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15. Actually, `$` refer to `value of` and. `#` refer to `number of / total number`. So together. `$#` refer to `The value of the total number of command line arguments passed.`. Thus, you can use $# to check the number of arguments/parameters passed like you did and handle any unexpected situations.
It's used to evaluate code dynamically. In shells, it's implemented as a shell builtin command. Basically, eval takes a string as argument and evaluates/interprets the code in it. In shells, eval can take more than one argument, but eval just concatenates those to form the string to evaluate.
This latter usage is faster, does not contaminate the shell's variable namespace with what amounts to temp variables, can often be a lot more readable for humans and encourages the use of "positive logic", the practice of writing conditionals without negations, which has cognitive simplicity in most situations.
yes, and as I said, you're free to code your project the way you like. But, next to stating your preference to using braces, you linked to an article titled "Why You Should Put Braces around Your Variables When Shell Scripting", but TBF, I don't see much rationale for always using braces in that article.
See What is the difference between > and >> (especially as it relates to use with the cat program)?, What does “3>&1 1>&2 2>&3” do in a script? and of course, your shell's manual. (There are some further explanations in Is this a typo in Bash manual's redirection section? too.) –
Aug 17, 2012 · 341. The following command will do it for you. Use caution though if this isn't your intention as this also removes files in the directory and subdirectories. "-f" is "--force" which overrides some sanity checks and prompting. A safer command to start with would be rm -r directoryname.
You can always try the obvious things like ^C, ^D (eof), Escape etc., but if all fails I usually end up suspending the command with ^Z (Control-Z) which puts me back into the shell. I then do a ps command and note the PID (process id) of the command and then issue a kill thePID (kill -9 thePID if the former didn't work) command to terminate the ...
5. The backtick ` runs the contents of the enclosed string, so something like this. will find out the path to the hostname command, and then tell you how it was built. The command that you put in your question runs id -u to get the effective user id, and then changes the ownership of /somedir to that user.
Kernel Version. If you want kernel version information, use uname(1). For example: $ uname -a Linux localhost 3.11.0-3-generic #8-Ubuntu SMP Fri Aug 23 16:49:15 UTC 2013 x86_64 x86_64 x86_64 GNU/Linux
Jun 14, 2013 · Using POSIX shell functions, and awk math power, just define this (one line) function: calc(){ awk "BEGIN { print $*}"; } Then just execute things like calc 1+1 or calc 5/2. Note: To make the function always available, add it to ~/.bashrc (or your corresponding shell's startup file) Of course, a little script named "calc" with the following ...
