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Feb 20, 2011 · 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.
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 ...
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.
Apr 5, 2014 · 1. They could be the same program, but they have different meanings. The program name tells it all. /bin/false is intended to return a false value. It is run as program. /bin/nologin is intended to indicate to the user that no login is permitted for an account. (It is used a login shell.) Share.
cw is designed to simulate the environment of the commands being executed, so that if a person types 'du', 'df', 'ping', etc. in their shell it will automatically color the output in real-time according to a definition file containing the color format desired. cw has support for wildcard match coloring, tokenized coloring, headers/footers, case scenario coloring, command line dependent ...
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.
gksu and gksudo are graphical front-ends to su and sudo respectively. They allow you to run X Window programs as root with no hassle. They are part of Gnome. Type. gksu command --option argument. and enter the root password, or type. gksudo command --option argument. and enter your password (if authorized to run sudo).
Jun 19, 2015 · Interestingly, the shell will even do the twiddle thing ~ and << left and >> right SHIFTs. And so if a is true OR b^100 is true, the expansion evals to 1, matches the comparison -eq [test ] and the shell continues to evaluate the rest of && some commands. It is usually easier to evaluate/compare integers in that way than to try to string ...
A shell assignment is a single word, with no space after the equal sign. So what you wrote assigns an empty value to thefile; furthermore, since the assignment is grouped with a command, it makes thefile an environment variable and the assignment is local to that particular command, i.e. only the call to ls sees the assigned value.
Jan 30, 2017 · The reason why this comparison doesn't work well with a hyphenated date string is the shell assumes a number with a leading 0 is an octal, in this case the month "07". There have been various solutions proposed but the quickest and easiest is to strip out the hyphens. Bash has a string substitution feature that makes this quick and easy then the comparison can be performed as an arithmetic ...
