Qual é a diferença entre 'e'? [duplicado]

Question

Eu tentei criar um arquivo de texto em um script bash.

O comando echo abrange várias linhas e tem algumas aspas duplas "".

#!/bin/bash 

echo "blabla bla bla bla "blabla" 
bla bla " bla bla bla"
and so on and so on

bla bla

blu bla  "bla bla bla "
bla bla" > /root/bin/bla

Existem muitas aspas duplas "" no comando echo que são indesejáveis.

E eu fiz

#!/bin/bash 

echo 'blabla bla bla bla "blabla" 
bla bla " bla bla bla"
and so on and so on

bla bla

blu bla  "bla bla bla "
bla bla' > /root/bin/bla

Gostaria de saber se há alguma diferença entre aspas duplas "e aspas simples"

Qual deles tem maior prioridade? É apenas o fato de que eles são visualmente diferentes?

    

Answer 1

Do manual do bash :

3.1.2.2 Single Quotes

Enclosing characters in single quotes (‘'’) preserves the literal value of each character within the quotes. A single quote may not occur between single quotes, even when preceded by a backslash.

3.1.2.3 Double Quotes

Enclosing characters in double quotes (‘"’) preserves the literal value of all characters within the quotes, with the exception of ‘$’, ‘'’, ‘\’, and, when history expansion is enabled, ‘!’. The characters ‘$’ and ‘'’ retain their special meaning within double quotes (see Shell Expansions). The backslash retains its special meaning only when followed by one of the following characters: ‘$’, ‘'’, ‘"’, ‘\’, or newline. Within double quotes, backslashes that are followed by one of these characters are removed. Backslashes preceding characters without a special meaning are left unmodified. A double quote may be quoted within double quotes by preceding it with a backslash. If enabled, history expansion will be performed unless an ‘!’ appearing in double quotes is escaped using a backslash. The backslash preceding the ‘!’ is not removed. The special parameters ‘*’ and ‘@’ have special meaning when in double quotes (see Shell Parameter Expansion).

Aqui estão algumas demonstrações práticas dos itens acima:

• As aspas duplas permitem avaliar expansões de parâmetros, mas aspas simples não:

$ var=foo
$ echo "$var"
foo
$ echo '$var'
$var

• As aspas duplas permitem a avaliação de escapes de barra invertida, mas as aspas simples não:

$ echo "\"
\
$ echo '\'
\

• As aspas duplas permitem a avaliação de substituições de comandos ( $( , ' ), mas aspas simples não:

$ echo "$(echo bar)"
bar
$ echo '$(echo bar)'
$(echo bar)