5 ms·

My addendums: tail -f # -f follows live files. Very useful for watching log files from /var/log in real time grep -Iir “pattern” * # search local and subdir

My addendums: tail -f # -f follows live files. Very useful for watching log files from /var/log in real time grep -Iir “pattern” * # search local and subdirectories for pattern, skip binary files, case insensitive. Handy for searching whole source trees tail -f file | grep “pattern” # useful for live watching very busy logs where you know a specific pattern you’re looking for find . | grep “filenamepattern” # search the local directory and down for filenames matching a pattern. Find actually has arguments for doing the search itself, but I know grep already. For more structured types of searches “e.g. I want to find a file named that is of a particular type”, man find

assbuttbuttass 5y ago
I used to use find and grep together but find is really so easy to use by itself: find . -name 'filenamepattern' The only difference is it's a glob, not a regex.
dspillett 5y ago
To extend a little: > tail -f Or tail -f filename-to-watch if looking at a file that might be renamed and stop updating (i.e. log files that are rotated). Without a filename the file descriptor is followed so when for instance access.log becomes access.log.1 your display keeps following access.log.1 not the new access.log which is probably what you want. > find . | grep I add “-type f” to find's params when doing that, as I'm almost invariably doing something that I don't want to apply to sub-directories (just the files within them). Also if sending the file list to grep for searching the contents not the names: find . -type f -print0 | xargs -0 grep options-and-stuff-to-find which deals with the common issue of spaces in filenames. Or you can do find . -type f -exec grep stuff-to-find {} \; to avoid the extra invocation of xargs, but I consider this less beginner-friendly (you have to remember the “;” and that it usually needs to be escaped or the shell will take it as an end of statement marker and not pass it to find, the error message “missing argument to `-exec'” received when you forget it not particularly helpful IMO if you don't know _or_ temporarily draw a mental blank).
- thestoicattack 5y ago
  As a note, find . -type f -exec grep stuff {} \; will also invoke a new grep process for every file, which can be slow. If you think find is going to return a lot of files, it is often better to use find . -type f -exec grep stuff {} + # note plus sign which will replace {} with as many filenames as allowed (all correctly quoted, etc).
  - dspillett 5y ago
    Ah, yes, the other reason not to use that form: remembering to use + instead of ; for efficiency! No point removing xargs just to add in many more invocations of the target command.
- martinflack 5y ago
  > if looking at a file that might be renamed and stop updating (i.e. log files that are rotated). Without a filename the file descriptor is followed so when for instance access.log becomes access.log.1 your display keeps following access.log.1 not the new access.log which is probably what you want. I believe that's true if you name a file as well (just tested it on Ubuntu). You keep following the original file you named, even if it becomes renamed; you don't follow a new file by the same name. Using something like "watch -n5 tail filename" polls every few seconds to show the bottom of a file, and goes for the current file at that filename each time.
  - Arnavion 5y ago
    `tail -F` is what you're looking for. No need to implement it manually with `watch`.
    - martinflack 5y ago
      TIL! Thanks
  - dspillett 5y ago
    Ah, checking the man-page it would seem that you need to use the long-form option for the behaviour I described to work: tail --follow=file-to-follow-by-name > watch -n5 tail filename That works too, and for many other uses, but doesn't allow scroll-back which can be significant when a lot of information comes through at once.
traceroute66 5y ago
Really fgrep (or grep -F) should be used if there's no need for grep magic.

assbuttbuttass 5y ago

I used to use find and grep together but find is really so easy to use by itself: find . -name 'filenamepattern' The only difference is it's a glob, not a regex.

dspillett 5y ago

To extend a little: > tail -f Or tail -f filename-to-watch if looking at a file that might be renamed and stop updating (i.e. log files that are rotated). Without a filename the file descriptor is followed so when for instance access.log becomes access.log.1 your display keeps following access.log.1 not the new access.log which is probably what you want. > find . | grep I add “-type f” to find's params when doing that, as I'm almost invariably doing something that I don't want to apply to sub-directories (just the files within them). Also if sending the file list to grep for searching the contents not the names: find . -type f -print0 | xargs -0 grep options-and-stuff-to-find which deals with the common issue of spaces in filenames. Or you can do find . -type f -exec grep stuff-to-find {} \; to avoid the extra invocation of xargs, but I consider this less beginner-friendly (you have to remember the “;” and that it usually needs to be escaped or the shell will take it as an end of statement marker and not pass it to find, the error message “missing argument to `-exec'” received when you forget it not particularly helpful IMO if you don't know _or_ temporarily draw a mental blank).

thestoicattack 5y ago
As a note, find . -type f -exec grep stuff {} \; will also invoke a new grep process for every file, which can be slow. If you think find is going to return a lot of files, it is often better to use find . -type f -exec grep stuff {} + # note plus sign which will replace {} with as many filenames as allowed (all correctly quoted, etc).
- dspillett 5y ago
  Ah, yes, the other reason not to use that form: remembering to use + instead of ; for efficiency! No point removing xargs just to add in many more invocations of the target command.
martinflack 5y ago
> if looking at a file that might be renamed and stop updating (i.e. log files that are rotated). Without a filename the file descriptor is followed so when for instance access.log becomes access.log.1 your display keeps following access.log.1 not the new access.log which is probably what you want. I believe that's true if you name a file as well (just tested it on Ubuntu). You keep following the original file you named, even if it becomes renamed; you don't follow a new file by the same name. Using something like "watch -n5 tail filename" polls every few seconds to show the bottom of a file, and goes for the current file at that filename each time.
- Arnavion 5y ago
  `tail -F` is what you're looking for. No need to implement it manually with `watch`.
  - martinflack 5y ago
    TIL! Thanks
- dspillett 5y ago
  Ah, checking the man-page it would seem that you need to use the long-form option for the behaviour I described to work: tail --follow=file-to-follow-by-name > watch -n5 tail filename That works too, and for many other uses, but doesn't allow scroll-back which can be significant when a lot of information comes through at once.

traceroute66 5y ago

Really fgrep (or grep -F) should be used if there's no need for grep magic.