I am not able to find out if and how it is possible to make a dry run with sed.
So i have this command:
find ./ -type f | xargs sed -i 's/string1/string2/g'
But before I really substitute in all the files, i want to check what it WOULD substitute. Copying the whole directory structure to check is no option!
Thanks for any feedback (negative or positive :) )
Remove the -i and pipe it to less to paginate though the results. Alternatively, you can redirect the whole thing to one large file by removing the -i and appending > dryrun.out
I should note that this script of yours will fail miserably with files that contain spaces in their name or other nefarious characters like newlines or whatnot. A better way to do it would be:
while IFS= read -r -d $'\0' file; do
sed -i 's/string1/string2/g' "$file"
done < <(find ./ -type f -print0)
I would prefer to use the p-option:
find ./ -type f | xargs sed 's/string1/string2/gp'
Could be combined with the --quiet parameter for less verbose output:
find ./ -type f | xargs sed --quiet 's/string1/string2/gp'
From man sed:
p:
Print the current pattern space.
--quiet:
suppress automatic printing of pattern space
I know this is a very old thread and the OP doesn't really need this answer, but I came here looking for a dry run mode myself, so thought of adding the below piece of advice for anyone coming here in future. What I wanted to do was to avoid stomping the backup file unless there is something really changing. If you blindly run sed using the -i option with backup suffix, existing backup file gets overwritten, even when there is nothing substituted.
The way I ended up doing is to pipe sed output to diff and see if anything changed and then rerun sed with in-place update option, something like this:
if ! sed -e 's/string1/string2/g' $fpath | diff -q $fpath - > /dev/null 2>&1; then
sed -i.bak -e 's/string1/string2/g' $fpath
fi
As per OP's question, if the requirement is to just see what would change, then instead of running the in-pace sed, you could do the diff again with some informative messages:
if ! sed -e 's/string1/string2/g' $fpath | diff -q $fpath - > /dev/null 2>&1; then
echo "File $fpath will change with the below diff:"
sed -e 's/string1/string2/g' $fpath | diff $fpath -
fi
You could also capture the output in a variable to avoid doing it twice:
diff=$(sed -e 's/string1/string2/g' $fpath | diff $fpath -)
if [[ $? -ne 0 ]]; then
echo "File $fpath will change with the below diff:"
echo "$diff"
fi
