sed examples

Ref: https://www.geeksforgeeks.org/sed-command-in-linux-unix-with-examples/

sed 's/unix/linux/' test.txt   # Replacing or substituting string (sed command replaces the first occurrence of the pattern in each line and it)

sed 's/unix/linux/2' test.txt  # Replacing the nth occurrence of a pattern in a line

sed 's/unix/linux/g' test.txt  # Replace all occurances in a line as well

sed 's/unix/linux/3g' test.txt # Replace nth till last (3rd, 4th, 5th etc.,)

echo "Welcome To The Geek Stuff" | sed 's/\(\b[A-Z]\)/\(\1\)/g'

sed '3 s/unix/linux/' test.txt # restrict the sed command to replace the string on a specific line number.

sed 's/unix/linux/p' test.txt  # The /p print flag prints the replaced line twice on the terminal. If a line does not have the search pattern and is not replaced, then the /p prints that line only once.

sed -n 's/unix/linux/p' test.txt # print only replaced lines, n option suppresses the duplicate rows generated by the /p flag and prints the replaced lines only one time.

sed '1,3 s/unix/linux/' test.txt # Replace range of lines

sed '5d' test1.txt  # delete 5th line

sed '$d' test1.txt  # delete last line

sed '3,6d' test1.txt # delete from range x to y

sed '12,$d' test1.txt # delete from nth line till last

sed '/abc/d' test1.txt # delete line which matches pattern

# Replace & update same file (-i means --in-place)

sed -i 's/ABC/ABCDEF/g' sed_test.txt

# Replace & update same file (-i means --in-place), -ibak takes original file as backup (sed_test.txtbak)

sed -ibak 's/ABC/ABCDEF/g' sed_test.txt

How to print first two columns of a file - AWK

1) It will print first line alone

>>awk 'NR==1' test.txt #1st line from the top
>>awk 'NR==7' test.txt #7th line from the top

2) How to print first line/lines of the file

>>head -8 test.txt

How to print last two columns of a file - AWK

1) How to print last two columns of a file?

NF => prints the last line

>>cat test.txt
prabhath   kota   Jan
lakshmi     muvvala   Feb
PRABHATH    KOTA   Mar
LAKSHMI       MUVVALA   Apr

>>awk '{print $(NF-1),"\t",$NF}' test.txt #RIGHT

output:
kota              Jan
muvvala         Feb
KOTA           Mar
MUVVALA  Apr

>>awk '{print $NF-1,"\t",$NF}' test.txt #WRONG


2) How to print last two columns of a command?

>> ls
-rw-r----- 1 kotaprax users 203 Nov 22 12:51 a.txt
-rw-r----- 1 kotaprax users 282 Nov 23 10:18 b.txt
-rw-r----- 1 kotaprax users  17 Nov 16 15:25 c.txt

>>ls -l | awk '{print $(NF-1),"\t",$NF}'

output:
12:51 a.txt
10:18 b.txt
15:25 c.txt


3) How to print the last line/lines of the file

>>tail -f test.txt
>>tail -4 test.txt #Prints Last 4 lines
>>tail -1 test.txt #Prints Last line of the file

Awk Examples

1) To fetch selected columns from a command using AWK

e.g.,

>> ls -l

-rw-r----- 1 kotaprax users 203 Nov 22 12:51 new.txt
-rw-r----- 1 kotaprax users 100 Nov 22 12:51 new1.txt
-rw-r----- 1 kotaprax users 126 Nov 23 12:57 output.txt
-rw-r----- 1 kotaprax users 282 Nov 23 10:18 test.txt
-rw-r----- 1 kotaprax users  17 Nov 16 15:25 test1.txt

From the abvoe command, we are deriving some columns

>> ls -l | awk '{print $3 "\t" $8 "\t" $9}'
             
kotaprax        12:51   new.txt
kotaprax        12:51   new1.txt
kotaprax        12:57   output.txt
kotaprax        10:18   test.txt
kotaprax        15:25   test1.txt



2) How to print first column from the file using AWK

e.g.,

>> cat test.txt
prabhath kota
lakshmi muvvala
PRABHATH KOTA
LAKSHMI MUVVALA


>>awk '{print $1}' test.txt
(or)
>>awk < test.txt '{ print $1 }'

o/p:
>>cat test.txt
prabhath
lakshmi
PRABHATH
LAKSHMI


3) How to copy the files using AWK

>> ls
a.txt
b.txt
c.txt

It will copy file.txt to file.txt.new for all the txt files

>>ls *.txt | awk '{print "cp "$1" "$1".new"}' | sh

o/p:

>> ls
a.txt
b.txt
c.txt
a.txt.new
b.txt.new
c.txt.new


4) How to list only directories using awk

>>ls
a.txt
b.txt
c.txt
prabhath_test

o/p:

>> ls -l | grep '^d'
#Lists only directories, since directories start with
drwxr-x--- 2 kotaprax users 1024 Nov 23 13:57 prabhath_test


>>ls -l | grep -v '^d' #Lists only files but not directories
-rw-r----- 1 kotaprax users 203 Nov 22 12:51 a.txt
-rw-r----- 1 kotaprax users 282 Nov 23 10:18 b.txt
-rw-r----- 1 kotaprax users  17 Nov 16 15:25 c.txt


5) Remove files using AWK

>>ls
a.txt
b.txt
c.txt
prabhath_test
a.tt
b.tt

>> ls -l *.tt | awk '{print "rm -r "$9}' | sh
#"rm" is a command, in order to execute, "sh" is used

o/p:

>>ls
a.txt
b.txt
c.txt
prabhath_test



6) AWK - Difference between $0 and $1

>> echo "hello1 hello2 hello3" | awk ' {print $0} ' #$0 prints the whole
hello1 hello2 hello3

>> echo "hello1 hello2 hello3" | awk ' {print $3} ' #$1 prints 1st column
hello3



7) How to print 1st column of a file into another file ?

>>cat test.txt
prabhath kota
lakshmi muvvala
PRABHATH KOTA
LAKSHMI MUVVALA

>> awk '{print $1}' test.txt > output.txt

o/p:

>>cat test.txt
prabhath
lakshmi
PRABHATH
LAKSHMI