![]() ![]() Keep up the good work, we all tend to just sit with what we know and are comfortable with, good to get new ideas. The big upside of grep is its readability compared to sed/awk/perl, even if it is at the cost of power. and called these instead of grep in my script. I wrote a number of C++ functions which took an input file, output file and search pattern as arguments, slightly differing dependent upon whether inclusive or exclusive searches were required etc. I looked at top and found that the script which is run every 3 minutes, was taking nearly 2 minutes to complete. The scripts were to utilise the iptables and ipset firewall setup, by analysing the apache logs for malicious scans, POSTs etc.Īnd adding the offending IP to an ipset which determined future access. Grep is fine for one off or irregular searches, but its limitations were brought home to me when I scripted firewall scripts using it for my server. Posted in Hackaday Columns, Linux Hacks, Slider Tagged grep, linux, regular expression, ripgrep, rust Post navigation ![]() If you want a fun way to learn regular expressions, try a crossword puzzle. Of course, to get the most out of any grep-like tool, you really need to know regular expressions. This is one of those simple tools that you can certainly live without, but it is much nicer to do many common tasks with it than without it. You can match across lines, match binary files, use CRLF as a line terminator, show context lines, or filter each file through an external program. This causes the search expression to be an ordinary string: If you have trouble quoting regular expressions when you just want to find some text, you’ll appreciate the -F option. With the PCRE2 engine you can do look-around, backreferences, and more. If you provide multiple expressions, they will all use the same expression engine, so any PCRE2 expression will force the use of that engine. This will cause rg to use Rust expressions unless you appear to use features that require PCRE2. You can use the -P option to select PCRE2 regular expressions which have more features but might be slower. These are known to be fast, but have some limitations in the name of performance. Rg -passthrough 'Jen' -r 'Jennifer' invite.txt | sponge invite.txtīy default, rg uses regular expressions from Rust. So to make a replacement in a file you could use something like: Sponge copies its standard input to a file, but it waits until there is no more input before it does so. A utility called sponge is a neater way to do it. Of course, you can send the output to a temporary file and then replace the original file with the temporary one. This is a common use case for rg, though. For example, try this:Ĭat test.txt # oops, the file is now empty One of the classic problems with Linux multitasking is trying to overwrite a file. For example, -v will invert the match so that only lines that don’t match print. In that case, send the -passthru option so that all lines are sent through even if they don’t match.Ĭonversely, you might want to only print out the parts that match and not the entire line. Suppose you wanted to create a new file with the replacement, though. You can also specify a replacement with -r: If you don’t want the line numbers, use the -N option. One refreshing upgrade is that it does output line numbers when printing to stdout: If you want to use rg as a grep, go ahead. Since the whole purpose of the program is to change files, I didn’t think that was too surprising, so I did the install. It informed me that I had to add –classic to the install line because ripgrep could affect files outside the Snap sandbox. I usually hate installing a snap, but I did anyway. When I tried running KDE Neon, it helpfully told me that I could install a version using apt or take a Snap version that was newer. Your best bet is to get ripgrep from your repositories. Using rg, you can do things that grep can do using more modern regular expressions and also do replacements. ![]() That’s the idea behind ripgrep which actually has the command name rg. You could use awk, but as a general-purpose language, it seems a bit of overkill for such a simple and common task. You might use sed, but it is somewhat hard to use. Maybe you want to change each instance of “HackADay” to “Hackaday,” for example. Of course, grep is fine for looking, but what if you want to find things and change them. Even if you aren’t a regular expression guru, it is easy to use grep to search for lines in a file that match anything from simple strings to complex patterns. If you are even a casual Linux user, you probably know how to use grep.
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