Difference between revisions of "Quoting"

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Your bash shell understand special characters with special meanings. For example, $var is used to display the variable value. You can enable or disable the meaning of a special character by enclosing them into a single or double quotes. This is also useful to suppress warnings and error messages while writing the shell scripts.  
+
Your bash shell understand special characters with special meanings. For example, $var is used to display the variable value. Bash expands variables and [[wildcards]], for example:
 +
<source lang="bash">echo $PATH
 +
echo $PS1
 +
echo /etc/*.conf</source>
 +
However, sometime you do not wish to use variables or [[wildcards]]. For example, do not print value of $PATH, but just print $PATH on screen as a word. You can enable or disable the meaning of a special character by enclosing them into a single or double quotes. This is also useful to suppress warnings and error messages while writing the shell scripts.  
 +
<source lang="bash">echo "Path is $PATH"</source>
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OR
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<source lang="bash">echo 'I want to print $PATH'</source>
 
==Quoting==
 
==Quoting==
 
There are three types of quotes  
 
There are three types of quotes  

Revision as of 14:34, 12 September 2009

Your bash shell understand special characters with special meanings. For example, $var is used to display the variable value. Bash expands variables and wildcards, for example:

echo $PATH
echo $PS1
echo /etc/*.conf

However, sometime you do not wish to use variables or wildcards. For example, do not print value of $PATH, but just print $PATH on screen as a word. You can enable or disable the meaning of a special character by enclosing them into a single or double quotes. This is also useful to suppress warnings and error messages while writing the shell scripts.

echo "Path is $PATH"

OR

echo 'I want to print $PATH'

Quoting

There are three types of quotes

Quote type Name Meaning Example
" Double Quotes The double quote ( "quote" ) protects everything enclosed between two double quote marks except $, ', " and \.
Use the double quotes when you want variables and command substitution.

echo "$SHELL"
echo "Today is $(date)"

 
' Single quotes The single quote ( 'quote' ) protects everything enclosed between two single quote marks.
It is used to turn off the special meaning of all characters.

echo '$SHELL'
echo 'Today is $(date)'

 
` Back quote Use back quote ( `command-name` ) to execute command and replace a command with its output
within the same command-line. However, $(command-name) is encouraged syntax for substitution as it is recommended
by POSIX standard and it improves script readability.

echo "Today is `date`"
echo "Today is $(date)"

 

Backslash

The backslash ( \ ) alters the special meaning of the ' and " i.e. it will escape or cancel the special meaning of the next character. The following will display filename in double quote:

FILE="/etc/resolv.conf"
echo "File is \"$FILE\" "

Sample Outputs:

File is "/etc/resolv.conf"

The following will remove the special meaning of the dollar ( $ ) sign:

FILE="/etc/resolv.conf"
echo "File is \$FILE "

Sample Outputs:

File is $FILE