Question

sed ‘s_((checksum|compressed)=\”).*(\”)_\1\2_’ -i filename

I am using this command to replace the checksum and compressed filed with empty? But it didn’t change anything?

for example, I want change this line ” checksum=”XXXXX” with checksum=””, and also replace
compressed=”XXXX” with compressed=””

What is wrong with my sed command?

Answer 1

It’s because sed uses a funny regex dialect by default: you have to escape capturing brackets.
If you want to use “normal” regex that you’re familiar with, use the -r flag (if you’re on unix, GNU sed) or the -E flag (Mac OS X BSD sed):

sed -r 's_((checksum|compressed)=\").*(\")_\1\3_' -i filename

Additionally, note that you have three sets of capturing brackets in your sed, and I think you want to change the \1\2 to \1\3. (\1 contains checksum=", \2 contains checksum, and \3 contains ").

(For interest, here’s how you would do it without the extended-regexp (-r/-E) flag, note that capturing brackets and the OR | are only considered in the regex sense if they are escaped:

sed 's_\(\(checksum\|compressed\)=\"\).*\(\"\)_\1\3_' -i filename

)