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In your first example, you are sending the output from grep (the lines that contain 'hda') as input to next grep. So the next grep tries to find all the lines that contain 'cdrom' out of the lines that contain 'hda'. Since there are no such lines, you get no output.
Sure you can run more "pipes" in a row. Just remember that the pipe command connects the standards out to the next standard in. ie The output of
Code:
ls -al /dev | grep hda
is fed to
Code:
grep cdrom
but since the first grep only has stuff with hda in it grep will not find anything with cdrom.
use egrep and regular expressions instead.
Code:
ls -al /dev/ | egrep hda\|cdrom
performs what I think you were looking for.
the " a | b " thing is a regular expression that means " a or b". But since "|" is the pipe command you have to throw in the "\" to tell your shell that it is the "|" character and not the pipe command.
Originally posted by GŠutama Sure you can run more "pipes" in a row. Just remember that the pipe command connects the standards out to the next standard in. ie The output of
Code:
ls -al /dev | grep hda
is fed to
Code:
grep cdrom
but since the first grep only has stuff with hda in it grep will not find anything with cdrom.
use egrep and regular expressions instead.
Code:
ls -al /dev/ | egrep hda\|cdrom
performs what I think you were looking for.
the " a | b " thing is a regular expression that means " a or b". But since "|" is the pipe command you have to throw in the "\" to tell your shell that it is the "|" character and not the pipe command.
Hope it helped.
Hi,
Thanks for your advice.
That is the command I am looking for.
Previously I made a mistake. I thought it will printout what is grep one by one.
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