run command concurrently within script

[yc_2]

Hi,

Is it possible to write a script to run multiple commands concurrently? Example: perform fsck for a few file systems.

Thanks in advance

[Steven E. Protter · Accepted solution]

Shalom,

Yes


#!/bin/ksh

command1 &
command2 &
command3 &



Doing this with fsck might cause I/O to go high, but it should work.

SEP

[yc_2]

Any way to capture the output since it is in back ground?

[Torsten.]

Try

# command1 >/tmp/command1.out 2>/tmp/command1.out &

BTW, fsck on a newly created filesystem is maybe not needed and will return very quickly.

[yc_2]

Thanks. I will try it out. The fsck is use for true copy purpose.

[yc_2]

Why pipe 2 times to the same file?

# command1 >/tmp/command1.out 2>/tmp/command1.out &

[Torsten.]

One ">" was missing, sorry.

# command1 >/tmp/command1.out 2>>/tmp/command1.out &

But you can use different files, of course.

[Bill Hassell]

> # command1 >/tmp/command1.out 2>>/tmp/command1.out &

This is a better way if all output (stdout and stderr must go into the same file):

cmd1 > /tmp/cmd1.log 2>&1 &
cmd2 > /tmp/cmd2.log 2>&1 &

The construct 2>&1 says: take stderr (file number 2) and redirect it into file number 1. Each time the command runs, it will clear the log file. To track all runs of the command, change > to >> as in:

cmd1 >> /tmp/cmd1.log 2>&1 &
cmd2 >> /tmp/cmd2.log 2>&1 &

For cumulative logs, be sure to add a timestamp, especially one that can be easily sorted or selected such as YYYYMMDD.HHMMSS. You can add this to your scripts:

echo "$(date +%Y%m%d.%H%M%S) and sime text..."

Or for applications that you can't modify, add the timestamp before running the program:

echo "$(date +%Y%m%d.%H%M%S)" >> cmd1.log; cmd1 >> /tmp/cmd1.log 2>&1 &
echo "$(date +%Y%m%d.%H%M%S)" >> cmd1.log; cmd2 >> /tmp/cmd2.log 2>&1 &