1. How do you write the contents of 3 files into a single file?
cat file1 file2 file3 > file
2. How to display
the fields in a text file in reverse order?
awk 'BEGIN {ORS=""} {
for(i=NF;i>0;i--) print $i," "; print "\n"}' filename
3. Write a command
to find the sum of bytes (size of file) of all files in a directory.
ls -l | grep '^-'| awk 'BEGIN
{sum=0} {sum = sum + $5} END {print sum}'
4. Write a command
to print the lines which end with the word "end"?
grep 'end$' filename
The '$' symbol specifies the
grep command to search for the pattern at the end of the line.
5. Write a command
to select only those lines containing "july" as a whole word?
grep -w july filename
The '-w' option makes the grep
command to search for exact whole words. If the specified pattern is found in a
string, then it is not considered as a whole word. For example: In the string
"mikejulymak", the pattern "july" is found. However
"july" is not a whole word in that string.
6. How to remove
the first 10 lines from a file?
sed '1,10 d' < filename
7. Write a command
to duplicate each line in a file?
sed 'p' < filename
8. How to extract
the username from 'who am i' comamnd?
who am i | cut -f1 -d' '
9. Write a command
to list the files in '/usr' directory that start with 'ch' and then display the
number of lines in each file?
wc -l /usr/ch*
Another way is
find /usr -name 'ch*' -type f
-exec wc -l {} \;
10. How to remove
blank lines in a file ?
grep -v ‘^$’ filename >
new_filename
11. Write a command
to remove the prefix of the string ending with '/'.
The basename utility deletes any
prefix ending in /. The usage is mentioned below:
basename /usr/local/bin/file
This will display only file
12. How to display
zero byte size files?
ls -l | grep '^-' | awk '/^-/
{if ($5 !=0 ) print $9 }'
13. How to replace
the second occurrence of the word "bat" with "ball" in a
file?
sed 's/bat/ball/2' < filename
14. How to remove
all the occurrences of the word "jhon" except the first one in a line
with in the entire file?
sed 's/jhon//2g' < filename
15. How to replace
the word "lite" with "light" from 100th line to last line
in a file?
sed '100,$ s/lite/light/' <
filename
16. How to list the
files that are accessed 5 days ago in the current directory?
find -atime 5 -type f
17. How to list the
files that were modified 5 days ago in the current directory?
find -mtime 5 -type f
18. How to list the
files whose status is changed 5 days ago in the current directory?
find -ctime 5 -type f
19. How to replace
the character '/' with ',' in a file?
sed 's/\//,/' < filename
sed 's|/|,|' < filename
20. Write a command
to find the number of files in a directory.
ls -l|grep '^-'|wc -l
For more questions like this please visit ----> Interview Questions : Unix/Linux
