1

I tried to create a text file in a bash script.

The echo command spans multiple lines and has some double quotes "".

#!/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

There are many double quotes "" in echo command that is undesirable.

And I did 

#!/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

I wondered if there are any difference between double quote " and single quote '

Which one has higher priority? Is it just the fact that they are visually different?

Chris Down
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Armando
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1 Answers1

9

From the bash manual:

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).

Here are some practical demonstrations of the above:

  • Double quotes allow evaluation of parameter expansions, but single quotes do not:
$ var=foo
$ echo "$var"
foo
$ echo '$var'
$var
  • Double quotes allow evaluation of backslash escapes, but single quotes do not:
$ echo "\\"
\
$ echo '\\'
\\
  • Double quotes allow evaluation of command substitutions ($(, `), but single quotes do not:
$ echo "$(echo bar)"
bar
$ echo '$(echo bar)'
$(echo bar)
Chris Down
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