[Chapter 5] 5.2 Syntax

5.2 Syntax

This section describes the many symbols peculiar to the C shell. The topics are arranged as follows:

Special files
Filename metacharacters
Quoting
Command forms
Redirection forms

5.2.1 Special Files

~/.cshrc	Executed at each instance of shell invocation.
~/.login	Executed by login shell after .cshrc at login.
~/.logout	Executed by login shell at logout.
~/.history	History list saved from previous login.
/etc/passwd	Source of home directories for `~` name abbreviations. (May come from NIS or NIS+ instead.)

5.2.2 Filename Metacharacters

Metacharacter	Description
`*`	Match any string of zero or more characters.
`?`	Match any single character.
`[` abc ...`]`	Match any one of the enclosed characters; a hyphen can be used to specify a range (e.g., a-z, A-Z, 0-9).
`{` abc `,` xxx `,` ...`}`	Expand each comma-separated string inside braces. The strings need not match actual filenames.
`~`	Home directory for the current user.
`~` name	Home directory of user name .

5.2.2.1 Examples

% ls new*

         Match new and new.1

% cat ch?

         Match ch9 but not ch10

% vi [D-R]*

       Match files that begin with uppercase D through R

% ls {ch,app}?

    Expand, then match ch1, ch2, app1, app2

% mv info{,.old}

  Expands to mv info info.old

% cd ~tom

         Change to tom's home directory

5.2.3 Quoting

Quoting disables a character's special meaning and allows it to be used literally, as itself. The characters in the following table have special meaning to the C shell.

Character	Meaning
`;`	Command separator
`&`	Background execution
`( )`	Command grouping
`\|`	Pipe
`* ? [ ] ~`	Filename metacharacters
`{ }`	String expansion characters; usually don't require quoting
`< > & !`	Redirection symbols
`! ^`	History substitution, quick substitution
`" ' \`	Used in quoting other characters
`	Command substitution
`$`	Variable substitution
`space tab newline`	Word separators

These characters can be used for quoting:

" "

Everything between " and " is taken literally, except for the following characters that keep their special meaning:

$: Variable substitution will occur.
`: Command substitution will occur.
": This marks the end of the double quote.
\: Escape next character.
!: The history character.
newline: The newline character.

' '

Everything between ' and ' is taken literally except for ! (history) and another ' , and newline.

\

The character following a \ is taken literally. Use within "" to escape " , $ , ` , and newline. Use within '' to escape newlines. Often used to escape itself, spaces, or newlines. Always needed to escape a history character (usually ! ).

5.2.3.1 Examples

% echo 'Single quotes "protect" double quotes'


Single quotes "protect" double quotes

% echo "Don't double quotes protect single quotes too?"


Don't double quotes protect single quotes too?

% echo "You have `ls|wc -l` files in `pwd`"


You have       43 files in /home/bob

% echo The value of \$x is $x


The value of $x is 100

5.2.4 Command Forms

cmd `&`	Execute cmd in background.
cmd1 `;` cmd2	Command sequence; execute multiple cmd s on the same line.
`(` cmd1 `;` cmd2 `)`	Subshell; treat cmd1 and cmd2 as a command group.
cmd1 `\|` cmd2	Pipe; use output from cmd1 as input to cmd2 .
cmd1 ` cmd2 `	Command substitution; use cmd2 output as arguments to cmd1 .
cmd1 `&&` cmd2	AND; execute cmd1 and then (if cmd1 succeeds) cmd2 . This is a "short-circuit" operation; cmd2 is never executed if cmd1 fails.
cmd1 `\|\|` cmd2	OR; execute either cmd1 or (if cmd1 fails) cmd2 . This is a "short-circuit" operation; cmd2 is never executed if cmd1 succeeds.

5.2.4.1 Examples

% nroff file > file.out &

            Format in the background

% cd; ls

                             Execute sequentially

% (date; who; pwd) > logfile

         All output is redirected

% sort file | pr -3 | lp

             Sort file, page output, then print

% vi `grep -l ifdef *.c`

             Edit files found by grep

% egrep '(yes|no)' `cat list`

        Specify a list of files to search

% grep XX file && lp file

            Print file if it contains the pattern,

% grep XX file || echo XX not found

  otherwise, echo an error message

5.2.5 Redirection Forms

File Desciptor	Name	Common Abbreviation	Typical Default
0	Standard input	stdin	Keyboard
1	Standard output	stdout	Terminal
2	Standard error	stderr	Terminal

The usual input source or output destination can be changed, as seen in the following sections.

5.2.5.1 Simple redirection

cmd > file: Send output of cmd to file (overwrite).
cmd >! file: Same as above, even if noclobber is set.
cmd >> file: Send output of cmd to file (append).
cmd >>! file: Same as above, but write to file even if noclobber is set.
cmd < file: Take input for cmd from file .
cmd << text: Read standard input up to a line identical to text (text can be stored in a shell variable). Input is usually typed at the terminal or in the shell program. Commands that typically use this syntax include cat , echo , ex , and sed . If text is quoted (using any of the shell-quoting mechanisms), the input is passed through verbatim.

5.2.5.2 Multiple redirection

cmd `>&` file	Send both standard output and standard error to file .
cmd `>&!` file	Same as above, even if `noclobber` is set.
cmd `>>&` file	Append standard output and standard error to end of file .
cmd `>>&!` file	Same as above, but append to or create file even if `noclobber` is set.
cmd1 `\|&` cmd2	Pipe standard error together with standard output.
`(` cmd `>` f1 `) >&` f2	Send standard output to file f1 , standard error to file f2 .
cmd `\| tee` files	Send output of cmd to standard output (usually the terminal) and to files . (See the Example in Chapter 2, Unix Commands , under tee .)

5.2.5.3 Examples

% cat part1 > book


% cat part2 part3 >> book


% mail tim < report


% cc calc.c >& error_out


% cc newcalc.c >&! error_out


% grep Unix ch* |& pr


% (find / -print > filelist) >& no_access



% sed 's/^/XX /g' << "END_ARCHIVE"


This is often how a shell archive is "wrapped",


bundling text for distribution.  You would normally


run sed from a shell program, not from the command line.


"END_ARCHIVE"


XX This is often how a shell archive is "wrapped",
XX bundling text for distribution.  You would normally
XX run sed from a shell program, not from the command line.