[Chapter 5] 5.2 Syntax - e-Reading Library

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