies
that the format for name should be format and that
the dformat for name should be dformat. If dformat is
missing, " = $0+\n" is assumed.
For each of these properties, its value on the selected
window or font is printed using the supplied formatting
information if any. If no formatting information is supplied,
internal defaults are used. If a property is not
defined on the selected window or font, "not defined" is
printed as the value for that property. If no property
list is given, all the properties possessed by the
selected window or font are printed.
A window may be selected in one of four ways. First, if
the desired window is the root window, the -root argument
may be used. If the desired window is not the root
window, it may be selected in two ways on the command
line, either by id number such as might be obtained from
xwininfo, or by name if the window possesses a name. The
-id argument selects a window by id number in either decimal
or hex (must start with 0x) while the -name argument
selects a window by name.
The last way to select a window does not involve the command
line at all. If none of -font, -id, -name, and -root
are specified, a crosshairs cursor is displayed and the
user is allowed to choose any visible window by pressing
any pointer button in the desired window. If it is
desired to display properties of a font as opposed to a
window, the -font argument must be used.
Other than the above four arguments and the -help argument
for obtaining help, and the -grammar argument for listing
the full grammar for the command line, all the other command
line arguments are used in specifying both the format
of the properties to be displayed and how to display them.
The -len n argument specifies that at most n bytes of any
given property will be read and displayed. This is useful
for example when displaying the cut buffer on the root
window which could run to several pages if displayed in
full.
Normally each property name is displayed by printing first
the property name then its type (if it has one) in parentheses
followed by its value. The -notype argument specifies
that property types should not be displayed. The -fs
argument is used to specify a file containing a list of
formats for properties while the -f argument is used to
specify the format for one property.
The formatting information for a property actually consists
of two parts, a format and a dformat. The format
specifies the actual formatting of the property (that is,
is it made up of words, bytes, or longs?, and so forth.)
while the dformat specifies how the property should be
displayed.
The following paragraphs describe how to construct formats
and dformats. However, for the vast majority of users and
uses, this should not be necessary as the built in
defaults contain the formats and dformats necessary to
display all the standard properties. It should only be
necessary to specify formats and dformats if a new property
is being dealt with or the user dislikes the standard
display format. New users especially are encouraged to
skip this part.
A format consists of one of 0, 8, 16, or 32 followed by a
sequence of one or more format characters. The 0, 8, 16,
or 32 specifies how many bits per field there are in the
property. Zero is a special case meaning use the field
size information associated with the property itself.
(This is only needed for special cases like type INTEGER
which is actually three different types depending on the
size of the fields of the property)
A value of 8 means that the property is a sequence of
bytes while a value of 16 would mean that the property is
a sequence of words. The difference between these two
lies in the fact that the sequence of words will be byte
swapped while the sequence of bytes will not be when read
by a machine of the opposite byte order of the machine
that originally wrote the property. For more information
on how properties are formatted and stored, consult the
Xlib manual.
Once the size of the fields has been specified, it is necessary
to specify the type of each field (that is, is it
an integer, a string, an atom, or what?) This is done
using one format character per field. If there are more
fields in the property than format characters supplied,
the last character will be repeated as many times as necessary
for the extra fields. The format characters and
their meaning are as follows: The field holds an atom number.
A field of this type should be of size 32. The
field is an boolean. A 0 means false while anything else
means true. The field is an unsigned number, a cardinal.
The field is a signed integer. The field is a set of bit
flags, 1 meaning on. This field and the next ones until
either a 0 or the end of the property represent a sequence
of bytes. This format character is only usable with a
field size of 8 and is most often used to represent a
string. The field is a hex number (like 'c' but displayed
in hex - most useful for displaying window ids and the
like)
An example format is 32ica which is the format for a property
of three fields of 32 bits each, the first holding a
signed integer, the second an unsigned integer, and the
third an atom.
The format of a dformat unlike that of a format is not so
rigid. The only limitations on a dformat is that one may
not start with a letter or a dash. This is so that it can
be distinguished from a property name or an argument. A
dformat is a text string containing special characters
instructing that various fields be printed at various
points in a manner similar to the formatting string used
by printf. For example, the dformat " is ( $0, $1 \)\n"
would render the POINT 3, -4 which has a format of 32ii as
" is ( 3, -4 )\n".
Any character other than a $, ?, \, or a ( in a dformat
prints as itself. To print out one of $, ?, \, or ( precede
it by a \. For example, to print out a $, use \$.
Several special backslash sequences are provided as shortcuts.
\n will cause a newline to be displayed while \t
will cause a tab to be displayed. \o where o is an octal
number will display character number o.
A $ followed by a number n causes field number n to be
displayed. The format of the displayed field depends on
the formatting character used to describe it in the corresponding
format. I.e., if a cardinal is described by 'c'
it will print in decimal while if it is described by a 'x'
it is displayed in hex.
If the field is not present in the property (this is possible
with some properties), <field not available> is displayed
instead. $n+ will display field number n then a
comma then field number n+1 then another comma then ...
until the last field defined. If field n is not defined,
nothing is displayed. This is useful for a property that
is a list of values.
A ? is used to start a conditional expression, a kind of
if-then statement. ?exp(text) will display text if and
only if exp evaluates to non-zero. This is useful for two
things. First, it allows fields to be displayed if and
only if a flag is set. And second, it allows a value such
as a state number to be displayed as a name rather than as
just a number. The syntax of exp is as follows:
exp::= term | term=exp | !exp
term::= n | $n | mn
The ! operator is a logical "not", changing 0 to 1 and any
non-zero value to 0. = is an equality operator. Note that
internally all expressions are evaluated as 32 bit numbers
so -1 is not equal to 65535. = returns 1 if the two values
are equal and 0 if not. n represents the constant
value n while $n represents the value of field number n.
mn is 1 if flag number n in the first field having format
character 'm' in the corresponding format is 1, 0 otherwise.
Examples: ?m3(count: $3\n) displays field 3 with a label
of count if and only if flag number 3 (count starts at 0!)
is on. ?$2=0(True)?!$2=0(False) displays the inverted
value of field 2 as a boolean.
In order to display a property, xprop needs both a format
and a dformat. Before xprop uses its default values of a
format of 32x and a dformat of " = { $0+ }\n", it searches
several places in an attempt to find more specific formats.
First, a search is made using the name of the property.
If this fails, a search is made using the type of
the property. This allows type STRING to be defined with
one set of formats while allowing property WM_NAME which
is of type STRING to be defined with a different format.
In this way, the display formats for a given type can be
overridden for specific properties.
The locations searched are in order: the format if any
specified with the property name (as in 8x WM_NAME), the
formats defined by -f options in last to first order, the
contents of the file specified by the -fs option if any,
the contents of the file specified by the environmental
variable XPROPFORMATS if any, and finally xprop's built in
file of formats.
The format of the files referred to by the -fs argument
and the XPROPFORMATS variable is one or more lines of the
following form:
name format [dformat]
Where name is either the name of a property or the name of
a type, format is the format to be used with name and
dformat is the dformat to be used with name. If dformat
is not present, " = $0+\n" is assumed.
To display the name of the root window: xprop -root
WM_NAME
To display the window manager hints for the clock: xprop
-name xclock WM_HINTS
To display the start of the cut buffer: xprop -root -len
100 CUT_BUFFER0
To display the point size of the fixed font: xprop -font
fixed POINT_SIZE
To display all the properties of window # 0x200007: xprop
-id 0x200007
To get default display. Specifies the name of a file from
which additional formats are to be obtained.
X(1X), xwininfo(1X)
Mark Lillibridge, MIT Project Athena
xprop(1X)
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