[C shell] Variable operators and Expressions

cited from here

1. Variables

${ var }	The value of variable var .
${ var [ i ]}	Select word or words in position i of var . i can be a single number, a range m - n , a range - n (missing m implies 1), a range m - (missing n implies all remaining words), or * (select all words). i can also be a variable that expands to one of these values.
${# var }	The number of words in var .
${#argv}	The number of command-line arguments.
${argv[ n ]}	Individual arguments on command line (positional parameters). n is a number (1, 12, etc.).
${ n }	Same as ${argv[ n ]} .
${argv[*]}	All arguments on command line.
$*	Same as $argv[*] .
${argv[$#argv]}	The last argument.
${? var }	Return 1 if var is set; 0 if var is not set.
! ${? var }	Return 0 if var is set; 1 if var is not set.
$$	Process number of current shell; useful as part of a filename for creating temporary files with unique names.
$<	Read a line from standard input.

 

2. Expressions

1. * / %

2. + -

Group all other expressions inside ( ). Parentheses are required if the expression contains < , > , & , or | .

3. Operators

3.1 Assignment Operators

=	Assign value.
+= -=	Reassign after addition/subtraction.
*= /= %=	Reassign after multiplication/division/remainder.
&= ^= |=	Reassign after bitwise AND/XOR/OR.
++	Increment.
–	Decrement.

3.2 Arithmetic Operators

* / %	Multiplication; integer division; modulus (remainder).
c+ –	Addition; subtraction.

3.3 Bitwise and Logical Operators

~	Binary inversion (one’s complement).
!	Logical negation.
<< >>	Bitwise left shift; bitwise right shift.
&	Bitwise AND.
^	Bitwise exclusive OR.
|	Bitwise OR.
&&	Logical AND.
||	Logical OR.
{ cmd }	Return 1 if command cmd is successful; 0 otherwise. Note that this is the opposite of cmd ‘s normal return code. The status variable may be more practical.

3.4 Comparison Operators

== !=	Equality; inequality.
<= >=	Less than or equal to; greater than or equal to.
< >	Less than; greater than.
=~	String on left matches a filename pattern on the right containing * , ? , or [ … ] .
!~	String on left does not match a filename pattern containing * , ? , or [ … ] .

3.5 File Inquiry Operators

Command substitution and filename expansion are performed on file before the test is performed.

-d file	The file is a directory.
-e file	The file exists.
-f file	The file is a plain file.
-o file	The user owns the file.
-r file	The user has read permission.
-w file	The user has write permission.
-x file	The user has execute permission.
-z file	The file has zero size.
!	Reverse the sense of any of the above inquiries.

Examples.

The following examples show @ commands and assume n = 4:

Expression	Value of $x
@ x = ($n > 10 || $n < 5)	1
@ x = ($n >= 0 && $n < 3)	0
@ x = ($n << 2)	16
@ x = ($n >> 2)	1
@ x = $n % 2	0
@ x = $n % 3	1

The following examples show the first line of if or while statements:

Expression	Meaning
while ($#argv != 0)	While there are command-line ( argv ) arguments …
if ($today[1] == Fri)	If the first word is Fri …
if ($file !~ *.[zZ])	If the file doesn’t end with .z or .Z …
if ($argv[1] =~ chap?)	If the first argument is chap followed by a single character…
if (-f $argv[1])	If the first argument is a plain file…
if (! -d $tmpdir)	If tmpdir is not a directory…