BASH: print output on one line

Question

I've got this simple script below to stream compressed MySQL dumps to Amazon S3 bucket in parallel:

#!/bin/bash

COMMIT_COUNT=0
COMMIT_LIMIT=2

for i in $(cat list.txt); do

        echo "$i "

        mysqldump -B $i | bzip2 -zc | gof3r put -b s3bucket -k $i.sql.bz2 &


        (( COMMIT_COUNT++ ))

        if [ ${COMMIT_COUNT} -eq ${COMMIT_LIMIT} ]; then
        COMMIT_COUNT=0
        wait
        fi

done

if [ ${COMMIT_COUNT} -gt 0 ]; then
        wait
fi

The output looks like this:

database1 
database2 
duration: 2.311823213s
duration: 2.317370326s

Is there a way to print this on one line for each dump?

database1 - duration: 2.311823213s
database2 - duration: 2.317370326s

The echo -n switch doesn't help in this case.

EDIT: Wed May 6 15:17:29 BST 2015

I was able to achieve expected results based on accepted answer:

echo "$i -" $(mysqldump -B $i| bzip2 -zc | gof3r put -b s3bucket -k $i.sql.bz2 2>&1) &

- however a command that is running in a subshell is not returning exit status to a parent shell because it's running in parallel so I'm not able to verify if it succeed or failed.

Answer 1

I think this command will do what you want:

echo "$i -" `(mysqldump -B $i | bzip2 -zc | gof3r put -b s3bucket -k $i.sql.bz2) 2>&1` &

Or, use $() in place of backticks :

echo "$i -" $( (mysqldump -B $i| bzip2 -zc | gof3r put -b s3bucket -k $i.sql.bz2) 2>&1 ) &

The echo command will wait for mysqldump .. result to finish before try to print together with $i. The sub-shell ( … ) and error redirection 2>&1 ensure that error messages go into the echoed output too. The space after the $( is necessary because $(( without a space is a different special operation — an arithmetic expansion.

Answer 2

Thanks for all your help but I think I've finally found an optimal solution for this.

Basically I used xargs to format the output so each entry (dump name + duration time) is on one line. I also added the job spec to wait command to get the exit status:

man bash

wait [n ...] Wait for each specified process and return its termination status. Each n may be a process ID or a job specification; if a job spec is given, all processes in that job's pipeline are waited for. If n is not given, all currently active child processes are waited for, and the return status is zero. If n specifies a non-existent process or job, the return status is 127. Otherwise, the return status is the exit status of the last process or job waited for.

Test:

# sh -c 'sleep 5; exit 1' &
[1] 29970
# wait; echo $?
0
# sh -c 'sleep 5; exit 1' &
[1] 29972
# wait $(jobs -p); echo $?
1

Final script:

#!/bin/bash

COMMIT_COUNT=0
COMMIT_LIMIT=2


while read -r i; do

    mysqldump -B $i | bzip2 -zc | gof3r put -b s3bucket -k $i.sql.bz2 |& xargs -I{} echo "${DB} - {}" &

    (( COMMIT_COUNT++ ))

    if [ ${COMMIT_COUNT} -eq ${COMMIT_LIMIT} ]; then
        COMMIT_COUNT=0
        wait $(jobs -p)
    fi

done < list.txt

if [ ${COMMIT_COUNT} -gt 0 ]; then
     wait $(jobs -p)
fi

if [ $? -ne 0 ]; then
     echo "ERROR: Backups failed"
     exit 1
fi