8 ms·

Why did they remove tilde '~' as a convenient shortcut for the Home directory?

• bch 2y ago
  Tcl Improvement Proposal (TIP) 602[0]. [0] https://core.tcl-lang.org/tips/doc/trunk/tip/602.md https://core.tcl-lang.org/tips/doc/trunk/tip/602.md
  • throw0101b 2y ago
    One example from the document: > Consider the naive attempt to clean out the /tmp directory. > cd /tmp > foreach f [glob *] {file delete -force $f} > A file ~ or ~user maliciously placed in /tmp will have rather unfortunate consequences.
    • em-bee 2y ago
      i once managed to create a directory named ~ using the mirror tool written in perl. then i naively tried to remove it using "rm -r ~" and started wondering why removing an empty directory would take so long, until it dawned on me... i learned a few new habits since then. i almost never use rm -r and i avoid "*" as a glob by itself. instead i always try to qualify "*" with a path, remove files first: "rm dir/*"; and then remove the empty directory. "rmdir dir/" if i do want to use rm -r, it is with a long path. eg in order remove stuff in the current directory i may distinctly add a path: rm -r ../currentdir/*" instead of "rm -r *" related, i also usually run "rm -i", but most importantly, i disable any alias that makes "rm -i" the default, because in order to override the -i you need to use -f, but "rm -i -f" i NOT the same thing as "rm". rm has three levels of safety: "rm -i; rm; rm -f". if "rm -i" is the default the "rm" level gets disabled, because "rm -i -f" is the same as "rm -f"
      • kristopolous 2y ago
        I've long fantasized about a tool I call "expect" that safeguards against crazy stuff like that. It has a syntax of your expectations, functionally existing as a set of boundaries, and you can hook it to always run as a wrapper for some set of commands. It essentially stages the wrapped command and if none of the boundaries are violated it goes through. Otherwise it yells at you and you need to manually override it. For instance, pretend I'm ok with mv being able to clobber except in some special directory, let's call it .bitcoin or whatever. (chattr can also solve this, it's just an example). The tool can be implemented relying on things like bpf or preload Originally I wanted it as a SQL directive ... a way to safeguard a query against doing like `update table set field=value expect rows=1` where you meant to put in the where clause but instead blew away an entire column. I think this would be especially useful surfacing it in frameworks and ORMs some of which make these accidents a bit too easy.
        • danielheath 2y ago
          For sql specifically, “limit 2” is my default way to write “expect 1”; if it affects two rows, I know that I have screwed up, whereas “limit 1” can be wrong without my noticing.
          • kristopolous 2y ago
            That's not a terrible solution although expect sounds like a simple safety mechanism for feeble-minded people like me who do simple queries. I actually know postgres people. I should probably ask them
        • kragen 2y ago
          just to clarify, this has nothing to do with the "expect" that is the other major application of tcl other than tk?
          • kristopolous 2y ago
            None. I was just reminded of a good idea I never implemented
        • progmetaldev 2y ago
          When it comes to SQL, I will often write a SELECT with very explicit search (WHERE) criteria for this very reason. Then copying that statement, commenting the original, and pasting to change into an UPDATE or DELETE statement seems to be a technique that works well for me. The SELECT tells me exactly what I'm going to UPDATE or DELETE, and once I have that, changing the syntax is very minimal. In the case of an ORM, you might have to write a tool that only listens on LOCALHOST to run these statements first.
          • kristopolous 2y ago
            I always write the where first. It's kinda like thinking in RPN or postfix. I put the parts in out of order in a way that prioritizes the minimization of error. But this is stupid. These are computers, we can make whatever we want. Executing a delete or update should, if one desires, not have to be database knifeplay.
      • sweeter 2y ago
        I love zsh auto completion for this stuff. It automatically escapes really messed up paths like paths with new lines or emojis and crazy characters like that. Its really rare but I still intentionally practiced removing these things just so I can do it safely if it ever happens.
      • sfink 2y ago
        My main safety habit is to avoid slashless paths. Bad: rm * Okay: rm ./* rm /tmp/d/* rm */deadmeat rm d/* Then again, I commonly use dangerous things like `mv somefile{,.away}` that are easy to get wrong, so maybe don't trust my advice too much.
        • mzs 2y ago
          rm -rf "$TSTDIR"/etc is pretty dangerous when you forget to set the env var
          • sfink 2y ago
            Fair! Upvoted. I guess I'm not likely to type that into the shell, or if I do, I then tab-complete to expand it. I could definitely see myself using that in a shell script, though. I tend to do validity checks there: if ! [ -d "$TSTDIR" ]; echo "$TSTDIR not found, stupid" >&2; exit 1; fi but that's kind of irrelevant, since if I need it to exist then I won't be removing it. Plus, I could totally see myself doing if [ -d "$TESTDIR" ]; then rm -rf "$TSTDIR"/etc fi
          • oneshtein 2y ago
            In bash, `set -u` or `"${TSTDIR:?Error: TSTSDIR is required.}/etc"` protects from such errors.
        • niobe 2y ago
          My safety technique is to echo the commands before I do the actual commands as a sanity check, e.g. for i in $(find something); do echo "rm -f $i"; done (bash example as my TCL is rusty)
          • dundarious 2y ago
            Change your do block to `printf %q\ rm -f "$i" ; echo` and it won't lie about spaces. In case HN has "trimmed" my post in some way, as it often does, that's: percent q backslash space space. Works in bash/zsh, but not dash, probably not whatever your sh is. Can make a function of it trivially, but you have to handle the $# -eq 0 case, return whatever printf returns, etc.
