CODEWITHSUNDEEP
http-redirectemacsgdbcommand-line-arguments
vinc456
vinc456

Reputation: 2880

How to load program reading stdin and taking parameters in gdb?

Question cribbed from here:

I have a program that takes input from stdin and also takes some parameters from command line. It looks like this:

cat input.txt > myprogram -path "/home/user/work"

I try to debug the code with gdb inside emacs, by M-x gdb, I try to load the program with the command:

gdb cat input.txt > myprogram -path "/home/user/work"

However, gdb does not like it.

Unfortunately I don't understand the solution and am not sure what to do beyond compiling with the -g option and running the command M-x gdb.

Upvotes: 123

Views: 99663

Answers (7)

user2226755
user2226755

Reputation: 13159

Getting inputs from char *argv[]

In bash:

$> ./myprogram -path "/home/user/work"

In gdb:

(gdb) run -path "/home/user/work"

Getting inputs from stdin

First way with cat :

In bash:

$> cat ./input.txt | ./program

In gdb:

(gdb) run < ./input.txt

Second way with a command :

In bash:

$> python -c 'print("input")' | ./myprogram

In gdb:

(gdb) run < <(python -c 'print("input")')

With the bash process substitution <(cmd) trick.

If there is several readline:

In gdb:

(gdb) run < <(python -c 'print("readline1")'; python -c 'print("readline2")')

Source: https://www.labri.fr/perso/fleury/posts/security/payload-injection.html

Upvotes: 0

Klapaucius Klapaucius
Klapaucius Klapaucius

Reputation: 689

I want to point to the technique with mkfifo as described here:

gdb - debugging with pipe

if you have a more complicated pipe than reading from just one file, such as:

cat jonesforth.f examples/defining-words.f - |./jonesforth

the mkfifo can be very convenient.

Upvotes: 0

EHM
EHM

Reputation: 959

This is eleven years later, and this question has an answer already, but for someone just like me in the future, I just wanted to add some thing.

After you run gdb your_program, if you just type run < file_containing_input, the program will just run till the end, and you might not catch the problem, so before you do run < file_containing_input do a break. Something like this

$ gdb your_program
gdb> break main
gdb> run < file_containing_input

Upvotes: 7

maxschlepzig
maxschlepzig

Reputation: 39027

There are several ways to do it:

$ gdb myprogram
(gdb) r -path /home/user/work < input.txt

or

$ gdb myprogram
(gdb) set args -path /home/user/work < input.txt
(gdb) r

or

$ gdb -ex 'set args -path /home/user/work < input.txt' myprogram
(gdb) r

where the gdb run command (r) uses by default the arguments as set previously with set args.

Upvotes: 35

vinc456
vinc456

Reputation: 2880

For completeness' sake upon starting a debugging session there is also the --args option. ie)

gdb gdbarg1 gdbarg2 --args yourprog arg1 arg2 -x arg3

Upvotes: 5

Zitrax
Zitrax

Reputation: 20246

And if you do not need to debug from the very beginning you can also attach to an already running process by using:

$ gdb myprogram xxx

where xxx is the process id. Then you do not need to tell gdb the starting arguments.

Upvotes: 1

Alnitak
Alnitak

Reputation: 339776

If you were doing it from a shell you'd do it like this:

% gdb myprogram
gdb> run params ... < input.txt

This seems to work within emacs too.

Upvotes: 158

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