multiple variables assignement (stdout/stderr outputs) Post: 302447966

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Top Forums UNIX for Dummies Questions & Answers multiple variables assignement (stdout/stderr outputs) Post 302447966 by agama on Tuesday 24th of August 2010 11:06:00 PM

08-25-2010

Registered User

Quote:

Originally Posted by anthalamus

I would like to assign the output of stdout to a variable and that of stderr to another one, and this without using temporary files/named pipes.

I agree with Corona688, cannot be done without pipes. However, you said 'named pipes' which technically are different beasts so I offer this "mess" for you to consider.

Code:

#!/usr/bin/env ksh 
(ls *.jpg bfoo | sed 's/^/STDOUT /') 2>&1 | awk ' 
        /STDOUT/ { 
                gsub( "STDOUT ", "" ); 
                o1 = o1 $0 "; "; 
                next;
        } 
        {
                o2 = o2 $0 "; ";
        } 
        END{ 
                printf( "%s~%s\n", o1, o2 ); 
        }' |  IFS="~" read  stdout stderr
echo "stdout=$stdout"
echo "stderr=$stderr"

It all can be crammed on one line; I've formatted it to be easier to read. It makes the assumption that the tilde (~) is never found in either the stdout or stderr stream. The records of each output stream are separated with semicolons, so if the output contains them, things will be difficult.

Running the script in my small test environment produced:

Code:

$ t20   
stdout=bar.jpg; foo.jpg; snapshot.jpg; 
stderr=ls: bfoo: not found;

I tested this in Kshell; I don't think it will work under bash as bash has issues executing a command and reading the output into variables. It will also be subject to the limits that Kshell might impose on variable value lengths or that awk might impose on string lengths. If you have a command that produces rather long output/error you could have problems.

Regardless, interesting brain twister.

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LEARN ABOUT DEBIAN

filter_create_fd

filter_create_fd(3)						   util/filter.h					       filter_create_fd(3)

NAME

       filter_create_fd  - Create a sub process and return the requested pipes

SYNOPSIS

       #include <util/filter.h>

       NEOERR *filter_create_fd(const char *cmd, int *fdin, int *fdout, int *fderr,
				pid_t *pid);

ARGUMENTS

       cmd -> the sub command to execute.  Will be executed with
       /bin/sh -c
       fdin -> pointer to return the stdin pipe, or NULL if you don't
       want the stdin pipe
       fdout -> pointer to return the stdout pipe, or NULL if you don't
       want the stdout pipe
       fderr -> pointer to return the stderr pipe, or NULL if you don't
       want the stderr pipe

DESCRIPTION

       filter_create_fd and filter_create_fp are what popen

       been:  a  mechanism  to	create sub processes and have pipes to all their input/output.	The concept was taken from mutt, though python has
       something similar with popen3/popen4.  You control which pipes the function returns by the fdin/fdout/fderr arguments.  A NULL value  means
       "don't  create a pipe", a pointer to an int will cause the pipes to be created and the value of the file descriptor stored in the int.  You
       will have to close(2) the file descriptors yourself.

RETURN VALUE

       fdin -> the stdin file descriptor of the sub process
       fdout -> the stdout file descriptor of the sub process
       fderr -> the stderr file descriptor of the sub process
       pid -> the pid of the sub process

SEE ALSO

       filter_wait(3), filter_create_fp(3), filter_create_fd

ClearSilver							   12 July 2007 					       filter_create_fd(3)

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