Shell script function to execute command with pipe and redirect stdout and stderr to variable

Question

I have written a common function to execute any given command and fetch stdout and stderr to a variable. However, command with pipe doesn't work properly.

I also tried with eval however, unable to redirect stdout/stderr to a variable

Here is my function

LOGFILE="mylog.txt"

Log() {
    msg=$2
    level=$1
    timestamp=`date "+[%F %T]"`
    echo ""
    echo "" >> $LOGFILE
    echo "$timestamp [$level] ==> $msg"
    echo ""
    echo "$timestamp [$level] ==> $msg" >> $LOGFILE
    echo "" >> $LOGFILE
}

RunCommand() {
    CMD=$1
    MSG1=`printf "Executing command \nCommand: $1"`

    OUTPUT=`$CMD 2>&1`
    ERRCODE=`echo $?`

    MSG2=`printf "\n\nOutput: \n%s" "${OUTPUT}"`
    MSG3=`printf "\n\nError Code: %s\n%s" "${ERRCODE}"`
    Log INFO "${MSG1}${MSG2}${MSG3}"
}

command="df -h | grep /$"
RunCommand "$command"

Output:

[2019-05-02 05:01:29] [INFO] ==> Executing command
Command: df -h | grep /$

Output:
df: '|': No such file or directory
df: grep: No such file or directory
df: '/$': No such file or directory

Error Code: 1

Other commands are working without any error. Executed script with another long command.

[2019-05-02 05:10:20] [INFO] ==> Executing command
Command: find /var/bundle/upgrade/ -type f -size +1b

Output:
/var/bundle/upgrade/upgrade.sh
/var/bundle/upgrade/run_task.py
/var/bundle/upgrade/lib/UpgradeTask.pyc
/var/bundle/upgrade/lib/Constants.pyc
/var/bundle/upgrade/lib/Constants.py
/var/bundle/upgrade/lib/UpgradeTask.py
/var/bundle/upgrade/util/FileSystem.pyc

Error Code: 0

You are trying to put a compound command in a variable. Have a look at "I'm trying to put a command in a variable, but the complex cases always fail!" — John1024
– John1024, Commented May 2, 2019 at 6:02
Also, have a look at: "Why should eval be avoided in Bash, and what should I use instead?" — John1024
– John1024, Commented May 2, 2019 at 20:45

Sanwolverine · Accepted Answer · 2019-05-02 06:30:36Z

1

check if below changes work for you

RunCommand() {
    CMD=$1
    MSG1=`printf "Executing command \nCommand: $1"`

    OUTPUT=$(eval "$CMD 2>&1")
    ERRCODE=`echo $?`

    MSG2=`printf "\n\nOutput: \n%s" "${OUTPUT}"`
    MSG3=`printf "\n\nError Code: %s\n%s" "${ERRCODE}"`
    Log INFO "${MSG1}${MSG2}${MSG3}"
}

edited May 2, 2019 at 6:30

answered May 2, 2019 at 6:23

Sanwolverine

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R4444 · Accepted Answer · 2019-05-02 06:39:10Z

0

A small fix :-)

You forgot to add eval

LOGFILE="mylog.txt"

Log() {
    msg=$2
    level=$1
    timestamp=`date "+[%F %T]"`
    echo ""
    echo "" >> $LOGFILE
    echo "$timestamp [$level] ==> $msg"
    echo ""
    echo "$timestamp [$level] ==> $msg" >> $LOGFILE
    echo "" >> $LOGFILE
}

RunCommand() {
    CMD=$1
    MSG1=`printf "Executing command \nCommand: $1"`

    OUTPUT=`$CMD 2>&1`
    ERRCODE=`echo $?`

    MSG2=`printf "\n\nOutput: \n%s" "${OUTPUT}"`
    MSG3=`printf "\n\nError Code: %s\n%s" "${ERRCODE}"`
    Log INFO "${MSG1}${MSG2}${MSG3}"
}

command="df -h | grep /$"
eval RunCommand "$command"

Output on my machine:

/dev/sda3 152658276 92448632 52432648 64% /

answered May 2, 2019 at 6:39

R4444

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