grep -v "grep" takes input line by line, and outputs only the lines in which grep does not appear. Without -v, it would output only the lines in which grepdoes appear. See man grep for details.
As 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. But in most cases where grep -v grep actually appears, this is no coincidence.
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. That is likely where you have seen it. For example, I might be looking for running programs whose names, paths, or command-line arguments suggest they're related to Xfce:
My grep command was shown in the output, but it's not what I'm looking for. 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.
One common way to remove this distraction is to add another pipe to grep -v grep:
ek@Io:~$ ps x | grep xfce | grep -v grep
2955 ? Ssl 0:10 xfce4-power-manager
2958 ? S 0:00 /usr/lib/x86_64-linux-gnu/xfce4/xfconf/xfconfd
grep without -F treats its pattern as a regular expression rather than a fixed string. So another approach is to write a regular expression that matches exactly xfce but is written differently. For example:
ek@Io:~$ ps x | grep '[x]fce'
2955 ? Ssl 0:10 xfce4-power-manager
2958 ? S 0:00 /usr/lib/x86_64-linux-gnu/xfce4/xfconf/xfconfd
This works because [x] is a character class that matches exactly the letter x.
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. They might not even be grep commands--just commands whose names, paths, or command-line arguments containgrep. 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, otherways often use pgrep. For example:
You can use -v flag to print inverts the match; that is, it matches only those lines that do not contain the given word. For example print all line that do not contain the word bar:
grep -v "grep"takes input line by line, and outputs only the lines in whichgrepdoes not appear. Without-v, it would output only the lines in whichgrepdoes appear. Seeman grepfor details.As far as the
greputility is itself concerned, it's unimportant that the patterngreppassed to it as an argument is the same as its name. But in most cases wheregrep -v grepactually appears, this is no coincidence.grep -v grep(orgrep -v 'grep'orgrep -v "grep") often appears on the right side of a pipe whose left side is apscommand. That is likely where you have seen it. For example, I might be looking for running programs whose names, paths, or command-line arguments suggest they're related to Xfce:My
grepcommand was shown in the output, but it's not what I'm looking for. 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.One common way to remove this distraction is to add another pipe to
grep -v grep:grepwithout-Ftreats its pattern as a regular expression rather than a fixed string. So another approach is to write a regular expression that matches exactlyxfcebut is written differently. For example:This works because
[x]is a character class that matches exactly the letterx.One shortcoming of those popular methods is that they'll filter out lines that contain
grepeven when they're not thegrepcommand you just ran yourself. They might not even begrepcommands--just commands whose names, paths, or command-line arguments containgrep. So, as Sergiy Kolodyazhnyy has pointed out, often neither of those ways (nor any other approach involving piping the output ofps) is really ideal and, as Nic Hartley mentioned, other ways often usepgrep. For example:-ashows the full command line. Omit it to show only the process ID number.-fsearches in full command line. Omit it to search only the names.grep --helptells us what-vflag does:You can use
-vflag to print inverts the match; that is, it matches only those lines that do not contain the given word. For example print all line that do not contain the word bar:(read more...)