I'm new to linux. I want to be placed as a System Admin. I attended an interview at Amazon. They asked me to write a cmd to find the string that starts with 's' and ends with 'a' in a file. I jz know that we have to use grep, bt don't know the actual things. Added to this they also asked how grep works. Can anyone brief out an answer for this.
Thanks in advance
Try this GNU grep command with -P(Perl-regex) option,
grep -oP '\bs.*a\b' file
Explanation:
\b # Matches the word boundary(ie, match between a word character and a non word character)
s # Starting character would be a literal s.
.* # Matches any character zero or more times.
a # Matches a literal a.
\b # Matches the word boundary(ie, match between a word character and a non word character)
grep searches the named input FILEs (or standard input if no files are named, or if a single hyphen-minus (-) is given as file name) for lines containing a match to the given PATTERN. By default, grep prints the matching lines
Grep Commands
Grep and its Options
-v = non-matching lines
-c = count of matching lines
-i = Ignore case
-r = Read all files under each directory
-l = list the file which contain the searching keyword
^ = Search the Starting word of a file
.$ = Search the end word of a file
^$ = Search the empty lines in a file
Find all lines matching a specific keyword on a file.
grep sysadmin /etc/passwd
Display with numbers
grep -nv nologin /etc/passwd
To avoid the keyword and search for other
grep -v sysadmin /etc/passwd
To count how many lines match for the keywords we are searching
grep -c sysadmin /etc/passwd
To search text by ignoring the case
grep -i sysadmin /etc/passwd
Search all files in /home and its subdirectories for text matching a specific pattern and print the matching lines
grep -ri sysadmin /home/
Search all files in /home and its subdirectories for text matching a specific pattern and list the files which contain it
grep -ril sysadmin /home/
To search for a particular IP mentioned among many IPs. The -F ensures that the . match literal . characters, without it they would match any character.
grep -F "192.168.1.10" /var/log/syslog
To search for a line that starts with Feb
grep ^Feb /var/log/syslog
To search for a line that ends with queue
grep queue$ /var/log/mail.log
To count the empty lines in a file (lines containing whitespace will not be counted)
grep -c ^$ /var/log/mail.log
Search for a string inside all files of a directory and its subdirectories
grep -r "root" .
man grep, everything you need to know is there. – terdon Jun 17 '14 at 13:26