![]() So there were about 5.9 million people in Washington State in 2000. The caret '^' means that the 'P' must occur at the beginning of the line. We can grep for and count just person records like this: The first character of a record, an H or P, indicates which kind of record it is. So, recalling that this is a 1% sample, there were 8.5 million people in Washington as of the 2000 census? Nope, the census data has two kinds of records, one for households and one for persons. Nearly always we just want to count the number of lines (records), which can be done by giving the -l option to wc.Įxample - Using grep to select a subset By default, wc prints the number of lines, words, and characters in a file. The simplest command for counting things is wc, which stands for word count. ![]() well, at least once you've figured out the right question to ask, which is, perhaps, the other 90%.Įxample - Counting the size of a population The GREP is full of global regular expression, representation of global regular expression versions, which is all users. Omit it to search only the names."90% of data analysis is counting" - John Rauser The grep command in the Linux system is a powerful text search tool that can be searched using the regular expression and prints the matching lines. Omit it to show only the process ID number. ![]() For example: pgrep -af xfceĢ958 /usr/lib/x86_64-linux-gnu/xfce4/xfconf/xfconfd So, as Sergiy Kolodyazhnyy has pointed out, often neither of those ways (nor any other approach involving piping the output of ps) is really ideal and, as Nic Hartley mentioned, other ways often use pgrep. They might not even be grep commands-just commands whose names, paths, or command-line arguments contain grep. One shortcoming of those popular methods is that they'll filter out lines that contain grep even when they're not the grep command you just ran yourself. This works because is a character class that matches exactly the letter x. So another approach is to write a regular expression that matches exactly xfce but is written differently. Grep without -F treats its pattern as a regular expression rather than a fixed string. One common way to remove this distraction is to add another pipe to grep -v grep: ps x | grep xfce | grep -v grep I'm looking for information on processes that were already running when I examined what was running, not the process that's only running because of my effort to examine what is running. My grep command was shown in the output, but it's not what I'm looking for. For example, I might be looking for running programs whose names, paths, or command-line arguments suggest they're related to Xfce: ps x | grep xfceĢ958 ? S 0:00 /usr/lib/x86_64-linux-gnu/xfce4/xfconf/xfconfdģ1901 pts/1 S+ 0:00 grep -color=auto xfce Grep -v grep (or grep -v 'grep' or grep -v "grep") often appears on the right side of a pipe whose left side is a ps command. But in most cases where grep -v grep actually appears, this is no coincidence. See man grep for details.Īs far as the grep utility is itself concerned, it's unimportant that the pattern grep passed to it as an argument is the same as its name. ![]() Without -v, it would output only the lines in which grep does appear. Grep -v "grep" takes input line by line, and outputs only the lines in which grep does not appear. ![]()
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