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Bash: Complete wrapper for command line programs [on hold]

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0

1

Is it possible (and if, how) to write a complete wrapper for a generic command line program in bash.

With complete, I mean that it should behave with respect to the digestion of the different allowed forms of inputs and its outputs like the wrapped, unspecified, command line program itself.

In particular, it should forward all arguments specified at the command line and, if present, any input sent through stdin via a pipe.

I am not primarily thinking of input through signals (aka kill -s USR1 pid), albeit that would be interesting as well. Also, I may be overlooking other possible forms of communication that may be relevant, but these are not a priority either.

With respect to command line output and interactive input (read) it should also show the same behavior as the wrapped program itself (but that seems to be largely the case 'by default' when invoking a command line program from within a bash script in the straight-forward way).

The background is that I have a program interacting with the input in some unknown way. Trying to replace it with a wrapper, I found that the interaction with its caller does not work anymore. The purpose of the wrapper is to modify one of the input arguments.

You may assume that the caller invokes the program (or the wrapper) via a shell or with exec or a similar system call. That is, the caller does not in some way analyse the content of the original program to determine its behavior.

In summary, the required behavior of the wrapper is

• Forward stdin to the wrapped command




• Forward command line arguments to the wrapped command




• Forward stdout and stderr of the wrapped command to the caller




• Forward interactive input to the wrapped command if it reads

Since the last two should be 'default', and the second one pretty obvious ("$@") it seems that the challenge is mostly to forward stdin properly, but it would also good to know what else should be considered.

bash shell-script command-line

share|improve this question

edited yesterday

highsciguy

asked yesterday

highsciguyhighsciguy

99231121

put on hold as unclear what you're asking by Rui F Ribeiro, X Tian, roaima, G-Man, jimmij 20 hours ago

Please clarify your specific problem or add additional details to highlight exactly what you need. As it's currently written, it’s hard to tell exactly what you're asking. See the How to Ask page for help clarifying this question. If this question can be reworded to fit the rules in the help center, please edit the question.

• 
  
  
  

  
  1
  

  
  
  
  
  
  

  
  
  I'm really sorry, but I haven't got a clue what you're actually asking. Maybe some code examples might help.
  
  – roaima
  yesterday
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  I want a wrapper implemented in bash. A script that sits in-between the caller and the program that the caller normally calls. The program and the caller are fixed (I cannot modify them) and the caller expects to interact with the program in a certain way. The wrapper should imitate that interface as good as possible such that it is transparent to the caller.
  
  – highsciguy
  yesterday
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  It can be possible as long as the wrapped program just reads from stdin and writes to stdout/stderr. I can elaborate a full answer for that. Signals handling can be possible too. But if instead the wrapped program expects its stdin/stdout to be a tty, (which is something more than mere interactivity), then I’m afraid you can’t emulate that in bash. Also, wrt other possible communication channels, is it possibly not the case that the caller program expects the called program to create eg sockets or some kind of IPC ?
  
  – LL3
  yesterday
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  I think you can ignore the possibility of a tty (its a relevant mention that this possibility exists). I didn't have time to look at the link posted by @JShorthouse below. Maybe its relevant.
  
  – highsciguy
  yesterday
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  @highsciguy Yes it is relevant. If expect is not appropriate for your case, then have a look also at my own answer in @JShorthouse 's question of two days ago. My answer there may hint you about a possible bash implementation of what you need. That was tailored to his case but can be adjusted for your case.
  
  – LL3
  yesterday
  
  

  
  
  
  

 | 
show 1 more comment

0

1

Is it possible (and if, how) to write a complete wrapper for a generic command line program in bash.

With complete, I mean that it should behave with respect to the digestion of the different allowed forms of inputs and its outputs like the wrapped, unspecified, command line program itself.

In particular, it should forward all arguments specified at the command line and, if present, any input sent through stdin via a pipe.

I am not primarily thinking of input through signals (aka kill -s USR1 pid), albeit that would be interesting as well. Also, I may be overlooking other possible forms of communication that may be relevant, but these are not a priority either.

With respect to command line output and interactive input (read) it should also show the same behavior as the wrapped program itself (but that seems to be largely the case 'by default' when invoking a command line program from within a bash script in the straight-forward way).

