如何找到目录中最新修改文件的时间戳（递归）？

Question

I'm working on a process that needs to be restarted upon any change to any file in a specified directory, recursively.

I want to avoid using anything heavy, like inotify . I don't need to know which files were updated, but rather only whether or not files were updated at all. Moreover, I don't need to be notified of every change, but rather only to know if any changes have happened at a specific interval, dynamically determined by the process.

There has to be a way to do this with a fairly simple bash command. I don't mind having to execute the command multiple times; performance is not my primary concern for this use case. However, it would be preferable for the command to be as fast as possible.

The only output I need is the timestamp of the last change, so I can compare it to the timestamp that I have stored in memory.

I'm also open to better solutions.

Answer 1

I actually found a good answer from another closely related question .

I've only modified the command a little to adapt it to my needs:

find . -type f -printf '%T@\\n' | sort -n | tail -1

1. %T@ returns the modification time as a unix timestamp, which is just what I need.
2. sort -n sorts the timestamps numerically.
3. tail -1 only keeps the last/highest timestamp.

It runs fairly quickly; ~400ms on my entire home directory, and ~30ms on the intended directory (measured using time [command] ).

Answer 2

I just thought of an even better solution than the previous one , which also allows me to know about deleted files.

The idea is to use a checksum, but not a checksum of all files; rather, we can only do a checksum of the timestamps. If anything changes at all (new files, deleted files, modified files), then the checksum will change also!

find . -type f -printf '%T@,' | cksum

1. '%T@,' returns the modification time of each file as a unix timestamp, all on the same line.
2. cksum calculates the checksum of the timestamps.
3. ????
4. Profit!!!!

It's actually even faster than the previous solution (by ~20%), because we don't need to sort (which is one of the slowest operations). Even a checksum will be much faster, especially on such a small amount of data (22 bytes per timestamp), instead of doing a checksum on each file.

Answer 3

Instead of remembering the timestamp of the last change, you could remember the last file that changed and find newer files using

find . -type f -newer "$lastfilethatchanged"

This does not work, however, if the same file changes again. Thus, you might need to create a temporary file with touch first:

touch --date="$previoustimestamp" "$tempfile"
find . -type f -newer "$tempfile"

where "$tempfile" could be, for example, in the memory at /dev/shm/ .

Answer 4

$ find ./ -name "*.sqlite" -ls 在这里您可以使用此命令获取文件信息。使用过滤器获取时间戳