> is this idea confusing ?
The simple
> file 2>&1
to make sure that err output is included in the file
and
cmd1 2>&1 | cmd2
to make sure that err output is included in the input to cmd2,
are used a lot.
Nothing wrong with using more than the usual 0,1,2 file descriptors and it can be useful.
However, it is an advanced concept, and, for the casual peruser, it can take a while to figure out what's going on.
OTOH, well documenting the script at the beginning takes care of that issue.
In a fairly complex script, you might have several different log files to which output will be sent at various times by various commands.
You could accomodate that in at least two ways
1) set up multiple FDs
exec 3>/tmp/lg1
exec 4>/tmp/lg2
exec 5>/tmp/lg2e
and some commands might use use
acmd >&3 2>&1
while others might use
bcmd >&4 2>&5
This method has the quirk (or advantage) of automatically appending output since the FDs are opened thoughout the script's process (unless closed, of course).
You can see this with this scriptlet:
## (
>/tmp/l1
exec 3>/tmp/l1
echo gkgkgkg >&3 # to FD 3 with no >>
cat /tmp/l1
echo --
echo hhhhhkg >&3 # to FD 3 with no >>
cat /tmp/l1
echo --
ll /tmp/l2 /tmp/xxl1 >&3 2>&1
cat /tmp/l1
)
2) but, in most cases, you could also just set up some variables
LOG1=/tmp/lg1
LOG2=/tmp/lg2
LOG2e=/tmp/lg2e
and manually append them:
> $LOG1 ; > $LOG2 ; > $LOG2e # init them
acmd >> $LOG1 2>&1
bcmd >> $LOG2 2>>$LOG2e
With "disadvantage" of requiring '>>',
but with the advantage of being more readable and maybe self-documenting.
Another scriptlet:
## (
LOG1=/tmp/lg1
LOG2=/tmp/lg2
LOG2e=/tmp/lg2e
> $LOG1 ; > $LOG2 ; > $LOG2e # init them
ll /tmp/l2 /tmp/xxl1 >> $LOG1 2>&1
vgdisplay >> $LOG2 2>>$LOG2e
echo ------------LOG1--------------------------
cat $LOG1
echo ------------LOG2--------------------------
tail -5 $LOG2
echo ------------LOG2e-------------------------
cat $LOG2e
echo ===========
echo ===========
ll /tmp/l3 /tmp/aal1 >> $LOG1 2>&1
ll /tmp/l3 /tmp/aal1 >> $LOG2 2>>$LOG2e
echo ------------LOG1--------------------------
cat $LOG1
echo ------------LOG2--------------------------
tail -5 $LOG2
echo ------------LOG2e-------------------------
cat $LOG2e
)
I like that you used it -- shows that you are unafraid.
And, it's opened up another concept for discussion!
bv
"The lyf so short, the craft so long to lerne." - Chaucer
