Greg Wooledge wrote:
On Sat, Oct 17, 2015 at 05:43:15PM -0700, Linda Walsh wrote:
Chet Ramey wrote:
I think you're missing that process substitution is a word expansion
that is defined to expand to a filename.
-----
??? I've never seen a usage where it expands to a filename and
is treated as such.
A simple example:
diff -u <(sort file1) <(sort file2)
----
You claim <(sort file1) is a filename?
touch a
mv <(sort a) <(sort a)
mv: cannot move ‘/dev/fd/63’ to ‘/dev/fd/62’: Operation not permitted
The OS claims that <() generates a file descriptor -- not a filename.
"<()" is not the same, nor equivalent to a filename. It represents
a *file descriptor* that you can perform stream I/O on.
It's the same with 'FILENAME'a used with "read < FILENAME >FILENAME"
read < FILE > FILE
-bash: FILE: No such file or directory # no file is created by '>'
echo content >FILE
read mycontent < FILE >FILE
echo $mycontent # empty: file truncated before read
a=<(sort a); chmod +x "$a"
chmod: cannot access ‘/dev/fd/63’: No such file or directory
echo aaa > a
read var <(sort a) && echo "var=$var" >a
## the above hangs: if <(sort a), was a filename, read would
## have read 'aaa' ## from it, and returned immediately.
## Then the 'echo' command would have put 'var=aaa'
## in 'a': instead:
cat a
aaa
The above operations show that <() is not equivalent to a filename.
It only returns a 'path' to a *device* that doesn't have file semantics
and can only be opened for read... and even that doesn't
appear to work all the time.
I observe similar inconsistencies and confusion around
the use of 'dynamic vars' -- not really being global, not really
being local, but supposedly on some dynamic frame, "somewhere",
but not anywhere they've been declared or used.
