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Chapter 5 The C Shell |
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5.4 Expressions
Expressions are used in @ , if , and while statements to perform arithmetic, string comparisons, file testing, etc. exit and set can also specify expressions. Expressions are formed by combining variables and constants with operators that resemble those in the C programming language. Operator precedence is the same as in C but can be remembered as follows:
-
* / % -
+ -
Group all other expressions inside ( )'s. Parentheses are required if the expression contains <, >, &, or |.
5.4.1 Operators
Operators can be one of the following types:
5.4.1.1 Assignment Operators
| = | Assign value. |
| += -= | Reassign after addition/subtraction. |
| *= /= %= | Reassign after multiplication/division/remainder. |
| &= ^= |= | Reassign after bitwise AND/XOR/OR. |
| ++ | Increment |
| - | Decrement. |
5.4.1.2 Arithmetic Operators
| * / % | Multiplication; integer division; modulus (remainder). |
| + - | Addition; subtraction. |
5.4.1.3 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. |
{
command
} |
Return 1 if command is successful; 0 otherwise.
Note that this is the opposite of |
5.4.1.4 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 containing *, ?, or [...]. |
| !~ |
String on left does not match a filename pattern containing *, ?, or [...]. |
5.4.1.5 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 inquiry above. |
5.4.2 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 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... |
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| 5.3 Variables |
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5.5 Command History csh shell |
