How to use pipes to connect programs
- Use the vertical bar (|) between two commands. In this example, send ls command output to grep command i.e. find out if data.txt file exits or not in the current working directory):
ls | grep "data.txt"
- All command line arguments (parameters) listed after command name, but before the the vertical bar:
ls -al | grep "data.txt"
- There is no need to put spaces between command names and vertical bars, it is optional:
ls -al|grep "data.txt"
- However, I recommend putting white spacing between the command names and vertical bars to improve the readability.
- You can redirect pipe output to a file (output redirection with > symbol):
ps aux | grep httpd > /tmp/ps.output.log
Common shell pipe examples:
Pause ls command output
ls -l | more
Show a sorted list of logged on users
Output of who command is given as input to sort command. So that it will print a sorted list of users:
who | sort who | sort > sorted_list.txt
Count logged in users
Output of who command is given as input to wc command, so that it will number of user who logged on to the system:
who | wc -l
Find out if user vivek logged in or not
who | grep -i vivek
Count total files in current directory
ls -l | wc -l
Execute a shutdown command at a given time
echo "shutdown -h now" | at 12am tomorrow
Format output of mount command
Display mount command output in a nice format
mount | column -t
Backup (tar over ssh)
Use tar command over secure ssh session to backup local /home file system:
tar zcvf - /home | ssh user@server "cat > /backup/home_fs.workstation_sep_21_09.tar.gz"
v="Unix Philosophy"; echo $v | tr '[:lower:]' '[:upper:]' echo 'tHIs IS A TeSt' | tr '[:upper:]' '[:lower:]'
Birthday Email Reminder
echo "/usr/bin/mail -s 'Birthday gift for Julia' firstname.lastname@example.org < /dev/null" | at 17:45
Create An ISO CD Image
Create an ISO cdrom image from contents of /home/vivek/photos directory:
mkisofs -V Photos -r /home/vivek/photos | gzip -9 > /tmp/photos.iso.cd.gz
You can burn an ISO cdrom image using the following syntax:
gzip -dc /tmp/photos.iso.cd.gz | cdrecord -v dev=/dev/dvdrw -
It is also possible to create an ISO image and burn it directly to cd:
mkisofs -V Photos -r /home/vivek/photos | cdrecord -v dev=/dev/dvdrw -
Create a random password
tr -dc A-Za-z0-9_ < /dev/urandom | head -c12 | xargs