The background is that I have a program interacting with the input in some unknown way. Trying to replace it with a wrapper, I found that the interaction with its caller does not work anymore. The purpose of the wrapper is to modify one of the input arguments.

You may assume that the caller invokes the program (or the wrapper) via a shell or with exec or a similar system call. That is, the caller does not in some way analyse the content of the original program to determine its behavior.

In summary, the required behavior of the wrapper is

• Forward stdin to the wrapped command




• Forward command line arguments to the wrapped command




• Forward stdout and stderr of the wrapped command to the caller




• Forward interactive input to the wrapped command if it reads

Since the last two should be 'default', and the second one pretty obvious ("$@") it seems that the challenge is mostly to forward stdin properly, but it would also good to know what else should be considered.

bash shell-script command-line

share|improve this question

edited yesterday

highsciguy

asked yesterday

highsciguyhighsciguy

99231121

put on hold as unclear what you're asking by Rui F Ribeiro, X Tian, roaima, G-Man, jimmij 20 hours ago

Please clarify your specific problem or add additional details to highlight exactly what you need. As it's currently written, it’s hard to tell exactly what you're asking. See the How to Ask page for help clarifying this question. If this question can be reworded to fit the rules in the help center, please edit the question.

• 
  
  
  

  
  1
  

  
  
  
  
  
  

  
  
  I'm really sorry, but I haven't got a clue what you're actually asking. Maybe some code examples might help.
  
  – roaima
  yesterday
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  I want a wrapper implemented in bash. A script that sits in-between the caller and the program that the caller normally calls. The program and the caller are fixed (I cannot modify them) and the caller expects to interact with the program in a certain way. The wrapper should imitate that interface as good as possible such that it is transparent to the caller.
  
  – highsciguy
  yesterday
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  It can be possible as long as the wrapped program just reads from stdin and writes to stdout/stderr. I can elaborate a full answer for that. Signals handling can be possible too. But if instead the wrapped program expects its stdin/stdout to be a tty, (which is something more than mere interactivity), then I’m afraid you can’t emulate that in bash. Also, wrt other possible communication channels, is it possibly not the case that the caller program expects the called program to create eg sockets or some kind of IPC ?
  
  – LL3
  yesterday
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  I think you can ignore the possibility of a tty (its a relevant mention that this possibility exists). I didn't have time to look at the link posted by @JShorthouse below. Maybe its relevant.
  
  – highsciguy
  yesterday
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  @highsciguy Yes it is relevant. If expect is not appropriate for your case, then have a look also at my own answer in @JShorthouse 's question of two days ago. My answer there may hint you about a possible bash implementation of what you need. That was tailored to his case but can be adjusted for your case.
  
  – LL3
  yesterday
  
  

  
  
  
  

 | 
show 1 more comment

Is it possible (and if, how) to write a complete wrapper for a generic command line program in bash.

With complete, I mean that it should behave with respect to the digestion of the different allowed forms of inputs and its outputs like the wrapped, unspecified, command line program itself.

In particular, it should forward all arguments specified at the command line and, if present, any input sent through stdin via a pipe.

I am not primarily thinking of input through signals (aka kill -s USR1 pid), albeit that would be interesting as well. Also, I may be overlooking other possible forms of communication that may be relevant, but these are not a priority either.

With respect to command line output and interactive input (read) it should also show the same behavior as the wrapped program itself (but that seems to be largely the case 'by default' when invoking a command line program from within a bash script in the straight-forward way).

The background is that I have a program interacting with the input in some unknown way. Trying to replace it with a wrapper, I found that the interaction with its caller does not work anymore. The purpose of the wrapper is to modify one of the input arguments.

You may assume that the caller invokes the program (or the wrapper) via a shell or with exec or a similar system call. That is, the caller does not in some way analyse the content of the original program to determine its behavior.

