5/2/2023 0 Comments Grep usage exercises![]() With the next command, we’re piping the output from ls into grep and piping the output from grep into sort. Practically all of the lines within the log file will contain spaces, but we’re going to search for lines that have a space as their first character: grep "^ " geek-1.log The “^” regular expression operator matches the start of a line. ![]() We can force grep to only display matches that are either at the start or the end of a line. The -L (files without match) option does just that. The file names are listed, not the matching lines.Īnd of course, we can look for files that don’t contain the search term. To find out which C source code files contain references to the sl.h header file, use this command: grep -l "sl.h" *.c To see the names of the files that contain the search term, use the -l (files with match) option. grep -B 3 -x "20-Jan-06 15:24:35" geek-1.logĪnd to include lines from before and after the matching line use the -C (context) option. If you like this post, please share it on google by clicking on the +1 button.To see some lines from before the matching line, use the -B (context before) option. This can be used in grep to match the lines which end with the given string or pattern. The $ regular expression pattern specifies the end of a line. Matching the lines that end with a string This can be used in grep to match the lines which start with the given string or pattern. The ^ regular expression pattern specifies the start of a line. Matching the lines that start with a string The -b option allows the grep command to display the character position of the matched string in a file. Displaying the position of the matched string in the line We can make the grep command to display the position of the line which contains the matched string in a file using the -n option grep -n "string" file.txtġ8. We can make the grep to display only the matched string by using the -o option. grep -L "string" *īy default, grep displays the entire line which has the matched string. We can display the files which do not contain the matched string/pattern. Display the file names that do not contain the pattern. We can just display the files that contains the given string/pattern. Display the file names that matches the pattern. We can find the number of lines that matches the given string/pattern grep -c "sting" file.txtġ4. Displaying the count of number of matches. You can remove the blank lines using the grep command. You can display the lines that are not matched with the specified search sting pattern using the -v option. You can search for a string in all the files under the current directory and sub-directories with the help -r option. Searching for a sting in all files recursively This will display the matched lines and also five lines before and after the matched lines.ġ0. Displaying the lines around the match grep -C 5 "Error" file.txt This will display the matched lines along with the three lines after the matched lines.ĩ. This will prints the matched lines along with the two lines before the matched lines.Ĩ. Some times, if you are searching for an error in a log file it is always good to know the lines around the error lines to know the cause of the error. ![]() The -w option to grep makes it match only the whole words. Checking for the whole words in a file.īy default, grep matches the given string/pattern even if it found as a substring in a file. This example is just for providing the usage of regular expressions.Ħ. Regular expressions is huge topic and I am not covering it here. This will search for the lines which starts with a number. Specifying the search string as a regular expression pattern. It matches the words like “UNIX”, “Unix”, “unix”. The -i option enables to search for a string case insensitively in the give file. You can manually specify the list of files you want to search or you can specify a file pattern (use regular expressions) to search for. This is also the basic usage of the grep command. Searching for a string in multiple files. This searches for the string “Error” in the log file and prints all the lines that has the word “Error”.ģ. It searches for the given string in the specified file. This displays the last executed grep command and also prints the result set of the command on the terminal. This saves a lot of time if you are executing the same command again and again. Let see some practical examples on grep command.ġ. Grep stands for Global search for Regular Expressions and Print. You can analyze large sets of log files with the help of grep command. The power of grep comes with using its options and regular expressions. Most of us use grep just for finding the words in a file. Grep is the frequently used command in Unix (or Linux).
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