CODEWITHSUNDEEP
linuxbashshellsh
MacUsers
MacUsers

Reputation: 2229

How to prepend timestamp to the STDERR and redirect to a file

I'm redirecting only the STDERR to a file (which is more or less working) but I also want to add/prepend a time-stamp for each redirection. I don't want the time in every line, just at the beginning of the block. I tried this: 

UKMAC08:~ san$ ( date 1>&2; df -jj ) 2>&1 1>/dev/null  2>testErr.log; cat testErr.log 
Fri  1 Aug 2014 10:50:00 BST
df: illegal option -- j
usage: df [-b | -H | -h | -k | -m | -g | -P] [-ailn] [-T type] [-t] [filesystem ...]

Which is doing what I want to do for an unsuccessful run but also putting the time-stamp when it's a success:

UKMAC08:~ san$ ( date 1>&2; df -h ) 2>&1 1>/dev/null  2>testErr.log; cat testErr.log 
Fri  1 Aug 2014 10:50:07 BST

How can I avoid that. Best!

Upvotes: 3

Views: 1489

Answers (2)

twalberg
twalberg

Reputation: 62389

How about something like this:

date > stderr.log
command 2>> stderr.log

That seems the simplest way to me - simply pre-seed your output file with the date, then append the stderr output, instead of overwriting the file...

Upvotes: 0

konsolebox
konsolebox

Reputation: 75488

This can do:

OUT=$(df -h 2>&1 >/dev/null) || { date; echo "$OUT"; } >testErr.log

Test:

$ : > testErr.log; OUT=$(df -jj 2>&1 >/dev/null) || { date -u; echo "$OUT"; } >testErr.log; cat testErr.log
Fri Aug  1 12:10:29 UTC 2014
df: invalid option -- 'j'
Try 'df --help' for more information.
$ : > testErr.log; OUT=$(df -h 2>&1 >/dev/null) || { date -u; echo "$OUT"; } >testErr.log; cat testErr.log
(no output)

You can change >testErr.log to >>testErr.log to append.

And this can be more efficient:

OUT=$(exec df -h 2>&1 >/dev/null) || { date; echo "$OUT"; } >testErr.log

Upvotes: 2

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