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[[]] vs (()) in bash

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ycomb1nator answered on October 1, 2021 Popularity 3/10 Helpfulness 1/10

answer [[]] vs (()) in bash

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[[]] vs (()) in bash

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Operator 			Purpose 								Example
[[ expression ]] 	Conditional expressions 				if [[ $string == “linux” ]]; then echo “The string is linux”
[ expression ] 		Basic Conditional expressions 			if [ -f $file ]; then echo “The file exists”
( command ) 		Run commands in a subshell environment 	(cd /home/user/directory && ls)
(( expression )) 	Arithmetic operations 					if (( $a + $b > $c )); then echo “The sum of a and b is greater than c”

Popularity 3/10 Helpfulness 1/10 Language whatever

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Tags: bash whatever

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Contributed on Feb 05 2024

ycomb1nator

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() vs {} bash

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() 
- Placing a list of commands between parentheses causes a subshell environment
to be created, and each of the commands in list to be executed in that subshell.
Since the list is executed in a subshell, variable assignments do not remain 
in effect after the subshell completes.

{}
- Placing a list of commands between curly braces causes the list to be executed
in the current shell context. No subshell is created. The semicolon (or newline)
following list is required.

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Tags: bash

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Contributed on Oct 01 2021

GitPaulo

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$() vs `` bash

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$() or `` is called command subsitution

They are the same. Command subsitution allows the output of a command to 
replace the command identifier.

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Contributed on Oct 01 2021

GitPaulo

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$() vs () bash

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$(cmd) substitutes the result of cmd as a string, whereas (cmd; cmd) run a list of commands in a subprocess.

If you want to put the output of one or more commands into a variable use the $( cmd ) form.

However if you want to run a number of commands and treat them as a single unit use the () form.

The latter is useful when you want to run a set of commands in the background.

Popularity 8/10 Helpfulness 2/10 Language shell

Source: stackoverflow.com

Tags: bash shell she

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Contributed on Nov 06 2021

Is Mayonnaise a Programming Language?

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[[]] vs (()) in bash

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