Errors with a shell-script

Question

i found some freaky error. I want to increment a counter, but the variable isnt visible outside the while do.

The script as follows:

    ## $1 - The file which should be examined
## $2 - The time passed between the checks. If $2 is 5 then all lines from the last 5 minutes are taken
## $3 - The Errormessage to search for

outputOK="OK - nothing happened"
output_logcheck=0;
errlines="";

cat $1 | grep "$3" | while read line
do
        linedate=`date -d "$(echo $line | cut -d " " -f 2)"  '+%s'`
        nowdate=`date '+%s'`

        if [ $(( $nowdate - (60 * $2) )) -le $linedate ]
        then
                $output_logcheck=$[$output_logcheck+1]
                $errlines="${errlines} -- ${line}"
        fi
done;

if [ $output_logcheck -eq 0 ]
then
        echo $outputOK
else
        echo "CRITICAL - There are -= ${output_logcheck} =- $3 -- Lines: $errlines"
fi

So i dont know what else to try. Thanks in advance.

There is a FAQ entry about this problem, just for future reference: "I set variables in a loop that's in a pipeline. Why do they disappear after the loop terminates? Or, why can't I pipe data to read?" — user725091
– user725091, Commented Dec 12, 2011 at 13:04

kev · Accepted Answer · 2011-12-20 06:59:58Z

2

The problem is that pipe create a SubShell.

change

cat $1 | grep "$3" | while read line
do
    ...
done

to

while read line
do
    ...
done <(cat $1 | grep "$3")

edited Dec 20, 2011 at 6:59

answered Dec 12, 2011 at 14:00

kev

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JRFerguson · Accepted Answer · 2011-12-13 00:30:50Z

1

As noted, the Bash shell, creates a subshell whenever a pipe is opened to a loop. In that case, variables within the loop are local to the loop.

One kludge is to substitute (if possible) a Korn ('ksh') shell for the Bash one.

answered Dec 13, 2011 at 0:30

JRFerguson

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1 Comment

Zac Thompson Over a year ago

I'd argue that this is not a kludge, and is in fact one of the key strengths of ksh for shell programming

Ahmed Masud · Accepted Answer · 2011-12-12 13:02:33Z

Try something like:

## $1 - The file which should be examined
## $2 - The time passed between the checks. If $2 is 5 then all lines from the last 5 minutes are taken
## $3 - The Errormessage to search for

outputOK="OK - nothing happened"
outfile="/tmp/result.$$"

trap { rm $outfile } 0 1 2 3

cat $1 | grep "$3" | (output_logcheck=0; errlines=""; while read line
do
        linedate=`date -d "$(echo $line | cut -d " " -f 2)"  '+%s'`
        nowdate=`date '+%s'`

        if [ $(( $nowdate - (60 * $2) )) -le $linedate ]
        then
                $output_logcheck=$[$output_logcheck+1]
                $errlines="${errlines} -- ${line}"
        fi
done; echo $output_logcheck ":" $errlines > $outfile)

output_logcheck=`cat $outfile| cut -f1 -d:`
errlines=`cat $outfile|cut -f2 -d:`

if [ $output_logcheck -eq 0 ]
then
        echo $outputOK
else
        echo "CRITICAL - There are -= ${output_logcheck} =- $3 -- Lines: $errlines"
fi

mouviciel · Accepted Answer · 2011-12-12 13:03:07Z

0

while is executed in a separate process. Variables that are changed in the context of that process still hold their unchanged valus in the parent process.

answered Dec 12, 2011 at 13:03

mouviciel

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