whats the function of brackets here ?

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01-08-2011

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whats the function of brackets here ?

Hello,

as the title reads, in a control flow like "if" what's the function of brackets ?

Code:

if  condition  then ...

Code:

if  [[ condition ]]  then ...

Since I saw people using them I wonder whether they are just inserts for code clearness or for the reliability ?

thanks for your help

Regards

Oddant

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Good afternoon:

Quote:

Originally Posted by Oddant

<snip>

Code:

if  condition  then ...

should be:

Code:

if command; then ...

This executes the specified command, and then executes the "then" block if the command exited with a true status ($? is 0).

Quote:

Originally Posted by Oddant

<snip>

Code:

if  [[ condition ]] then ...

should be:

Code:

if [[ condition ]]; then ...

which equivalent to:

Code:

if test condition; then ...

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ok that was helpful thanks even though it didn't answer the main question.

Are those brackets important to be written ? or Are those brackets written just for a better human-readability ?

thanks anyway

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While the brackets are for better human-readability, they are important: if command; then ... is not the same if [[ condition ]]; then ... (unless command happens to be test).

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We need to know what Shell you are using.

In general (and there are exceptions)

Code:

if [[ Conditional Expression  ]]
if [ Test ]

You will find in the "man" pages for your Shell that there is a clear definition of Conditional Expression as distinct from Test. Some common enquiries like "-f" are available in both syntaxes but there are many differences and exceptions.

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01-09-2011

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Quote:

Originally Posted by m.d.ludwig

[..]

Code:

if [[ condition ]]; then ...

which equivalent to:

Code:

if test condition; then ...

[ ... ] is a synonym for test , while [[ ... ]] is a conditional expression, which is not the same. They are different beasts...

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Quote:

Originally Posted by methyl

We need to know what Shell you are using.

In general (and there are exceptions)

Code:

if [[ Conditional Expression  ]]
if [ Test ]

You will find in the "man" pages for your Shell that there is a clear definition of Conditional Expression as distinct from Test. Some common enquiries like "-f" are available in both syntaxes but there are many differences and exceptions.

I'm using bash

Thanks for these replies guys, they are helpful

Regards

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