It cannot be passed through in the argument list. Did you mean to use the --null option? Improve this answer. Using an hex viewer like xxd really helps. Instead zsh acts as 'c code', an string ends where a null exists. It's just that the NUL character, for a terminal, is a control character, the control character that does nothing for instance it's used sometimes for slowing down the flow of character on a serial line without flow control to let the terminal like tele-typewriters in the olden days do its things like return the carriage.
So it's just that the NUL character is not visible in a terminal and it's not the only one. Pipe it into hexdump -C to confirm. Peter Cordes Peter Cordes 5, 19 19 silver badges 39 39 bronze badges. While it's not possible to include 0 bytes in the list of arguments and env vars passed to the execve system call, there's nothing preventing builtin commands or shell functions from supporting them in their arguments.
Note that it's possible to pass a NUL byte in a system call, just not for those syscall arguments that are pointers to NUL terminated strings. Example: write fd, buf, 12 here the size argument 12 indicates the extent of the binary as opposed to text string.
I clarified the bit about sys calls, since your 2nd comment is probably helpful to anyone seeing this concept for the first time. I don't think zsh itself supports it because there is no safe way to support it except weird userspace trickery PaulStelian: That's exactly the point. ZSH can handle NUL internally, but the only thing you can do with such data is write it to file descriptors with echo or printf piping into something, or a here document , not put it on command lines.
Because those system calls have to work with binary data, not strings. Show 6 more comments. BUT in some cases: give a special meaning e. Please check again! However anything contained inside the quotes will be treated as a single sting.
Search Forums. Show Threads. Show Posts. Shell Programming and Scripting. Top Forums Shell Programming and Scripting replace some string by null?? Registered User. Join Date: Dec I have a string like Quote:. Join Date: Sep Yes, try it out? Code :. It's working. Are there any other commands which serve the same purpose? From the question's title, this appears to be the distinction you are trying to make, but it is unclear from the question if indeed you care or are even aware of this distinction.
Do you care about that distinction? If so test -z will not help. Add a comment. Active Oldest Votes. Improve this answer. It can be more clear for the one reading the code that you want to see if the var is empty. I would leave the string comparison for the cases in which you are comparing with a non-empty string. Join , subscribers and get a daily digest of news, geek trivia, and our feature articles.
By submitting your email, you agree to the Terms of Use and Privacy Policy. There are a set of characters the Bash shell treats in two different ways. When you type them at the shell, they act as instructions or commands and tell the shell to perform a certain function. Think of them as single-character commands. Wherever you are in the filesystem, you can use this command to go to your home directory:. You can also use this command with relative paths. A period. You see it in directory listings if you use the -a all option with ls.
You can also use the period in commands to represent the path to your current directory. For example, if you want to run a script from the current directory, you would call it like this:. This tells Bash to look in the current directory for the script. You can use this to move up one level in the directory tree. You can also use this command with relative paths—for example, if you want to go up one level in the directory tree, and then enter another directory at that level.
You can also use this technique to move quickly to a directory at the same level in the directory tree as your current one. You hop up one level, and then back down one into a different directory. One forward-slash represents the shortest possible directory path. Because everything in the Linux directory tree starts at the root directory, you can use this command to move to the root directory quickly:.
Most often, you use the hash or number sign to tell the shell what follows is a comment, and it should not act on it. You can use it in shell scripts and—less usefully—on the command line. You can also use the hash to trim a string variable and remove some text from the beginning. It retrieves the value stored in the string variable via a parameter expansion.
We can use echo to print the value of the string variable once more and check this:. Bash shell supports three wildcards, one of which is the question mark? You use wildcards to replace characters in filename templates. A filename that contains a wildcard forms a template that matches a range of filenames, rather than just one.
The question mark wildcard represents exactly one character. Consider the following filename template:. It matches the following files.
The question mark wildcard will match both letters and numbers. The question mark wildcard must match a corresponding character in the filename. You can also use the question mark to find all files with a specific number of characters in the filenames.
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