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.

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