Now you can search all of them together with grep using the “-R” command. To make things easy for you, you create a new folder containing symbolic links to all the various log files that are of interest to you. After all, many packages have their own locations for log files. Let’s say for example, that you have a bunch of log files scattered all around the system. However, we can also use it to search an entire directory of files at the same time.

We normally think of grep searching either a file or a specific output from another command. Searching an Entire Directory for a Match and Showing the File Name If you want to remove the “words” requirement and instead just want a straight up string match, then you can drop the “w” parameter. We can match as many words as we need to that way. So the above command becomes: egrep -w 'sparrow|dogs' animal-count To make it even easier, we can just replace “grep -E” with “egrep”. -w means that we only want to match whole words.-E means that we’re using extended regular expressions.We can use the following grep expression: grep -Ew 'sparrow|dogs' animal-count Let’s say we want to search this file for these two phrases: To start with, we have a file called “animal-count” with the following contents: However, we can use regular expressions easily with the “-E” parameter. Normally, you’d have to use a separate grep expression for each of these phrases. You want to check the log files for the existence of some keywords that span a variety of sources. However, let’s say you have an error log file and are performing routine maintenance. Where ‘pattern’ is any given pattern or regular expression to match. Normally, the usage for grep goes something like this: grep 'pattern' filename Searching for Multiple Words at the Same Time Searching an Entire Directory for a Match and Showing the File Name.Searching for Multiple Words at the Same Time.In the second example, we used multiple grep commands and pipes to match lines containing both “dfff” and “apple” words in the file test6.txt. ➜ grep -n -w -e 'dfff' -e 'apple' test6.txt In the first example, we use the grep -e option to match the line containing the word “dfff” or “apple” in the file test6.txt. * Match file containing keyword1 or containing keyword2 … : OR * Match file containing keyword1 and containing keyword2 … : AND

But matching multiple keywords has two meanings:

Grep matches multiple keywords, which we often use on a daily basis. Sometimes, however, we also need to count the keyword to appear in the file, at the same time, according to the line number in reverse order. In the example above, we can count the number of lines or the total number of occurrences of a keyword in a file. In the following example, the grep directory contains files whose filenames contain the keyword “test”, and we use the ls command, pipe, and wc command to count the number of files whose filenames contain the keyword “test” in the directory. Grep count the number of files in the directory whose filename contains the specified keyword w, -word-regexp The expression is searched for as a word (as if surrounded by `]' see re_format(7)). o, -only-matching Prints only the matching part of the lines. In the following example, we use grep -w to count the number of times of the string “dfff” in the file ➜ grep -o -w 'dfff' test6.txt | wc -l Options: Grep counts the number of times of the specified content in a file You can also use the grep command, pipe, and wc command to achieve the same effect as the grep-c option in the following example. Using grep -c options alone will count the number of lines that contain the matching word instead of the number of total matches. In the following example, we will use the grep command to count the number of lines in the file test6.txt that contain the string “dfff” ➜ grep -c 'dfff' test6.txt Grep counts the number of lines in the file that contain the specified content

Centos grep usage