How can I avoid "no input files" error from sed, when run from xargs?
I have this shell script to update IP addresses in my configuration files (any that match $old_address_pattern must be changed to $new_address):
grep -rl "$old_address_pattern" /etc \
| xargs sed -i "s/$old_address_pattern/$new_address/g"
If the grep command finds no matching files, then sed will complain 'no input files'. How can I make this pipeline succeed when the list of files is empty?
Answer
If you want to avoid running sed when grep produces no output, then (since you've tagged this with Ubuntu), you can give the -r or --no-run-if-empty argument to xargs:
--no-run-if-empty
-r
If the standard input does not contain any nonblanks, do not run the command. Normally, the command is run once even if there is no input. This option is a GNU extension.
So your command should look like:
grep -rl "$old" /etc | xargs -r sed -i "s/$old/$new/g"