In summary, the required behavior of the wrapper is

• Forward stdin to the wrapped command




• Forward command line arguments to the wrapped command




• Forward stdout and stderr of the wrapped command to the caller




• Forward interactive input to the wrapped command if it reads

Since the last two should be 'default', and the second one pretty obvious ("$@") it seems that the challenge is mostly to forward stdin properly, but it would also good to know what else should be considered.

bash shell-script command-line

share|improve this question

edited yesterday

highsciguy

asked yesterday

highsciguyhighsciguy

99231121

share|improve this question

edited yesterday

highsciguy

asked yesterday

highsciguyhighsciguy

99231121

share|improve this question

edited yesterday

highsciguy

asked yesterday

highsciguyhighsciguy

99231121

asked yesterday

highsciguyhighsciguy

99231121

asked yesterday

highsciguyhighsciguy

99231121

1 Answer
1

active

oldest

votes

0

I think you're looking for expect.

Related question: Shell Script for logging into a ssh server

share|improve this answer

answered yesterday

JShorthouseJShorthouse

50728

New contributor

JShorthouse is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.

• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  Thanks, I am aware of expect, but, unless it has uses other than the one I am thinking of, it is not what I am looking for. My present understanding is that its prime purpose is to interact with a programs output in an automated fashion. My wrapper should have the default behavior of a bash script regarding the forwarding of outputs (stdout, stderr) and also interactive input. I am not interested in modifying or parsing these.
  
  – highsciguy
  yesterday
  
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  Ah ok, does this question sound similar to what you are trying to achieve? If I'm understanding you correctly then I was trying to solve a very similar problem a couple of days ago, and it can be done with expect.
  
  – JShorthouse
  yesterday
  
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  This answer sounds more a comment
  
  – Rui F Ribeiro
  yesterday
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  We try to avoid link-only answers here. Would you be able to summarise the important bits from the page that you link to in such a way that your answer becomes self contained?
  
  – Kusalananda♦
  yesterday
  
  

  
  
  
  

add a comment | 

0

I think you're looking for expect.

Related question: Shell Script for logging into a ssh server

share|improve this answer

answered yesterday

JShorthouseJShorthouse

50728

New contributor

JShorthouse is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.

• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  Thanks, I am aware of expect, but, unless it has uses other than the one I am thinking of, it is not what I am looking for. My present understanding is that its prime purpose is to interact with a programs output in an automated fashion. My wrapper should have the default behavior of a bash script regarding the forwarding of outputs (stdout, stderr) and also interactive input. I am not interested in modifying or parsing these.
  
  – highsciguy
  yesterday
  
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  Ah ok, does this question sound similar to what you are trying to achieve? If I'm understanding you correctly then I was trying to solve a very similar problem a couple of days ago, and it can be done with expect.
  
  – JShorthouse
  yesterday
  
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  This answer sounds more a comment
  
  – Rui F Ribeiro
  yesterday
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  We try to avoid link-only answers here. Would you be able to summarise the important bits from the page that you link to in such a way that your answer becomes self contained?
  
  – Kusalananda♦
  yesterday
  
  

  
  
  
  

add a comment | 

0

I think you're looking for expect.

Related question: Shell Script for logging into a ssh server

share|improve this answer

answered yesterday

JShorthouseJShorthouse

50728

New contributor

JShorthouse is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.

• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  Thanks, I am aware of expect, but, unless it has uses other than the one I am thinking of, it is not what I am looking for. My present understanding is that its prime purpose is to interact with a programs output in an automated fashion. My wrapper should have the default behavior of a bash script regarding the forwarding of outputs (stdout, stderr) and also interactive input. I am not interested in modifying or parsing these.
  
  – highsciguy
  yesterday
  
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  Ah ok, does this question sound similar to what you are trying to achieve? If I'm understanding you correctly then I was trying to solve a very similar problem a couple of days ago, and it can be done with expect.
  
  – JShorthouse
  yesterday
  
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  This answer sounds more a comment
  
  – Rui F Ribeiro
  yesterday
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  We try to avoid link-only answers here. Would you be able to summarise the important bits from the page that you link to in such a way that your answer becomes self contained?
  
  – Kusalananda♦
  yesterday
  
  

  
  
  
  

add a comment | 

I think you're looking for expect.

Related question: Shell Script for logging into a ssh server

share|improve this answer

answered yesterday

JShorthouseJShorthouse

50728

New contributor

JShorthouse is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.

share|improve this answer

answered yesterday

JShorthouseJShorthouse

50728

New contributor

JShorthouse is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.

answered yesterday

JShorthouseJShorthouse

50728

New contributor

JShorthouse is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.

answered yesterday

JShorthouseJShorthouse

50728