      • progmetaldev 2y ago
        Very cool of you to post this. Too many people won't post stories like this, but I've done very similar multiple times. I think it definitely helps reinforce proper habits, and is the best way to cut your teeth on technology. It's also great for anyone new to read something like this, and be able to avoid something so devastating, and maybe make lesser mistakes, but still learn from both!
        • em-bee 2y ago
          when you get to be as old as i am, these are the war stories you share with your kids and grandkids around the campfire ;-) like the one from my colleague who once fat fingered fsck into mkfs and i lost my personal homepage because of it. what makes me uncomfortable about that story is that it was not my fault. if it were it would have been easier to tell. but at the time i was quite frustrated and my colleague felt that despite me trying to not get angry at him. i still feel really bad about my reaction then, adding to his predicament, since he had to live with the guilt about losing our website and everyone's personal home directory. it's bad when a mistake causes you to loose something personal, but so much worse when you loose someone elses stuff. talking about mistakes is how we learn from them. the important part is not to get embarrassed about them. however that requires an environment where we are not blaming each other when something goes wrong. i could have made that mistake myself. and i applied this lesson to my own learning as if i had. blessed be the pessimist, for he hath made backups...
          • progmetaldev 2y ago
            Absolutely, the worst mistakes are the biggest opportunities for learning. Destroying your own files is painful. Destroying EVERYONE'S files is a lesson that is more painful and something you will be more careful not to repeat. I try to tell as many of these stories in person as possible, to let everyone know that unless you have dealt with this kind of accident, you're either in the 1% or due for your turn. I'd like to think that sharing these stories might at least give someone some pause before they go ahead and throw caution to the wind.
      • barosl 2y ago
        > if "rm -i" is the default the "rm" level gets disabled, because "rm -i -f" is the same as "rm -f" You can use "\rm" to invoke the non-aliased version of the command. I made "rm -i" the default using an alias and occasionally use "\rm" to get the decreased safety level you described. I think it is more convenient that way.
      • rixed 2y ago
        You could also create a file named "-i" in your home dir.
      • somat 2y ago
        When deleting, if it is more than a few specifically named files I will use a "find ... -delete" invocation. I like it for two reasons. Find feels like it has more solidly defined patterns and recursion than shell globing and by leaving off the "-delete" it give me a chance to inspect the results before committing to my actions.
        • kstrauser 2y ago
          Without testing, I wonder if find follows symlinks. I’m pretty sure rm doesn’t. Edit: Just checked and find doesn’t by default.
      • cassepipe 2y ago
        Why not learn to enjoy life knowing you get a second chance instead ?: https://github.com/rushsteve1/trash-d https://github.com/rushsteve1/trash-d
        • em-bee 2y ago
          because then i become to rely on stuff being in the trash and i'd be less careful when deleting, which means i have to double check when i clean the trash. that's extra work. . and since the trash is one single folder for the whole desktop, that means the trash is full of stuff from all over the place, making a review extra hard. in most cases i know something needs to be gone, so i'd rather delete it on the spot. besides that, the primary reason for deleting stuff is to gain space. moving things to trash doesn't help with that. what i sometimes do though, when mass deleting, is to move stuff to be deleted into a new folder (usually called "del" or "delete"). then verify the contents of the folder before removing it. what would be more useful is a kind of trash implementation that does not take space, in that it keeps files around but reports them as unused space that can be overwritten when space is needed. kind of like undelete is possible on some filesystems. so that gone is gone because i can't control when deleted space gets used up, but in a panic situation i can revert the most recent deletes.
    • AlienRobot 2y ago
      I once created a file named *. Sweats were sweated that day.
      • orthoxerox 2y ago
        I've heard that one of the Unix founding fathers had a directory with 125 files that all had single-byte names: one for each ASCII symbol except slash, dot and null. He would then test any new utility against this directory and chew the careless programmer out if it couldn't correctly handle every one of these names.
    • amelius 2y ago
      Isn't that just tilde-expansion happening at the wrong moment?
• cmacleod4 2y ago
  In the long run, special cases like that often turn out to be more trouble than they are worth. If an ordinary file happened to start with '~' it would not be handled correctly. So you either accept or ignore that potential problem, or you have to write extra code to work around it. It's safer to not have such special cases at all.
  • mirekrusin 2y ago
    Should be starts with ~/
    • cmacleod4 2y ago
      No, ~abc will be interpreted as the home directory of user abc in Tcl 8.*
      • eviks 2y ago
        Then you fix this mistake, not remove ~ completely
        • Y_Y 2y ago
          It's not a mistake
          • mirekrusin 2y ago
            If it's not a mistake then why they took it off?
            • cmacleod4 2y ago
              The original design decision was to behave like a shell, where ~ means your own home dir and ~fred means fred's home dir. With the benefit of experience, this is now seen to be unwise and a different decision has been made.
• Koshkin 2y ago
  Just recently I used '~' in the remote target path in the scp command, and, somewhat unexpectedly, it created the directory with that name and put the files there.
• isr 2y ago
  In 99% of cases, yes - this is a pain in the backside. Long ago I adopted something from the plan9 way of doing things (when I was heavily using acme). Just symlink /h to /home. So ~user becomes /h/user, in places where ~ is not expanded for you.