Shell Programming and Scripting

Hi,

I'm trying to use sdiff by parsing the output of another command instead of the filename:

Code:

sdiff <(echo test1) <(echo test2)

However, this seems to cause my terminal session to stop working.

If I use it with normal diff it works fine:

Code:

~$ diff <(echo test1) <(echo test2)
1c1
< test1
---
> test2

Is there a way to use sdiff like I use diff in this example?

Thanks

If you check out sdiff using strace/truss/tusc, you can see where it goes wrong. This tool is very educational, turn on all the local options, and learn! Probably, it does seeks and so gets upset at the pipes. Try it with temp files.

Thanks for the reply DGPickett,

Unfortunately I can't use strace on this machine (unable to open /dev/log) and truss gives me a bunch of:

Code:

write(1, "\n", 1)                               = 1
read(3, 0x08066234, 5120)                       = 0

Nevertheless, it's probably a very useful tool which I can and will use for other problems

Hi.

For this system:

Code:

OS, ker|rel, machine: Linux, 2.6.26-2-amd64, x86_64
Distribution        : Debian GNU/Linux 5.0.8 (lenny) 
bash GNU bash 3.2.39
sdiff (GNU diffutils) 2.8.1

I get this:

Code:

sdiff <(echo test1) <(echo test2)sdiff <(echo test1) <(echo test2)
test1							      |	test2

The strace with first line:

Code:

strace sdiff <(echo test1) <(echo test2)
execve("/usr/bin/sdiff", ["sdiff", "/dev/fd/63", "/dev/fd/62"], [/* 48 vars */]) = 0

Best wishes ... cheers, drl

Yes, that is what strace/tusc/truss do, they give you all the system calls and their results, and sometimes other library calls can be selected. On Solaris, -u'*' says show every user lib call, so you can see everything not a macro: fgets, printf, strchr, etc. And you do not need source code, or to set anythig before it starts running, to peek at what is going on, you can attach with -p PID. In some cases, I need to see the launch, so I call it like this:

Code:

$ ( sleep 2
   test-comand-line
 )& truss ... -o /tmp/xxx.tr -p $!

To just take a peek, run the truss output (defaults to stderr) into a head command and just sample N lines. When truss cannot write, it detaches and exits. Thigs do run slower with truss attached, as it instructs the kernel to stall the target while it tells truss what it is up to.

This is a wonderfully educational and stupendously powerful tool. Play with it.

My tusc of hpux 11.00 trace says it opens the pipes and then passes their names to diff -b, which also opens them. Named pipes opened once for write do not open twice for read, they hang awaiting the second open for write. The shell named pipes /dev/fd/### are, if anything, even less interested in a second open() of any sort, and that fd number may be occupied by another file after the fork and exec and all such nonsense. So, not pipe friendly, and the sad thing is that sdiff does a stat of the pipe name before opening it, but ignores that it is a pipe. Then diff -b does seeks and ignores the errors.