[Chapter 8] 8.15 Differences Between Bourne and C Shell Quoting

8.15 Differences Between Bourne and C Shell Quoting

This article explains quoting in the C shell by comparing it to Bourne shell quoting. If you haven't read article 8.14 about Bourne shell quoting, please do.

As in the Bourne shell, the overall idea of C shell quoting is: quoting turns off (disables) the special meaning of characters . There are three quoting characters: a single quote (' ), a double quote (" ), and a backslash (\ ).

8.15.1 Special Characters

The C shell has several more special characters than the Bourne shell:

! { } ~

8.15.2 How Quoting Works

Table 8.2 summarizes the rules; you might want to look back at it while you read the examples.

Table 8.2: C Shell Quoting Characters
Quoting Character	Explanation
'`xxx` '	Disable all special characters in `xxx` except `!` .
"`xxx` "	Disable all special characters in `xxx` except `$` ,`, and `!` .
\`x`	Disable special meaning of character `x` . At end of line, a `\` treats the newline character like a space (continues line).

The major differences between C and Bourne shell quoting are:

The exclamation point (! ) character can only be quoted with a backslash. That's true inside and outside single or double quotes. So, you can use history substitution ( 11.7 ) inside quotes. For example:
```
% 

grep intelligent engineering file*.txt


grep: engineering: No such file or directory
% 

grep '!:1-2' !:3


grep 'intelligent engineering' file*.txt
    ...
```
In the Bourne shell, inside double quotes, a backslash (\ ) stops variable and command substitution (it turns off the special meaning of $ and ` ).

In the C shell, you can't disable the special meaning of $ or ` inside double quotes. You'll need a mixture of single and double quotes. For example, searching for the string use the `-c' switch takes some work:
```
% 

fgrep "use the \`-c' switch" *.txt


Unmatched \`.
% 

fgrep 'use the \`-c\' switch' *.txt


Unmatched '.
% 

fgrep "use the "'`-c'"' switch" *.txt


hints.txt:Be sure to use the `-c' switch.
```
Article 10.8 shows an amazing pair of aliases that automate complicated quoting problems like this.
In the Bourne shell, single and double quotes include newline characters. Once you open a single or double quote, you can type multiple lines before the closing quote.

In the C shell, if the quotes on a command line don't match, the shell will print an error. To quote more than one line, type a backslash at the end of each line. Inside single or double quotes, the backslash-newline becomes a newline. Unquoted, backslash-newline is an argument separator:
```
% 

echo "one\




two" three\




four


one
two three four
```

- JP