how to use xargs with sed in search pattern

Question

I need to use the output of a command as a search pattern in sed. I will make an example using echo, but assume that can be a more complicated command:

echo          


        

Answer 1

This might work for you (GNU sed):

echo "some pattern" | sed 's|.*|s/&/replacement/g|' | sed -f - -i file.txt

Essentially turn the some pattern into a sed substitution command and feed it via a pipe to another sed invocation. The last sed invocation uses the -f switch which accepts the sed commands via a file, the file in this case being the standard input -.

If you are using bash, the here-string can be employed:

<<<"some pattern" sed 's|.*|s/&/replacement/g|' | sed -f - -i file.txt

N.B. the sed separators | and / should not be a part of some pattern otherwise the regexp will not be formed properly.