## 27.13. Differences Between Bourne and C Shell Quoting

This article explains quoting in C-type shells by comparing them to Bourne-type shell quoting. If you haven't read Section 27.12 about Bourne shell quoting, please do so now.

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

### 27.13.1. Special Characters

The C shell has a few more special characters in addition to the original Bourne shell:

>     ! { } ~

### 27.13.2. How Quoting Works

Table 27-2 summarizes the rules; you might want to look back at it while you read the examples.

#### Table 27-2. 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 following:

- The exclamation point (`!`) character can be quoted only with a backslash. That's true inside and outside single or double quotes. So you can use history substitution (Section 30.8) 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.

  Section 29.10 shows an amazing pair of aliases that automate complicated C shell 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 unless the line ends with a backslash. In other words, to quote more than one line, type a backslash at the end of each line before the last 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

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