Sed/Awk Top Commands(Unix interview questions)

In this post i will mention very useful sed/awk commands,These are quite handy in day to day work and also useful in unix interview.

How to Print only Blank Line of File.

sed -n '/^$/p' Test_file.txt

To Print First and Last Line using Sed Command

sed  -n ‘1p’ Test_file.txt

sed –n ‘$p’ Test_file.txt

To Print all line Except First Line

sed –n ‘1!p’ Test_file.txt

Delete all Line except First Line

sed –n ‘1!d’ Test_file.txt

How to get only Zero Byte files which are present in the directory

ls -ltr| awk '/^-/ { if($5 ==0) print $9 }'

How add a First record and Last Record to the current file in Linux

sed -i -e '1i Header' -e '$a Trailor' test_file.txt

How to display Even number of records into one file and Odd number of records into another file

awk 'NR %2 == 0' test_files.txt

awk 'NR %2 !=  0' test_files.txt

Remove all empty lines:

sed '/^$/d' test_file.txt

sed '/./!d' test_file.txt

Add at start of line :
awk '{print "START"$0}' FILE 

Add at end of line :
awk '{print $0"END"}' FILE 

Too see a particular line

For example if you just want to see 180th line in file sed -n '180p' testfile.txt

To find a particular column in file 

cat testfile.txt |awk -F"," '{print $2}'

To rename file with current date 

mv test test_`date +%Y-%m-%d

Command to take out all those lines which are having 8 at 17th position 
grep '^.\{16\}8' testfile.txt >testfile_new.txt

To remove nth line without openning file 
sed 'nd' file1>file2 to remove multiple lines sed -e 1d -e 5d

To find top 20 files with most space

ls -ltr|awk -F" " '{print $5 $9}' sort -ntail -20

To find record in first file not in second 
comm -13 testfile1.txt testfile2.txt

If you are looking from something that is contained in a file but you don't know which directory it is in do the following:
find . -name "*" xargs grep -i something This will find all of the files in the directory and below and grep for the string something in those files!

Delete Files Delete all the files starting with name testfile 

find . -type f -name "testfile*" exec rm -f {} \;

Remove blank space from file 

sed -e "s/ *//g" testfile.txt >testfile.txt_wo_space

How to do grep on large number of files in a direcory 

Normally you get the error "grep argument list too long" if you try to do grep in directory having large number of files ,It can be avoided by using it in below manner

grep -rl "Search Text" /tmp


How to do count of lines in ebicdic file 

dd if=ebcdic_file bs=$REC_SIZE > /dev/null