write command in linux

We can broadcast message through terminal using wall command, but, what if we want to send a message to a particular used through terminal.

We can use write command for this.

root@host# w

18:23:38 up 10 days, 10:03, 2 users, load average: 0.17, 0.02, 0.22

USER TTY FROM LOGIN@ IDLE JCPU PCPU WHAT

root pts/0 xx.xx.xx.xx 10:48 0.00s 0.02s 0.03s -ksh

diju pts/3 xx.xx.xx.xx Tue18 17:18m 0.00s 0.01s sshd: diju [priv]

root@host# write diju pts/3

Hello are you working on the mail server issue, I am asked to troubleshoot the same.

root@host#

After typing “write diju pts/3" as the command hit enter key once.

Then type the message and hit ctrl+d to exit from the write session

Some commonly used SED oneliners

Commonly used SED one liners

# double space a file

sed G

# triple space a file

sed 'G;G'

# remove double-spacing

sed 'n;d'

# count lines

sed -n '$='

# convert DOS newlines (CR/LF) to Unix format

sed 's/.$//'

# delete leading whitespace (spaces, tabs) from begining of each line

sed 's/^[ \t]*//'

# delete trailing whitespace (spaces, tabs) from end of each line

sed 's/[ \t]*$//'

# delete BOTH leading and trailing whitespace from each line

sed 's/^[ \t]*//;s/[ \t]*$//'

# substitute "chit" with "chat" on each line

sed 's/chit/chat/' # replaces only 1st instance in a line

sed 's/chit/chat/2' # replaces only 2nd instance in a line

sed 's/chit/chat/g' # replaces ALL instances in a line

# substitute "chit" with "chat" ONLY for lines which contain "tea"

sed '/tea/s/chit/chat/g'

# substitute "chit" with "chat" EXCEPT for lines which contain "tea"

sed '/tea/!s/chit/chat/g'

# print first 5 lines of file

sed 5q

# print first line of file

sed q

# print last 10 lines of file

sed -e :a -e '$q;N;11,$D;ba'

# print last line of file

sed '$!d'

# print only lines which match regular expression

sed -n '/pattern/p'

or

sed '/patttern/!d'

# print only lines which do NOT match pattern

sed -n '/pattern/!p'

sed '/pattern/d'