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by SEJeff 3867 days ago
or ps -ef | grep fo[o]bar

So you don't have to | grep -v grep :)

I ask people to explain what that does and how it works as a sysadmin interview question.
2 comments
notfoss 3866 days ago
That's nice. Apparently, we can place the brackets around any of the characters too! Can you explain how it works?
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SEJeff 3861 days ago
Sure, the square brackets in posix regex (used by grep) are for character ranges. You can wrap any single character in the brackets and it works the same.

So foob[a]r matches the literal string foobar. If you grepped foob[ab]r it would match both literal strings foobar and foobbr. However, it doesn't match the literal string foob[a]r because [] is a character range. To match that, you'd need to escape it something like foob\[a\]r, which would not match the literal string foobar. This is why you don't need grep -v grep

Understanding how and why this works will dramatically help you slice and dice text strings in a shell, so it makes a great SysAdmin interview question.

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nailer 3866 days ago
pgrep already excludes itself
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SEJeff 3861 days ago
Sure but that isn't often nearly as useful as something like:

ps -efH | grep foob[a]r

Where you can see the arguments and whatnot. Both are good to know.

You can use awk's ability to do posix regex and emulate pgrep with:

ps -efH | awk '/foob[a]r/{print $1}'

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