BASH: ¿Admite variables condicionales como var = "test"? "1": "2"

Question

Soy nuevo en bash pero he hecho muchos PHP y Javascript.

¿Existe algún tipo de equivalencia a este PHP?

$default = 10; 
$var = (!$var) ? $default : $var; 

Gracias

Answer 1

Sí, lo hace:

var=${var:-10} 

Incluso con otras variables:

unset var 
export def=99 
echo ${var:-${def}} # gives '99' 
export var=7 
echo ${var:-${def}} # gives '7' 

Answer 2

Sí!

Desde la página del manual:

${parameter:-word} 
     Use Default Values. If parameter is unset or null, the expansion of word 
     is substituted. Otherwise, the value of parameter is substituted. 
${parameter:=word} 
     Assign Default Values. If parameter is unset or null, the expansion of word 
     is assigned to parameter. The value of parameter is then substituted. 
     Positional parameters and special parameters may not be assigned to in this way. 
${parameter:?word} 
     Display Error if Null or Unset. If parameter is null or unset, the expansion of word (or a message to 
     that effect if word is not present) is written to the standard error and the shell, if it is not inter‐ 
     active, exits. Otherwise, the value of parameter is substituted. 
${parameter:+word} 
     Use Alternate Value. If parameter is null or unset, nothing is substituted, otherwise the expansion of 
     word is substituted. 

Answer 3

$ default=10 
$ var=${var:-$default} 
$ echo $var 
10 
$ var=9 
$ var=${var:-$default} 
$ echo $var 
9