![]() ![]() ![]() Now you have two processes running, the first grep and the shell, and they are both trying to read from the keyboard, and it is not determinate which one gets any given line of input (or any given EOF indication). With Heirloom Shell, the second grep completes and exits, and the shell prompts again. With Bash, the parent shell waits until all the processes in the pipeline have exited, so it sits around waiting for the grep -c to finish, which it won't do until you indicate EOF. Note that the second grep doesn't read its standard input at all, so the pipe is superfluous. Or, in my case, it will fail since there's neither a file nor a directory called logs where I'm running the pipeline. The second grep does a recursive search for 'word2' in the files underneath directory logs (or, if it is a file, in the file logs). by typing Control-D), it will sit there, waiting for you to type something. The first grep is going to count the number of occurrences of 'word1' on its standard input, and print that number on its standard output. The initial script is: grep -c "word1" | grep -r "word2" logs If you run two commands, you should aim to select the less frequently occurring word in the first grep to minimize the amount of data processed by the second. Against that, the regex is more complex you might need to benchmark it to find out what's best - but only if performance really matters. However, if the file is huge and 'word1' occurs frequently, then you may be passing significant data down the pipe where a single command avoids that overhead. If the file is big but only a few lines contain 'word1', there isn't going to be much data passed on the pipe and using two command is fine. If the file is small, performance isn't likely to be an issue and running two commands is fine. How much this matters depends on how big the data file is and how many lines match 'word1'. The 'one command' variants have the advantage that there is only one process running, and so the lines containing 'word1' do not have to be passed via a pipe to the second process. If you know that 'word1' will precede 'word2' on the line, you don't even need the alternatives and regular grep would do: grep 'word1.*word2' logs You could use extended grep ( grep -E or egrep): grep -E 'word1.*word2|word2.*word1' logs However, it isn't necessary to use two commands like that. The first grep finds lines with 'word1' from the file 'logs' and then feeds those into the second grep which looks for lines containing 'word2'. The –v option tells grep to invert its output, meaning that instead of printing matching lines, do the opposite and print all of the lines that don’t match the expression.One simple rewrite of the command in the question is: grep "word1" logs | grep "word2" The -v option instructs grep to print all lines that do not contain or match the expression. ![]() You can append as many filenames as needed. The terminal prints the name of every file that contains the matching lines, and the actual lines that include the required string of characters. ![]() To search multiple files with the grep command, insert the filenames you want to search, separated with a space character. How do I grep a word in multiple files in Linux? To interpret the pattern as an extended regular expression, use the -E ( or –extended-regexp ) option. In its simplest form, when no regular expression type is given, grep interpret search patterns as basic regular expressions. GNU grep supports three regular expression syntaxes, Basic, Extended, and Perl-compatible. In this example, it will tell grep to also show the 2 lines after the match. Alternatively, to show the log lines that match after the keyword, use the -A parameter. The -B 4 tells grep to also show the 4 lines before the match. To also show you the lines before your matches, you can add -B to your grep. How do you grep multiple lines after a match? The first two grep commands print just the line with the match and the last one prints the line and one line after. Use a single arrow the first time and double arrows subsequent times to append to the file. The tool prints all lines that contain the words you specify as a search pattern. You can grep multiple strings in different files and directories. What is grep command? Can you grep for multiple patterns in a file?īy using the grep command, you can customize how the tool searches for a pattern or multiple patterns in this case.What options can be used with grep command?.How do you get 10 lines before and after grep?.How do I grep a word in multiple files in Linux?.How do you find a pattern in all files in UNIX using grep?.How do you grep multiple lines after a match?.Can you grep for multiple patterns in a file?. ![]()
0 Comments
Leave a Reply. |
AuthorWrite something about yourself. No need to be fancy, just an overview. ArchivesCategories |