PX(1) General Commands Manual PX(1)NAME
px - Pascal interpreter
px [ obj [ argument ... ] ]
Px interprets the abstract machine code generated by pi. The first argument is the file to be interpreted, and defaults to obj; remaining
arguments are available to the Pascal program using the built-ins argv and argc. Px is also invoked by pix when running `load and go'.
If the program terminates abnormally an error message and a control flow backtrace are printed. The number of statements executed and
total execution time are printed after normal termination. The p option of pi suppresses all of this except the message indicating the
cause of abnormal termination.
obj default object file
pmon.out profile data file
Berkeley Pascal User's Manual
Most run-time error messages are self-explanatory. Some of the more unusual ones are:
Reference to an inactive file
A file other than input or output was used before a call to reset or rewrite.
Statement count limit exceeded
The limit of 500,000 executed statements (which prevents excessive looping or recursion) has been exceeded.
Bad data found on integer read
Bad data found on real read
Usually, non-numeric input was found for a number. For reals, Pascal requires digits before and after the decimal point so that num-
bers like `.1' or `21.' evoke the second diagnostic.
panic: Some message
Indicates a internal inconsistency detected in px probably due to a Pascal system bug. Charles B. Haley, William N. Joy, and Ken
Calls to the procedures dispose and linelimit are ignored.
Post-mortem traceback is not limited; infinite recursion leads to almost infinite traceback.
Because interrupts sometimes find the system in the middle of a procedure or function entry or exit, the error backtrace on an interrupt is
occasionally meaningless. The current line is, however, always correct; only the call backtrace and the name of the current routine may be
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PDX(1) General Commands Manual PDX(1)NAME
pdx - pascal debugger
pdx [-r] [objfile]
Pdx is a tool for source level debugging and execution of Pascal programs. 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 to create it. These files are available for perusal while using the
If the file ``.pdxinit'' exists in the current directory, then the debugger commands in it are executed.
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 speci-
fied, 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 current 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 func-
tion 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
If the argument is a variable then the name and value of the variable 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
Condition is a Pascal boolean expression and is evaluated prior to printing the tracing information; if it is false then the infor-
mation is not printed.
There is no restriction on the amount of information that can be traced.
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 function 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
current 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 function.
help Print out a synopsis of pdx commands.
gripe Invokes a mail program to send a message to the person in charge of pdx.
where 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 number 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 procedure or function and k is small.
Change the current source file name to filename. If none is specified 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
editor 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 environment 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 addresses.
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).
obj Pascal object file
.pdxinit Pdx initialization file
SEE ALSO pi(1), px(1)
An Introduction to Pdx
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-like history capability would improve the situation.
4.2 Berkeley Distribution April 29, 1985 PDX(1)