I don't think Snow Leopard's default setting is to use color for grep. I've had success on my OS X box with adding a line like alias grep=grep -color=always in my.bashrc to ensure consistent highlighting. Grep searches the named input FILEs (or standard input if no files are named, or the file name - is given) for lines containing a match to the given PATTERN. By default, grep prints the matching lines. In addition, two variant programs egrep and fgrep are available. Egrep is the same as grep -E. Fgrep is the same as grep -F.

– kill – background & example for OS X

– kill – is listed in my old AT&T UNIX SVR4 [ Rosen, p.201 ] book; so the command has been around for a long time. It seems to have been associated with processes and processes IDs early on. In fact, the recommended – kill – command looked like this in 1990s AT&T SVR4:

$ kill %3

where %3 was the process ID number; or ‘$ kill %troff’ which would stop the most recent troff job. So, what’s the philosophy of – kill – within OS X? The man page for – kill – reflects the historical usage in SVR4. But of course, OS X is a BSD derivative and we must also look at the ‘builtin’ functions descriptions:

– kill – is listed as both an External and a csh(1); but not usable in sh(1)

So, how can we use – kill -. Here is an example using our friend – grep –

Open your terminal and create a file of your current directory listing like so:

macintosh:~ yourusername$ ls – l >> ls2.txt

Now, since it is a .txt file containing directory listings, we can use grep to search for ‘-rw’; but beware – it may cause a warning…

macintosh:~ yourusername$ grep ‘-rw’ ls2.txt
grep: warning: recursive search of stdin

SOLUTION: Open another Terminal window and type the following:

macintosh:~ yourusername$ ps

You will get a listing something like this:

977 ttys001 0:00.01 -bash
985 ttys001 0:00.01 grep -rw ls2.txt
989 ttys002 0:00.01 -bash

So, just use another Terminal window command line to – kill – PID # 985

macintosh:~ yourusername$ kill 985

You should see a ‘Terminated’ indication in the other Terminal window and the command line will return! Success!

You can find grep present deep inside the animal brain of Unix and Unix-like operating systems. It is a basic program used for pattern matching and it was written in the 70s along with the rest of the UNIX tool that we know and love (or hate).

While learning about formal languages and regular expressions is an exciting topic. Learning grep has a lot more to it than regexes. To get started with it and to see the beauty and elegance of grep you need to see some real-world examples, first.

Examples which are handy and make your life a little easier. Here are 30 such grep commonplace use cases and options.

1. ps aux | grep <pattern>

The ps aux list all the processes and their associated pids. But often this list is too long for a human to inspect. Piping the output to a grep command you can list processes running with a very specific application in mind. For example the <pattern> could be sshd or nginx or httpd.

# ps aux | grep sshd
root 4000.00.2699445624 ? Ss 17:470:00 /usr/sbin/sshd -D
root 10760.20.3952046816 ? Ss 18:290:00 sshd: root@pts/0
root 10930.00.012784932 pts/0 S+ 18:290:00 grep sshd

2. Grepping your IP addresses

In most operating systems you can list all your network interfaces and the IP that is assigned to that interface by using either the command ifconfig or ip addr. Both these commands will output a lot of additional information. But if you want to print only the IP address (say for shell scripts) then you can use the command below:

$ ip addr|grep inet |awk'{ print $2; }'
$ ip addr|grep-w inet |awk'{ print $2; }'#For lines with just inet not inet6 (IPv6)

The ip addr command gets all the details (including the IP addresses), it is then piped to the second command grep inet which outputs only the lines with inet in them. This is then piped into awk print the statement which prints the second word in each line (to put it simply).

P.S: You can also do this without the grep if you know awk well know.

Grep Options

3. Looking at failed SSH attempts

If you have an Internet facing server, with a public IP, it will constantly be bombarded with SSH attempts and if you allow users to have password based SSH access (a policy that I would not recommend) you can see all such failed attempts using the following grep command:

# cat /var/log/auth.log | grep “Fail”
Sample out put
Dec 516:20:03 debian sshd[509]:Failed password for root from 192.168.0.100 port 52374 ssh2
Dec 516:20:07 debian sshd[509]:Failed password for root from 192.168.0.100 port 52374 ssh2
Dec 516:20:11 debian sshd[509]:Failed password for root from 192.168.0.100 port 52374 ssh2

4. Piping Grep to Uniq

Sometimes, grep will output a lot of information. In the above example, a single IP may have been attempting to enter your system. In most cases, there are only a handful of such offending IPs that you need to uniquely identify and blacklist.

The uniq command is supposed to print only the unique lines. The uniq -f 3 skips the first three fields (to overlook the timestamps which are never repeated) and then starts looking for unique lines.

5. Grepping for Error Messages

Using Grep for access and error logs is not limited to SSH only. Web servers (like Nginx) log error and access logs quite meticulously. If you set up monitoring scripts that send you alerts when grep “404” returns a new value. That can be quite useful.

# grep -w '404' /var/www/nginx/access.log
192.168.0.100 - - [06/Dec/2018:02:20:29 +0530]'GET /favicon.ico HTTP/1.1'404200
'http://192.168.0.102/''Mozilla/5.0 (Windows NT 10.0; Win64; x64)
AppleWebKit/537.36 (KHTML, like Gecko) Chrome/70.0.3538.110 Safari/537.36'
192.168.0.101 - - [06/Dec/2018:02:45:16 +0530]'GET /favicon.ico HTTP/1.1'404143
'http://192.168.0.102/''Mozilla/5.0 (iPad; CPU OS 12_1 like Mac OS X)
AppleWebKit/605.1.15 (KHTML, like Gecko) Version/12.0 Mobile/15E148 Safari/604.1'

The regex may not be “404” but some other regex filtering for only Mobile clients or only Apple devices viewing a webpage. This allows you to have a deeper insight at how your app is performing.

6. Package Listing

For Debian based systems, dpkg -l lists all the packages installed on your system. You can pipe that into a grep command to look for packages belonging to a specific application. For example:

7. grep -v <pattern> fileNames

To list all the lines which don’t contain a given pattern, use the flag -v. It is basically the opposite of a regular grep command.

8. grep -l <pattern>

It lists all the files that contain at least one occurrence of the supplied pattern. This is useful when you are searching for a pattern inside a directory with multiple files. It only prints the file name, and not the specific line with the pattern.

9. Single word option -w

The -w flag tells grep to look for the given pattern as a whole word and not just a substring of a line. For example, earlier we

Grep For Mac Os