joining multiple PDFs into one

[Yanni Chiu]

On 15/11/11 12:37 PM, Russ wrote:
 > Everything is affected by the variables set by the shell when it is
 > started. When the shell allows clobbering, existing file data is
 > overwritten on cat something>  somefile, when it doesn't, existing
 > data is preserved.

First, did you try doing:

$ rm -f f f3
$ echo hello > f
$ cat f f f > f3

with noclobber set and not set, and see that it made no difference? Of 
course, if you skip the 'rm -f f f3' AND have noclobber set on, then any 
existing file f or f3 will not be changed, so the 'cat' command will 
then have no affect.

Second, try doing:

$ rm -f f f3
$ echo hello > f
$ cat f f f

What do you see on your terminal window? It should be:

$ rm -f f f3
$ echo hello > f
$ cat f f f
hello
hello
hello

If you redirect stdout to file 'f3' using '> f3', why should it be 
anything different from what appears on the terminal, whether or not 
noclobber is set (and f3 does not already exist).

Now back to the other alternative:

$ echo hello > f
$ cat f > f3
$ cat f >> f3
$ cat f >> f3

It is equivalent code, because the the first '> f3' clobbers f3 with the 
contents of f (assuming noclobber does not prevent the overwrite). The 
second and third '>> f3' will append a second and third copy of f. The 
'>>' is the shell's append operator.

I'm not sure how to explain it any more clearly. You really have to try 
the commands in a terminal, and see the results yourself.
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