bash: syntax error: operand expected (error token is "-")

Question

I am trying to watch a log for certain messages within the last hour. The logs are formatted in this manner:

[1/18/19 9:59:13:791 CST] <Extra text here...>

I was having trouble with just doing a date comparison with awk, so my thought was to convert to epoch and compare. I am taking field 1 and cutting off the milliseconds from field 2, and removing [] (though I guess I could just do [ for my purposes).

while read -r line || [[ -n "$line" ]]
do
    log_date_str="$(awk '{gsub("\\[|\\]", "");print $1" "substr($2,1,length($2)-4)}' <<< "$line")"
    log_date="$(date -d "$log_date_str" +%s)"
    [[ $(($(date +%s)-$log_date)) -le 3600 ]] && echo "$line"
done < /path/to/file

When I try to run this against the log file though, I get this error:

date: invalid date `************ S'
-bash: 1547832909-: syntax error: operand expected (error token is "-")

Taking a single date, e.g. "1/18/19 9:59:13" works with the date conversion to epoch, but I'm not sure where to go with that error.

Running `bash -x yourscript` will let you see the commands as they're actually run, with the variables' real-world values; that makes it a lot easier to isolate what's going on, especially here where we don't know what your `line` contains, or what `log_date_str` or `log_date` values are in practice. — Charles Duffy, Jan 18 '19 at 17:57
That said, I **really** don't know why you'd mix arithmetic and extended-test syntax this way. `(( ( $(date +%s) - log_date ) <= 3600 )) && echo "$line"` is less syntax. — Charles Duffy, Jan 18 '19 at 17:58
Moreover, your code **doesn't** cause the stated error with only the line of input you provided; see it running correctly (and choosing not to print anything, but *not* throwing any error) at https://ideone.com/e57xWm. Please try to follow the [mcve] definition in your code samples so others can actually see the problem you're asking about for themselves, and test their answers. — Charles Duffy, Jan 18 '19 at 18:00
It looks like there's a log line that begins with like `************ S` instead of the date and time. You need to filter out lines that don't follow the expected format. — Barmar, Jan 18 '19 at 18:08
That looks like the problem Barmar, I had been originally working with cat then grepping for a certain error, then trying to use awk. Didn't even cross my mind that I'm getting the entirety of the log using this method instead now. — wafflenator, Jan 18 '19 at 18:14
Charles, thanks for the feedback! I was basing it on https://stackoverflow.com/questions/35880325/how-to-accurately-grab-logs-in-the-past-hour-from-a-log-file-in-bash — wafflenator, Jan 18 '19 at 18:15
Also see [How to use Shellcheck](http://github.com/koalaman/shellcheck), [How to debug a bash script?](http://unix.stackexchange.com/q/155551/56041) (U&L.SE), [How to debug a bash script?](http://stackoverflow.com/q/951336/608639) (SO), [How to debug bash script?](http://askubuntu.com/q/21136) (AskU), [Debugging Bash scripts](http://tldp.org/LDP/Bash-Beginners-Guide/html/sect_02_03.html), etc. — jww, Jan 18 '19 at 18:42

score 0 · Answer 1 · answered Jan 18 '19 at 19:05

As the comments pointed out, I was getting data that was not a date since it was parsing the entire log. Grepping the input file for my desired text solved my problems, and I've changed to Charles' suggestion.

while read -r line || [[ -n "$line" ]]
do
    log_date_str="$(awk '{gsub("\\[|\\]", "");print $1" "substr($2,1,length($2)-4)}' <<< "$line")"
    log_date="$(date -d "$log_date_str" +%s)"
    (( ( $(date +%s) - log_date ) <= 3600 )) && echo "$line"
done < <(grep ERROR_STRING /path/to/file.log)

bash: syntax error: operand expected (error token is "-")

1 Answers1