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Tuesday, March 19, 2013

Unix Real Time Interview Questions with answers


1. Write a command to print the lines that has the the pattern “july” in all the files in a particular directory?
grep july *
This will print all the lines in all files that contain the word “july” along with the file name. If any of the files contain words like “JULY” or “July”, the above command would not print those lines.

2. Write a command to print the lines that has the word “july” in all the files in a directory and also suppress the filename in the output.
grep -h july *

3. Write a command to print the lines that has the word “july” while ignoring the case.
grep -i july *
The option i make the grep command to treat the pattern as case insensitive.

4. When you use a single file as input to the grep command to search for a pattern, it won’t print the filename in the output. Now write a grep command to print the filename in the output without using the ‘-H’ option.
grep pattern filename /dev/null
The /dev/null or null device is special file that discards the data written to it. So, the /dev/null is always an empty file.
Another way to print the filename is using the ‘-H’ option. The grep command for this is
grep -H pattern filename

5. Write a command to print the file names in a directory that does not contain the word “july”?
grep -L july *
The ‘-L’ option makes the grep command to print the filenames that do not contain the specified pattern.

6. Write a command to print the line numbers along with the line that has the word “july”?
grep -n july filename
The ‘-n’ option is used to print the line numbers in a file. The line numbers start from 1

7. Write a command to print the lines that starts with the word “start”?
grep ‘^start’ filename
The ‘^’ symbol specifies the grep command to search for the pattern at the start of the line.

8. In the text file, some lines are delimited by colon and some are delimited by space. Write a command to print the third field of each line.
awk ‘{ if( $0 ~ /:/ ) { FS=”:”; } else { FS =” “; } print $3 }’ filename

9. Write a command to print the line number before each line?
awk ‘{print NR, $0}’ filename

10. Write a command to print the second and third line of a file without using NR.
awk ‘BEGIN {RS=”";FS=”\n”} {print $2,$3}’ filename

11. How to create an alias for the complex command and remove the alias?
The alias utility is used to create the alias for a command. The below command creates alias for ps -aef command.
alias pg=’ps -aef’
If you use pg, it will work the same way as ps -aef.
To remove the alias simply use the unalias command as
unalias pg

12. Write a command to display todays date in the format of ‘yyyy-mm-dd’?
The date command can be used to display todays date with time
date ‘+%Y-%m-%d’

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