My daughter is learning to count... Amelia: "1", "2", "3", "4", "5", "6", "7", pauses, "10". Me: "Most people put 8 and 9 after 7, but if you want to learn octal we can learn that too". Amelia: "No daddy I only want to count in octal".
@cuonglm find's -name matches against the basename. For / with busybox or heirloom, it seems the basename is the empty string, while it should probably be / (GNU find will give that warning if you use -name / but will still match). For a/ the basename is '' for heirloom, a/ for busybox. For a//, it's still '' for heirloom but / for busybox. Just bugs. Those implementations have simply not considered those corner cases.
@cuonglm matching / in a file name is a bug in busybox find
busybox is meant for small systems, so it's unsurprising that it has a few bugs in corner cases
GNU find treats / as the basename of the root directory (so find / -name \? matches the root directory). That's a bug, less excusable.
POSIX is buggy too (as of susv4): it defines “basename” as “The final, or only, filename in a pathname”, but the pathname / does not have any filename at all (the pathname / is decomposed as a beginning slash followed by zero filenames).
So according to these definitions / does not have a basename. But a lot of text in the spec assumes that all pathnames have a basename.
A basename is a filename, and a filename consists of 1 or more bytes that aren't /. That doesn't leave room for anything sensible for the root directory when it's expressed as / (or /// etc.).
I guess . would make sense. The basename of /. is ., and /. is the same file as /.
But it would mean that find / -name . should match the root directory, which I suspect no find implementation does, and probably other similar consequences.
> If the string pointed to by path consists entirely of the '/' character, basename() shall return a pointer to the string "/". If the string pointed to by path is exactly "//", it is implementation-defined whether '/' or "//" is returned.
Read http://pubs.opengroup.org/onlinepubs/9699919799/utilities/find.html, the 10th example, the doc said > because trailing <slash> characters are ignored when computing the basename of the file under evaluation
> A sequence of bytes consisting of 1 to {NAME_MAX} bytes used to name a file. The bytes composing the name shall not contain the <NUL> or <slash> characters.
@cuonglm No. In the context of a path name, the file name will be followed by a slash.
> A sequence of bytes consisting of 1 to {NAME_MAX} bytes used to name a file. The bytes composing the name shall not contain the <NUL> or <slash> characters. In the context of a pathname, each filename shall be followed by a <slash> or a <NUL> character;
So what is the point of POSIX definition of filename when mentioned in pathname context, filename shall be followed by /
And also, the 10th example in find spec said when computing basename but not against basename
> Except for the root directory, and "//" on implementations where "//" does not refer to the root directory, no pattern given to -name will match a <slash>, because trailing <slash> characters are ignored when computing the basename of the file under evaluation. Given two empty directories named foo and bar, the following command
@cuonglm It means that when a filename is used in the context of a pathname, then and only then, the filename will have an extra trailing /. So the file/dir foo becomes foo/ when used as a pathname.
@Gilles No the basename of / is /, so find / -prune -name / should match as -name is meant to match against the basename of the file. GNU find is compliant in that it matches but gives that irrelevant warning.
@Gilles: Here the example said > Except for the root directory, and "//" on implementations where "//" does not refer to the root directory, no pattern given to -name will match a <slash>, because trailing <slash> characters are ignored when computing the basename of the file under evaluation. Given two empty directories named foo and bar, the following command:
In case of /, the pattern give to -name can match a slash
The definition of the basename utility is equivalent to the definition of the basename concept, except that the definition of the concept doesn't give a meaning to the basename of a pathname containing only slashes.
And all this simply because an OP asked what the \ in \? means. All the poor fellow needed was an explanation of escaping and instead he got two answers delving into the depths of the POSIX specs for file name expansion.
@cuonglm no, you're right, if the basename is / then ? would match it
The problem is that nowhere does it say that the basename of / is /
> The primary shall evaluate as true if the basename of the current pathname matches pattern using the pattern matching notation described in Pattern Matching Notation. The additional rules in Patterns Used for Filename Expansion do not apply as this is a matching operation, not an expansion.
The word “basename” refers to the definition of the concept, not to the basename utility.
@gilles, pubs.opengroup.org/onlinepubs/9699919799/basedefs/… has the definition of basename which is a bit vague "The final, or only, filename in a pathname" (would still not allow the basename of / to be the empty string)
The "except for / and //..." quote @cuonglm gave is clear about the intent anyway
@StéphaneChazelas yes, because the concept is in fact only used by find. The definition of pax refers to the utility, and in other places they refer to files that can't be directories or have a non-slash character in their name.
The POSIX definition of basename when it comes to / or // or ///+ is unclear to me. Now, If / has a basename, the only possible values are "/" or "". "" doesn't make sense, so it can only be "/". The basename of a/// or a/ is "a", that at least is clear
@Gilles No, parenthesis can be used to refer to either one of the punctuation marks ( or ) or to both of them. See, for example, merriam-webster.com/dictionary/parenthesis
If my interpreting is not true, then I have the same opinion with @StéphaneChazelas, the spec should be clarified the definition for basename of /, // and ///+
@cuonglm, yes I agree. I think we all agree. The intent is that -name / should match on / or /// or ////, but as specified it's unclear. As per the definition, / has no basename, so what you'd need to pass to -name so it matches on / is unspecified (even if further down in the APPLICATION USAGE section (not normative) it makes it pretty clear that -name / should match)
Looking at the latest draft, the basename definition has been clarified: _For pathnames containing at least one filename: the final, or only, filename in the pathname. For | pathnames consisting only of <slash> characters: either ’/’ or "//" if the pathname consists of | exactly two <slash> characters, and ’/’ otherwise._
I would like to know how to delete entire rows in a postgres table that contain a particular string in the title column. So if the string is:
it is a sunny day
How can I issue a command in postgres to remove this row from the table completely. For example, the following row would be deleted:
...
Yeah, true. At some point, clearly using a programming language inside a UNIX app is off-topic. Much of that because we have better places to send them—SO, etc. This question though—seems like its a moot point if its on-topic elsewhere, as its not of sufficient quality to migrate...
But I think we'd take some questions about how to (e.g.) find a sum in LibreOffice.
Questions like that one... make me sometimes wish we had a close-as-RTFM option :-(
@terdon I'm going to add an answer that seems appropriate for the site... more or less a friendly pointer to the manual.
You modify (create, delete, change) rows in a database by talking to PostgreSQL in a language known as SQL (that's where the "SQL" in it's name comes from). The PostgreSQL documentation has pretty thorough information about the particular dialect of SQL spoken by PostgreSQL, particularly in Part ...
I would like to know how to delete entire rows in a postgres table that contain a particular string in the title column. So if the string is:
it is a sunny day
How can I issue a command in postgres to remove this row from the table completely. For example, the following row would be deleted:
...
