Shell script timestamp variable

**fr33z0n3r** · February 28th, 2015

I'm no linux expert so I was hoping someone could help me on this shell script issue with a timestamp variable.

This is the line I have in use. It is a line to insert into my logfile for the shell script. I am noticing that the date does not update when I reuse the variable LOGENTRY. How can I get this variable to update the timestamp?

Code:

LOGENTRY="`date '+%b %d %k:%M:%S'` `hostname -s` `basename $0`:"
echo $LOGENTRY  something to log

Thanks in advance!

**Gustaf_Alhll** · February 28th, 2015

Make a loop and delay by using "sleep 1".
Ex.

Code:

while true; do
    LOGENTRY="`date '+%b %d %k:%M:%S'` `hostname -s` `basename $0`:"
    echo $LOGENTRY  something to log
    sleep 1
done

There are better ways to do it, but this is one way to.
Hope this helps!

**Lars Noodén** · February 28th, 2015

I'm pretty sure that there is not a way to use a regular environment variable in that way. I think you'd have to put it on a single line:

Code:

echo "$(/bin/date +'%b %d %k:%M:%S') $(/bin/hostname -s) $(/usr/bin/basename -- "$0"):" "something to log"

**fr33z0n3r** · February 28th, 2015

Rats! I have been playing with it since posting and discovered that by eliminating the VERY helpful variable, it was able to update.

I just figured linux is so powerful, why can't a variable actively evaluate again and again by default?

Is there some way to force evaluation? I've seen eval?

**ian-weisser** · February 28th, 2015

It's just a variable - an inert set of data bytes. It's not a class or a function or a method or anything active.

You can write a function to update the variable if you really want to.

Or you can write a function to create an updated timestamp string each time you need to log something.

**ofnuts** · February 28th, 2015

What you can do is keep the format in a variable to make sure that the same date format is used consistently. But considering that all logging goes also to the same file, if you want to make your logging simpler you write a function:

Code:

function log {
        printf "%s (%06d): %s\n" "$(date '+%F %H:%M:%S')" $$ "$*" >> /some/path/to/file.log
}

and in your code

Code:

log "this line will be logged"
log this line will be logged too

**fr33z0n3r** · March 3rd, 2015

@ofnuts - I thought I submitted my response, but I guess I missed that. I went with middle ground, but I will look to implement a simple function like you proposed. Its not painful. Thanks!