Using output of previous commands in bash

Question

In Mathematica, it is possible to reuse the output of the previous command by using %.

Is something similar possible for bash (or some other shell)?

For example, I run a make which gives warnings, but I want to find all warnings. So, I type

make | grep "warning"

but I'm not able to see the output of the make then.

I would like to type something like this instead:

make
% | grep "warning"

Answer 1

Since the amount of output is indeterminate, it doesn't make sense for bash to store it for you for re-display. But there's an alternate solution to your problem:

The tee command allows you to duplicate an output stream to a file. So if you're willing to use a file for temporary storage, you can do something like this:

make | tee output.txt
grep "warning" output.txt

This solution avoids running make twice, which could be (a) expensive and (b) inconsistent: the second make may be doing less work than the first because some targets were already made the first time around.

Note: I haven't tried this. You may need to fiddle with joining the error and output streams, or such.

Answer 2

I'm not sure if the make command sends warnings to stderr but I suspect it does. try this

make 2&>1 |grep 'warning'

it will redirect stderr to stdout.

Should also note that you can't grep anything that's not going to stdout.

Answer 3

If you use tee to duplicate the output stream to /dev/stderr, there's no need for a temp file; plus, after that, you can filter the stdout stream with sed to create a make_warning.log file - all in one line of Unix shell pipes.

make 2>&1 | tee /dev/stderr | \
   sed -E -n 's/(.*[Ww][Aa][Rr][Nn][Ii][Nn][Gg].*)/\1/p' > make_warning.log

Answer 4

# swap stdout and stderr stream to log entire stderr stream
make 3>&2 2>&1 1>&3 3>&- | tee /dev/stderr > stderr.log