simplify function call that writes to output stream and returns value

问题

This is a follow up question for write to output stream and returning value from shell script function.

In shell script, echo can be used to return values from functions. But, if those functions want to print some messages.

Then, this can be done by redirecting it to error stream.

But when the script is used as a autosys job. then messages from logic functions ends up in error stream file triggering alerts.

Is there any way, messages from logic function can be written to output stream and not mixing messages with return value.

Below is the solution suggested by James Brown :-

#this is a function that returns a value, as well as
#print some messages
function logic(){
    echo "start of logic"
    echo "perform logic, to get value"

    echo >&2 "logic done"

    echo "ok" >&4
}

function smain(){
    { local result=$( { { logic ; } 1>&3 ; } 4>&1); } 3>&1

    echo "result is >$result<"

    if [ "$result" == "ok" ];then
        echo "script successful"
    else
        echo "script failed"
    fi

    echo >&2 "end of smain"
}

smain

Now logic function is called at many places in our scripts. Above syntax is little too much too call logic. So, I tried adding helper functions(Return and sendReturnValue) to simplify this, but it's not working as expected.

Version 1

function sendReturnValue(){
  echo "$*" >&4
}

function Return(){
  { local result=$( { { sendReturnValue "$*" ; } 1>&3 ; } 4>&1); } 3>&1
  echo "$result"
}

#this is a function that returns a value, as well as
#print some messages                                                            
function logic(){
    echo "start of logic"
    echo "perform logic, to get value"

    echo >&2 "logic done"

    Return "ok"
}

function smain(){
    #{ local result=$( { { logic ; } 1>&3 ; } 4>&1); } 3>&1

    local result=$(logic)
    echo "result is >$result<"

    if [ "$result" == "ok" ];then
        echo "script successful"
    else
        echo "script failed"
    fi

    echo >&2 "end of smain"
}

smain

Version 2

Added getValue function :-

function getValue() {
    local fun=$1
    { local result=$({ { $fun; } 1>&3; } 4>&1); } 3>&1
    echo "$result"
}

#this is a function that returns a value, as well as
#print some messages
function logic() {
    echo "start of logic"
    echo "perform logic, to get value"

    echo >&2 "logic done"

    echo "ok" >&4
}

function smain() {
    #{ local result=$({ { logic; } 1>&3; } 4>&1); } 3>&1
    local result=$(getValue "logic")

    echo "result is >$result<"

    if [ "$result" == "ok" ]; then
        echo "script successful"
    else
        echo "script failed"
    fi

    echo >&2 "end of smain"
}

smain

Actual output of above two versions is same :-

$
sh returnValueWithEcho.sh > out.log 2>err.log

$
cat err.log
logic done
end of smain

$
cat out.log
result is >start of logic
perform logic, to get value
ok<
script failed

Expected output :-

$
sh returnValueWithEcho.sh > out.log 2>err.log

$
cat err.log
logic done
end of smain

$
cat out.log
start of logic
perform logic, to get value
result is >ok<
script successful

来源：https://stackoverflow.com/questions/62739537/simplify-function-call-that-writes-to-output-stream-and-returns-value

标签

function

shell

subprocess

stdout

stderr