I'm calling it "cxgrep" for context grep and to keep it from being confused with grep's -c switch. An alias that shows your discovered line along with the lines that appear before and after it in the file might look like this. $ pgrep '= \S+\s\S+\s' colorsĪnother very handy grep command is one that uses the -A (after) and -B (before) switches to provide some context for your located strings. In the example below, you can see that we're only matching color names that include three parts to the color names. I'm calling it plgrep (to avoid confusing it with pgrep). plgrepĪnother option that you'll find with the newer grep implementations is -P which interprets the pattern provided as a Perl regular expression. The choice depends on what you're looking for, though the use of -F offers a slight performance increase and no disadvantages when you're looking for straighht text. Note that we could have run this particular command without the -F option. The -f argument tells grep to get its patterns from the specified file rather than from the command line. When we then want to select from another file all of the lines that contain these color names. Say we have a list of colors in one file:
#Using grep examples series#
You can also put a series of literal strings in a file and look for them all using a command as in the example below. Here's an option that provides some interesting benefits. Because of this literalism, fgreg (i.e., grep -F) commands tend to run a little faster than oither grep commands. The $ in the command below, for example, is not taken as indicating that some kind of interpretation is needed. This means that it doesn't interpret any expressions that you specify, but takes them literally. With -F, grep interprets that patterns you provide as fixed strings. This means that you can provide a string of expressions that you want to match as shown in the example below. With the -E switch, grep uses extended regular expressions. So, you can use the options or set up the aliases to make using them a bit easier. They're just built into a single executable on most systems today. If you've used egrep and fgrep in the past, you'll find that grep -E and grep -F work as you'd expect. To easily switch from one mode of searching to another, the different grep commands could be set up as aliases such as these: alias egrep='grep -E' Historically provided as separate binaries, the different “flavors” of grep are now provided through a number of key command options that change how grep interprets the pattern that you provide for your search. It can take on some vastly different personalities that allow you to more cleverly find the data that you are looking for and has more flexibility than many of its users have discovered.
#Using grep examples full#
Search for full words not partial matches within words (-w) grep -w "fullstring" /home/ĩ.The grep command – likely one of the first ten commands that every Unix user comes to know and love – is not just a nice tool for finding a word or phrase in a file or command output. Display only the file names which matches the given pattern (-l) grep -rl "string" /home/Ĩ. Invert match (-v) grep -v 'root' /etc/passwdĭisplays the lines which does not matches the given stringħ. Search for the string ‘string’ in all the files in the home directory and all its subdirectories.Ħ. Recursive search (-r or -R) grep -r "string" /home/ Counting the number of matches (-c) grep -c 'root' /etc/passwdĥ. Showing matching line numbers (-n) grep -n 'root' /etc/passwdĤ. The wild card matches all files in the /etc/directoryģ.
Searching for a string in multiple files grep 'root' /etc/* Searching for a text string in one file grep 'root' /etc/passwdĢ. OK, now that we have the theory, let’s see some practical examples.ġ. The basic syntax of grep is: grep pattern target_file It can be very useful in your daily administration work on your Linux Cloud Hosting account. The name “grep” means “general regular expression parser” The grep command is used to search for text strings or regular expressions within one or more files.
Grep is one of the most used commands in Unix (or Linux).
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