The Bash manual has this to say:
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.
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: ‘$’, ‘`’, ‘"’, ‘\’, or newline. Within double quotes, backslashes that are followed by one of these characters are removed. Backslashes preceding characters without a special meaning are left unmodified. A double quote may be quoted within double quotes by preceding it with a backslash. If enabled, history expansion will be performed unless an ‘!’ appearing in double quotes is escaped using a backslash. The backslash preceding the ‘!’ is not removed.
The special parameters ‘*’ and ‘@’ have special meaning when in double quotes (see Shell Parameter Expansion).
Below is a simple bash script which explains the difference between single and double quotes:
Single Quotes
Enclosing characters in single quotes (‘'’) preserves the literal value of each character within the quotes. A single quote may not occur between single quotes, even when preceded by a backslash.
Double Quotes
Enclosing characters in double quotes (‘"’) preserves the literal value of all characters within the quotes, with the exception of ‘$’, ‘`’, ‘\’, 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).
Below is a simple bash script which explains the difference between single and double quotes:
Source: cat quotes.sh
#!/bin/bash
linuxpoison=blog
# Using single quotes, preserves the literal value of all characters within the quotes.
echo 'This is example of $single quotes from $linuxpoison'
# Using double quotes, the value of $ is expanded.
echo "This is example of $double quotes from $linuxpoison"
Output: ./quotes.sh
This is example of $single quotes from $linuxpoison
This is example of quotes from blog
#!/bin/bash
linuxpoison=blog
# Using single quotes, preserves the literal value of all characters within the quotes.
echo 'This is example of $single quotes from $linuxpoison'
# Using double quotes, the value of $ is expanded.
echo "This is example of $double quotes from $linuxpoison"
Output: ./quotes.sh
This is example of $single quotes from $linuxpoison
This is example of quotes from blog
0 comments:
Post a Comment