Grep is one of the important command that you should learn thoroughly. But why and how did it get its name? Professor Brian Kernighan explains the etymology of grep in this video.Īnd, that's all. Grep was written overnight by Ken Thompson, the same guy who wrote Unix. It simply ignores the dollar symbol (the special character, of course) and displays the word that contains the string "o$".įor more details about grep, type: $ grep -help Since there were no characters ends with "o" in file.txt, we get nothing. To search for the words that matches the string "o$" with grep command, we do: $ grep o$ file.txtīut, we get nothing, why? Because, as per the above command, we use the dollar symbol($) to find the words that ends in "o". It will display nothing, because it couldn't evaluate the special characters.
fgrep can be used where you want regular expressions to be evaluated.įor example, we use the following command to find the words end in "x". fgrep can't recognize regular expressions or special characters. Fgrep command examplesįgrep stands for fast grep. See? Now we have got the words that begins with the character range "l" to "u" (either upper or lower case). To display all the lines that starts with both upper and lower case letters, we use: $ egrep '^|' file.txt Since grep is case-sensitive, it is not going to find lines that starts with uppercase letters in the given range. Please note that I have used square bracket ([) to search for the range of words. Everything else will be omitted from the result. That means, we will get the lines that start with l, m, n, o, p, q, r, s, t, and u. Similarly, We can search for the lines that start with any character range between "l" to "u". Please note that the normal grep command can't do this. See? We have got all of the words that starts with either "l" or "o". Hence, our command for the above query will be: $ egrep '^(l|o)' file.txt Remember we use caret symbol (^) to search words at the beginning of line. However, It provides some additional functionalities, such as using complicated regex, than the normal grep command does out of the box.įor instance, we can search for any words that start with either "l" or "o". It will do all the things that grep will do. Egrep command examplesĮgrep stands for extended grep. Let us go ahead and learn the other two variants, namely egrep and fgrep.
You should now have a basic understanding of grep usage. (dot).įor example, let us search for any word that has "n" in the file. $ grep x$ file.txtĪlso, you can find the words that contains any character using. Similarly, we can search for the words that ends with a particular letter(s), for example "x", like below. To search for the words that matches the pattern "tech" at the beginning of the line in a file, run: $ grep ^tech file.txt This is where special characters comes in handy. You don't want to display all the words that contains the string, but only the words that have the string "tech" at the beginning. $ grep tech file.txtīut what if you just wanted to search for the lines that only start with the word "tech". You know already, we can search for the words that contains the string "tech" like below.
#Grep manual how to#
Let me show you an example, so you can understand where and how to use those special characters. ^ - search at the beginning of the line.We can also use some special characters or regular expressions in grep. The output of the file.txt is piped into grep and the words that contains the letters "os" in file.txt have been displayed. We can also pipe an output of a command into grep. Now, grep didn't care about the case and we got the words that contains both uppercase and lowercase letters in the result. Ostechn1x $ grep -i 'hello world' file.txt If you want, however, to ignore case sensitive, you can use "-i" flag like below.
$ grep os file.txtīut, I have another word named "Ostechnix" in file.txt, but grep didn't list it. For example, when you search for "os", it is not going to display lines the contains uppercase letters i.e Os.Ĭheck the following example. This can be useful when you're working with a really long code. You can also use -n flag to show the line numbers in the output: $ grep -n nix file.txt If the search string has two words, mention them inside single quotes like below. To do so, I run: $ grep nix file.txtĪs you see in the above output, we got two words that contains the matching pattern "nix". For example, I am going to look for the string "nix" in file.txt. To begin the search, just type grep followed by what it is you're looking for and where you are looking from.
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