bash storing the output of set -x to log file

Question

I have a simple download script and I use set -x which works great; I can see each step it performs, and I can identify errors in the script or in the download:

#!/bin/bash
set -x
#short_date=$(/bin/date +%m%d%y)
short_date=$(/bin/date -d "8 day ago" +%m%d%y)
#long_date=$(/bin/date +%Y%m%d)
long_date=$(/bin/date -d "8 day ago" +%Y%m%d)
scp -v -P 1332 -i /home/casper/.ssh/id_rsa_BANK [email protected]:/home/friendly/transfer/out/EXCHANGE_$short_date.csv /local/casper3/dailymetrics/BANK_$long_date.csv

I would like to automate this job. Is there a way I could save the set -x output to a log file? Maybe to one log file - or a different log file for each day. I don't know what would work best.

Below is sample set -x output from the above script.

++ /bin/date +%m%d%y
+ short_date=102814
++ /bin/date +%Y%m%d
+ long_date=20141028
+ scp -v -P 1332 -i /home/casper/.ssh/id_rsa_BANK [email protected]:/home/friendly/transfer/out/EXCHANGE_102814.csv /local/casper3/dailymetrics/BANK_20141028.csv
Executing: program /usr/bin/ssh host 192.168.1.10, user friendly, command scp -v -f /home/friendly/transfer/out/EXCHANGE_102814.csv
OpenSSH_5.3p1, OpenSSL 1.0.0-fips 29 Mar 2010
debug1: Reading configuration data /home/casper/.ssh/config
debug1: Reading configuration data /etc/ssh/ssh_config
debug1: Applying options for *
debug1: Connecting to 192.168.1.10 [192.168.1.10] port 7777.
debug1: Connection established.

Answer 1

Assuming bash 4, BASH_XTRACEFD can be set to override the file descriptor (by default 2, stderr) to which set -x output is written:

short_date=$(/bin/date +%m%d%y)
exec {BASH_XTRACEFD}>>"$short_date".log
set -x

If running bash 4.0 rather than 4.1 or newer, you have BASH_XTRACEFD but not automatic file descriptor allocation, meaning you'll need to assign one yourself; in the below example, I'm picking file descriptor 100:

short_date=$(/bin/date +%m%d%y)
exec 100>>"$short_date".log
BASH_XTRACEFD=100
set -x

For older releases, your only choice is to redirect all of stderr, rather than only the xtrace stream:

short_date=$(/bin/date +%m%d%y)
exec 2>>"$short_date.log"
set -x