sed - apply changes in multiple files

Try:

sed -s -n -i '0,/<\/foo:bar>/p' *.txt

-s tells sed to treat each file as separate.

Because we don't want sed to quit until all the files are done, we change to just print from the beginning to <\/foo:bar> and not print the rest of the lines. -n tells sed not print unless we explicitly ask it to. The command 0,/<\/foo:bar>/p tells sed to print any line in the range from the beginning of the file to the first line that matches <\/foo:bar>.

The -s option is not available for BSD/OSX sed.

To stop reading the files when </foo:bar> is found:

With GNU awk:

gawk -i inplace '{print}; $0 == "</foo:bar>" {nextfile}' ./*.txt

With perl:

perl -ni -e 'print; close ARGV if $_ eq "</foo:bar>\n"' ./*.txt