Add (collect) exit codes in bash

问题:

I need to depend on few separate executions in a script and don't want to bundle them all in an ugly 'if' statement. I would like to take the exit code '$?' of each execution and add it; at the end, if this value is over a threshold - I would like to execute a command.

Pseudo code:

ALLOWEDERROR=5

run_something
RESULT=$?
..other things..

run_something_else
RESULT=$RESULT + $?

if [ $RESULT -gt ALLOWEDERROR ] 
   then echo "Too many errors"
fi

Issue: Even though the Internet claims otherwise, bash refuses to treat the RESULT and $? as integer. What is the correct syntax?

Thanks.

回答1:

You might want to take a look at the trap builtin to see if it would be helpful:

help trap

or

man bash

you can set a trap for errors like this:

#!/bin/bash

AllowedError=5

SomeErrorHandler () {
    (( errcount++ ))       # or (( errcount += $? ))
    if  (( errcount > $AllowedError ))
    then
        echo "Too many errors"
        exit $errcount
    fi
}

trap SomeErrorHandler ERR

for i in {1..6}
do
    false
    echo "Reached $i"     # "Reached 6" is never printed
done

echo "completed"          # this is never printed

If you count the errors (and only when they are errors) like this instead of using "$?", then you don't have to worry about return values that are other than zero or one. A single return value of 127, for example, would throw you over your threshold immediately. You can also register traps for other signals in addition to ERR.

回答2:

A quick experiment and dip into bash info says:

declare -i RESULT=$RESULT + $?

since you are adding to the result several times, you can use declare at the start, like this:

declare -i RESULT=0

true
RESULT+=$?
false
RESULT+=$?
false
RESULT+=$?

echo $RESULT
2

which looks much cleaner.

declare -i says that the variable is integer.

Alternatively you can avoid declare and use arithmetic expression brackets:

RESULT=$(($RESULT+$?))

回答3:

Use the $(( ... )) construct.

$ cat st.sh
RESULT=0
true
RESULT=$(($RESULT + $?))
false
RESULT=$(($RESULT + $?))
false
RESULT=$(($RESULT + $?))
echo $RESULT
$ sh st.sh
2
$

回答4:

For how to add numbers in Bash also see:

help let 

回答5:

If you want to use ALLOWEDERROR in your script, preface it with a $, e.g $ALLOWEDERROR.

回答6:

As mouviciel mentioned collecting sum of return codes looks rather senseless. Probably, you can use array for accumulating non-zero result codes and check against its length. Example of this approach is below:

#!/bin/sh

declare RESULT
declare index=0
declare ALLOWED_ERROR=1

function write_result {
    if [ $1 -gt 0 ]; then
        RESULT[index++]=$1
    fi
}

true
write_result $?

false
write_result $?

false
write_result $?

echo ${#RESULT[*]}
if [ ${#RESULT[*]} -gt $ALLOWEDERROR ] 
   then echo "Too many errors"
fi

回答7:

Here are some ways to perform an addition in bash or sh:

RESULT=`expr $RESULT + $?`
RESULT=`dc -e "$RESULT $? + pq"`

And some others in bash only:

RESULT=$((RESULT + $?))
RESULT=`bc <<< "$RESULT + $?"` 

Anyway, exit status on error is not always 1 and its value does not depend on error level, so in the general case there is not much sense to check a sum of statuses against a threshold.