PDX(1) BSD General Commands Manual PDX(1)NAMEpdx — pascal debugger
SYNOPSISpdx [-r] [objfile]
Pdx is a tool for source level debugging and execution of Pascal pro‐
grams. The objfile is an object file produced by the Pascal translator
pi(1). If no objfile is specified, pdx looks for a file named ``obj'' in
the current directory. The object file contains a symbol table which
includes the name of the all the source files translated by pi(1) to cre‐
ate it. These files are available for perusal while using the debugger.
If the file “.pdxinit” exists in the current directory, then the debugger
commands in it are executed.
-r The -r option causes the objfile to be executed immediately; if it
terminates successfully pdx exits. Otherwise it reports the reason
for termination and offers the user the option of entering the
debugger or simply letting px continue with a traceback. If -r is
not specified, pdx just prompts and waits for a command.
The commands are:
run [args] [< filename] [> filename]
Start executing objfile, passing args as command line arguments; <
or > can be used to redirect input or output in the usual manner.
trace [in procedure/function] [if condition]
trace source-line-number [if condition]
trace procedure/function [in procedure/function] [if condition]
trace expression at source-line-number [if condition]
trace variable [in procedure/function] [if condition]
Have tracing information printed when the program is executed. A
number is associated with the command that is used to turn the
tracing off (see the delete command).
The first argument describes what is to be traced. If it is a
source-line-number, then the line is printed immediately prior to
being executed. Source line numbers in a file other than the cur‐
rent one must be preceded by the name of the file and a colon, e.g.
If the argument is a procedure or function name then every time it
is called, information is printed telling what routine called it,
from what source line it was called, and what parameters were
passed to it. In addition, its return is noted, and if it's a
function then the value it is returning is also printed.
If the argument is an expression with an at clause then the value
of the expression is printed whenever the identified source line is
If the argument is a variable then the name and value of the vari‐
able is printed whenever it changes. Execution is substantially
slower during this form of tracing.
If no argument is specified then all source lines are printed
before they are executed. Execution is substantially slower during
this form of tracing.
The clause “in procedure/function” restricts tracing information to
be printed only while executing inside the given procedure or func‐
Condition is a Pascal boolean expression and is evaluated prior to
printing the tracing information; if it is false then the informa‐
tion is not printed.
There is no restriction on the amount of information that can be
stop if condition
stop at source-line-number [if condition]
stop in procedure/function [if condition]
stop variable [if condition]
Stop execution when the given line is reached, procedure or func‐
tion called, variable changed, or condition true.
The trace or stop corresponding to the given number is removed.
The numbers associated with traces and stops are printed by the
status [> filename]
Print out the currently active trace and stop commands.
cont Continue execution from where it stopped. This can only be done
when the program was stopped by an interrupt or through use of the
step Execute one source line.
next Execute up to the next source line. The difference between this
and step is that if the line contains a call to a procedure or
function the step command will stop at the beginning of that block,
while the next command will not.
print expression [, expression ...]
Print out the values of the Pascal expressions. Variables declared
in an outer block but having the same identifier as one in the cur‐
rent block may be referenced as “block-name . variable”
Print the declaration of the given identifier.
Print the full qualification of the given identifer, i.e. the
outer blocks that the identifier is associated with.
assign variable expression
Assign the value of the expression to the variable.
Execute the object code associated with the named procedure or
help Print out a synopsis of pdx commands.
Invokes a mail program to send a message to the person in charge of
Print out a list of the active procedures and functions and the
respective source line where they are called.
Read pdx commands from the given filename. Especially useful when
the filename has been created by redirecting a status command from
an earlier debugging session.
dump [> filename]
Print the names and values of all active data.
list [source-line-number [, source-line-number]]
List the lines in the current source file from the first line num‐
ber to the second inclusive. As in the editor ``$'' can be used to
refer to the last line. If no lines are specified, the entire file
is listed. If the name of a procedure or function is given lines
n-k to n+k are listed where n is the first statement in the proce‐
dure or function and k is small.
Change the current source file name to filename. If none is speci‐
fied then the current source file name is printed.
Invoke an editor on filename or the current source file if none is
specified. If a procedure or function name is specified, the edi‐
tor is invoked on the file that contains it. Which editor is
invoked by default depends on the installation. The default can be
overridden by setting the environment variable EDITOR to the name
of the desired editor.
pi Recompile the program and read in the new symbol table information.
Pass the command line to the shell for execution. The SHELL envi‐
ronment variable determines which shell is used.
alias new-command-name old-command-name
This command makes pdx respond to new-command-name the way it used
to respond to old-command-name.
quit Exit pdx.
The following commands deal with the program at the px instruction level
rather than source level. They are not intended for general use.
tracei [address] [if cond]
tracei [variable] [at address] [if cond]
stopi [address] [if cond]
stopi [at] [address] [if cond]
Turn on tracing or set a stop using a px machine instruction
xi address [, address]
Print the instructions starting at the first address.
Instructions up to the second address are printed.
xd address [, address]
Print in octal the specified data location(s).
EDITOR The edit function uses the EDITOR environment variable to
see what editor to use.
SHELL The function sh checks the SHELL variable to see which
shell to execute.
obj Pascal object file
.pdxinit Pdx initialization file
SEE ALSOpi(1), px(1)
An Introduction to Pdx.
Pdx appeared in 4.2BSD.
Pdx does not understand sets, and provides no information about files.
The whatis command doesn't quite work for variant records.
Bad things will happen if a procedure invoked with the call command does
a non-local goto.
The commands step and next should be able to take a count that specifies
how many lines to execute.
There should be commands stepi and nexti that correspond to step and next
but work at the instruction level.
There should be a way to get an address associated with a line number,
procedure or function, and variable.
Most of the command names are too long.
The alias facility is quite weak.
A csh(1)-like history capability would improve the situation.
4.2 Berkeley Distribution June 6, 1993 4.2 Berkeley Distribution