So this doesn’t seem like a terribly complicated question I have, but it’s one I can’t find the answer to. I’m confused about what the -p option does in Unix. I used it for a lab assignment while creating a subdirectory and then another subdirectory within that one. It looked like this: This is in a private … Read more
You only need a minimal change; single-quote the here-document delimiter after <<. or equivalently backslash-escape it: Without quoting, the here document will undergo variable substitution, backticks will be evaluated, etc, like you discovered. If you need to expand some, but not all, values, you need to individually escape the ones you want to prevent. will produce … Read more
Real, User and Sys process time statistics One of these things is not like the other. Real refers to actual elapsed time; User and Sys refer to CPU time used only by the process. Real is wall clock time – time from start to finish of the call. This is all elapsed time including time slices used … Read more
It’s called a shebang, and tells the parent shell which interpreter should be used to execute the script. Most scripting languages tend to interpret a line starting with # as comment and will ignore the following !/usr/bin/whatever portion, which might otherwise cause a syntax error in the interpreted language.
That means that you are printing output on the main output device for the session… whatever that may be. The user’s console, a tty session, a file or who knows what. What that device may be varies depending on how the program is being run and from where. The following command will write to the … Read more
root can do everything, others (with userid != 0) can’t do anything. But anyone who has write access to the containing folder is allowed to delete the file. The owner can of course always change the flags and regain access anytime.
WEXITSTATUS(stat_val) is a macro (so in fact it does not “return” something, but “evaluates” to something). For how it works you might like to look it up in the headers (which should be #included via <sys/wait.h>) that come with the C-compiler you use. The implementation of this macro might differ from one C-implementation to the other. Please note, … Read more
Bus errors are rare nowadays on x86 and occur when your processor cannot even attempt the memory access requested, typically: using a processor instruction with an address that does not satisfy its alignment requirements. Segmentation faults occur when accessing memory which does not belong to your process. They are very common and are typically the … Read more
Unix uses 0xA for a newline character. Windows uses a combination of two characters: 0xD 0xA. 0xD is the carriage return character. ^M happens to be the way vim displays 0xD (0x0D = 13, M is the 13th letter in the English alphabet). You can remove all the ^M characters by running the following: Where ^M is entered by holding down Ctrl and … Read more
chmod a+x modifies the argument’s mode while chmod 755 sets it. Try both variants on something that has full or no permissions and you will notice the difference.