Oracle UNIX pipe command

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Don Burleson Blog

Oracle UNIX pipe command

Oracle Database Tips by Donald Burleson

Oracle UNIX pipe command

The pipe command is one of the most important commands in UNIX because it allows us to create powerful functions in a single statement. The pipe command is represented with the | character and it is used to "connect" the output from one command and send it as input to another command.

For example, suppose we want to list the distinct file owners in a directory. To do this, we must perform three discrete tasks:

1. We must list all files in the directory (ls –al)
2. We must parse this output and extract the file owner from the fourth column of the output. (awk '{ print $3 }')
3. We must then take the list of file owners and remove duplicate entries (sort –u)

Using the pipe command, we can tie these three functions together into a single UNIX command, piping the output from one command as sending it as input to the next UNIX command:

root> ls -al|awk '{ print $3 }'|sort -u

marion
oracle
root

Let's take a closer look at how this works

First, we execute the ls –al command to get the fill details for each file in the directory

root> ls -al
total 928188
drwxr-xr-x 21 oracle dba 2048 Aug 22 20:47 .
drwxr-xr-x 10 root root 512 Jul 26 08:49 ..
-rw------- 1 oracle qmail 71 Sep 1 2000 .TTauthority
-rw------- 1 oracle dba 254 Feb 20 2001 .Xauthority
-rw------- 1 oracle qmail 437 Aug 12 20:43 .bash_history
drwxr-xr-x 11 oracle qmail 512 Sep 3 2000 .dt
-rwxr-xr-x 1 oracle qmail 5111 Sep 3 2000 .dtprofile

2 - Next, pipe the output from this command to the awk utility to only display the owner of each file:

cheops*envtest-/export/home/oracle
root> ls -al|awk '{ print $3 }'

oracle
root
oracle
oracle
oracle
oracle
oracle
oracle
oracle
oracle
oracle

3 - Finally, we pipe the owner list to the UNIX sort command to remove duplicate entries:

root> ls -al|awk '{ print $4 }'|sort -u

dba
other
qmail
root

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