Extract substring according to regexp with sed or grep

grepregular expressionsed

In a (BSD) UNIX environment, I would like to capture a specific substring using a regular expression.

Assume that the dmesg command output would include the following line: 

pass2: <Marvell Console 1.01> Removable Processor SCSI device

I would like to capture the text between the < and > characters, like

dmesg | <sed command>

should output:

Marvell Console 1.01

However, it should not output anything if the regex does not match. Many solutions including sed -e 's/$regex/\1/ will output the whole input if no match is found, which is not what i want.

The corresponding regexp could be:
regex="^pass2\: \<(.*)\>"

How would i properly do a regex match using sed or grep? Note that the grep -P option is unavailable in my BSD UNIX distribution. The sed -E option is available, however.

Best Answer

Try this,

sed -nE 's/^pass2:.*<(.*)>.*$/\1/p'

Or POSIXly (-E has not made it to the POSIX standard yet as of 2019):

sed -n 's/^pass2:.*<\(.*\)>.*$/\1/p'

Output:

$ printf '%s\n' 'pass2: <Marvell Console 1.01> Removable Processor SCSI device' | sed -nE 's/^pass2:.*<(.*)>.*$/\1/p'
Marvell Console 1.01

This will only print the last occurrence of <...> for each line.

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