Strange output in shell script - linux

Question

I'm encountering a very strange thing while writing a shell script.
Initially I have the following script.
OUTPUT_FOLDER=/home/user/output
HOST_FILE=/home/user/host.txt
LOG_DIR=/home/user/log
SLEEPTIME=60
mkdir -p $OUTPUT_FOLDER
while true
do
rm -f $OUTPUT_FOLDER/*
DATE=`date +"%Y%m%d"`
DATETIME=`date +"%Y%m%d_%H%M%S"`
pssh -h $HOST_FILE -o $OUTPUT_FOLDER
while read host
do
numline=0
while read line
do
if [[ $numline == 0 ]]
then
FIELD1=`echo $line | cut -d':' -f2 | cut =d' ' -f2`
fi
((numline+=1))
done < ${OUTPUT_FOLDER}/${host}
echo "$DATETIME,$FIELD1" >> ${LOG_DIR}/${DATE}.log
done < $HOST_FILE
sleep $SLEEPTIME
done
When I ran this script, every 60 seconds, I'll see the $DATETIME,$FIELD1 values in my log file.
What is very strange, is that every 30 seconds or so, after the first minute has passed, I'll see 20160920_120232,, meaning there was output where there shouldn't be, and I guess because I deleted the contents of my output folder, FIELD1 is empty.
What is even more strange, is while trying to debug this, I added a few more echo statements to print to my log file, and then I deleted those lines. However, they continued to be printed every 30 seconds or so, after the first minute has passed.
What is stranger still is that I then commented out everything inside the while true block, that is,
OUTPUT_FOLDER=/home/user/output
HOST_FILE=/home/user/host.txt
LOG_DIR=/home/user/log
SLEEPTIME=60
mkdir -p $OUTPUT_FOLDER
while true
do
: << 'END'
rm -f $OUTPUT_FOLDER/*
DATE=`date +"%Y%m%d"`
DATETIME=`date +"%Y%m%d_%H%M%S"`
pssh -h $HOST_FILE -o $OUTPUT_FOLDER
while read host
do
numline=0
while read line
do
if [[ $numline == 0 ]]
then
FIELD1=`echo $line | cut -d':' -f2 | cut =d' ' -f2`
fi
((numline+=1))
done < ${OUTPUT_FOLDER}/${host}
echo "$DATETIME,$FIELD1" >> ${LOG_DIR}/${DATE}.log
done < $HOST_FILE
sleep $SLEEPTIME
END
done
Even with this script, where I'm expecting nothing to be printed to my log file, I see my previous echo statements that I have deleted, and the lines with the empty FIELD1. I have checked that I'm running the correct version of the script each time.
What is going on?

Answer 1

Am not sure, it could be a the actual reason for the screw-up. You have an incorrect usage of cut in line number 22 which could have mangled the FIELD1 inadvertently.
FIELD1=`echo $line | cut -d':' -f2 | cut =d' ' -f2`
# ^ incorrect usage of the delimiter '-d' flag
which should have been used as
FIELD1=`echo $line | cut -d':' -f2 | cut -d' ' -f2`
# ^ Proper usage of the '-d' flag with space delimiter
I tried to capture the piped command output to see if the last command could have succeeded and below was my observation.
echo $line | cut -d':' -f2 | cut =d' ' -f2;echo "${PIPESTATUS[#]}"
cut: =d : No such file or directory # --> Error from the failed 'cut' command
0 0 1 # --> Return codes of each of the command being piped
Also, if you have been a bash purist, you have avoided the legacy `` style command expansion and used a $(cmd) syntax like,
FIELD1=$(echo "$line" | cut -d':' -f2 | cut -d' ' -f2)
Another simpler way would have been to avoid use of cut & echo and do pure bash string-manipulation.
Assuming your $line contains : and de-limited string e.g."What Hell:Hello World" and you are trying to extract the World part as I could see, just do
FIELD1="${line##* }" # Strips-off characters until last occurrence of whitespace

Answer 2

I tried to reproduce it and couldn't. Thre is no reason for this script (when commented as you have) to produce any output.
There are couple of cases:
As others pointed out, there may be some other script writing to your log file
You may have left few instances of this script running on other terminals
You may be running this script from crontab once every 5 mins
In order to rule out possibilities, do a "ps -aef" and check out all the processes that could resemble the name of your script. To catch things from crontab, you may have to watch the output of "ps -aef" a big longer (or just check in the crontab entries).