[Chapter 5] 5.2 Syntax

5.2 Syntax

This subsection 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.
~/.history	History list saved from previous login.
~/.login	Executed by login shell after .cshrc at login.
~/.logout	Executed by login shell at logout.
/etc/passwd	Source of home directories for ~`name` abbreviations.

5.2.2 Filename Metacharacters

*	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.
~	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.
% 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 following characters have special meaning to the C shell:

;	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.
`newline space tab`	Word separators.

The characters below 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.

' '

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 `. 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 "Well, isn't that \"special\"?"
Well, isn't that "special"?
% 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`.
`cmd1` \|\| `cmd2`	OR; execute either `cmd1` or (if `cmd1` fails) `cmd2`.

5.2.4.1 Examples

% nroff file &	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		Common	Typical
Descriptor	Name	Abbreviation	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 follows:

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 create `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 on the screen or in the shell program. Commands that typically use this syntax include cat, echo, ex, and sed. If `text` is enclosed in quotes, standard input will not undergo variable substitution, command substitution, etc.

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 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 Section 2 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.


5.1 Overview of Features		5.3 Variables