What do double square brackets mean in bash?

What do double square brackets mean in bash?

The double square brackets can be used for pattern matching, parameter expansion, and they do not allow word splitting. Using double square brackets helps to avoid logic errors in Bash scripts. In the double square brackets, the && , || , < and > operators work while giving errors in the test command.

What do double parentheses mean in bash?

construct permits arithmetic expansion and evaluation. In its simplest form, a=$(( 5 + 3 )) would set a to 5 + 3, or 8. However, this double-parentheses construct is also a mechanism for allowing C-style manipulation of variables in Bash, for example, (( var++ )). Example 8-5.

What is the difference between using and == in bash double square brackets?

Double Brackets i.e. [[]] is an enhanced (or extension) version of standard POSIX version, this is supported by bash and other shells(zsh,ksh). In bash, for numeric comparison we use eq , ne , lt and gt , with double brackets for comparison we can use == , !=

What is double brackets in shell script?

The double bracket is a “compound command” where as test and the single bracket are shell built-ins (and in actuality are the same command). Thus, the single bracket and double bracket execute different code. The test and single bracket are the most portable as they exist as separate and external commands.

What does double brackets mean in Linux?

Double Brackets are a bash ism To use double brackets your shebang should be #!/bin/bash not #!/bin/sh . Since sh on macOS is bash pretending to be sh , double brackets will still work with the wrong shebang, but then your script might break on other platforms where a different shell might be pretending to be sh .

What does double square brackets mean in Python?

Select a column or columns in a dataframe With one column name, single pair of brackets returns a Series, while double brackets return a dataframe.

What does a double parentheses mean?

The double parentheses indicate an interpolation which would normally be indicated with brackets: But he told me the U.S. military said he couldn’t come because of the [State Department] travel advisory here.

What does double square brackets mean in Java?

Square brackets [] would indicate an array. In your case of code: public double[] MethodName(){ …. } You have a public method MethodName which returns an array. Double indicates what type the array is, i.e. stores an array of objects of type double.

What do two brackets next to each other mean in Python?

Square brackets are used to define lists, but also to get things from lists. When you have a list of lists and want something from an inner list, you need to get that inner list (using brackets) and then get the desired thing inside (using brackets again).