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.

2018年5月22日 · Stack Exchange Network. Stack Exchange network consists of 183 Q&A communities including Stack Overflow, the largest, most trusted online community for developers to learn, share their knowledge, and build their careers.

The process inherits stdin, stdout, and stderr from the shell. Therefore it is also connected to the same terminal. If the shell receives a SIGHUP, it also sends a SIGHUP to the process (which normally causes the process to terminate). Otherwise the shell waits (is blocked) until the process terminates or gets stopped.

pushd, popd, and dirs are shell builtins which allow you manipulate the directory stack. This can be used to change directories but return to the directory from which you came. For example start up with the following directories: $ pwd /home/saml/somedir $ ls dir1 dir2 dir3 pushd to dir1

As already suggested, use "tr -d '[:space:]'", BUT if that doesn't work, possibly on an older Unix system, one needs to cover all these characters:

More on that at: Why is using a shell loop to process text considered bad practice? If it's not about text processing and you do need to run some command per line of a file, also note GNU xargs where you can do: xargs -rd'\n' -I@ -a input.txt cp -- @ @.back for instance.

2014年3月19日 · Stack Exchange Network. Stack Exchange network consists of 183 Q&A communities including Stack Overflow, the largest, most trusted online community for developers to learn, share their knowledge, and build their careers.

2013年6月14日 · 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 ...

2020年12月10日 · That works fine. But how can I make sure that the copy process went without errors (read/write errors from hard disc drives)? It is enough to consider that shell variable $? a 0 after copying returns?

From vi, if you issue the command :sp, the screen splits into two "views", allowing you to edit more than one file from the same terminal. Along those same lines, is there a way to have multiple ...