How do I grep an old line?
To also show you the lines before your matches, you can add -B to your grep. The -B 4 tells grep to also show the 4 lines before the match. Alternatively, to show the log lines that match after the keyword, use the -A parameter. In this example, it will tell grep to also show the 2 lines after the match.
Which of the grep command option will select non matching lines from given file?
The grep Command
| Options | Meaning |
|---|---|
| -o, –only-matching | Print only the matched (non-empty) parts of a matching line, with each such part on a separate output line. |
| -v, –invert-match | Invert the sense of matching, to select non-matching lines. |
Is there a way to grep a stream?
Yes, this will actually work just fine. Grep and most Unix commands operate on streams one line at a time. Each line that comes out of tail will be analyzed and passed on if it matches. you can check by type alias if this outputs something like tail isan alias of colortail -n 30 . then you have your culprit 🙂
How to remove a line feed from grep?
The normal version of grep (including grep -P) always outputs a line feed with its match, so if you only have one result (or you only want the final added line feed to be removed), it suffices to simply remove the final character of the output, which you can do by piping it through head -c-1.
How to make grep output without trailing newline?
The “ or $ () will remove the newline from the end, but to do this programatically, use tr. This will remove the carriage return and/or the newline from the string. What might be the problem is how you then output the result. For example, by default, echo adds a newline.
Is it true that grep does not use output buffering?
Tail doesn’t use output buffering – grep does. No, grep does not do output buffering when the output is going to a tty device, as it clearly is in this answer. It does line buffering! This is the correct answer and should be the accepted answer.