8.5 Expressions
Expressions
are used in @, if, and while
statements to perform arithmetic, string comparisons, file testing,
and so on. exit and set also specify expressions, as can the
tcsh built-in command filetest. 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 and can be remembered as follows:
* / % + -
Group all other expressions inside parentheses. Parentheses are
required if the expression contains <, >, &, or |.
8.5.1 Operators
Operators
can be one of the following types.
8.5.1.1 Assignment operators
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=
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Assign value.
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+= -=
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Reassign after addition/subtraction.
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*= /= %=
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Reassign after multiplication/division/remainder.
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&= ^= |=
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Reassign after bitwise AND/XOR/OR.
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++
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Increment.
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--
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Decrement.
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8.5.1.2 Arithmetic operators
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* / %
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Multiplication; integer division; modulus (remainder).
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+ -
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Addition; subtraction.
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8.5.1.3 Bitwise and logical operators
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~
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Binary inversion (one's complement).
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!
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Logical negation.
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<< >>
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Bitwise left shift; bitwise right shift.
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&
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Bitwise AND.
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^
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Bitwise exclusive OR.
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Bitwise OR.
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&&
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Logical AND.
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||
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Logical OR.
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{ command
}
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Return 1 if command is successful, 0 otherwise. Note that this is the
opposite of command's normal
return code. The $status variable
may be more practical.
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8.5.1.4 Comparison operators
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= = !=
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Equality; inequality.
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<= >=
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Less than or equal to; greater than or equal to.
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< >
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Less than; greater than.
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8.5.1.5 File inquiry operators
Command substitution and filename
expansion are performed on file before the test
is performed. Operators can be combined (e.g., -ef). The following is a list of the valid
file inquiry operators:
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-b file
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The file is a block special file.
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-c file
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The file is a character special file.
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-d file
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The file is a directory.
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-e file
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The file exists.
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-f file
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The file is a plain file.
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-g file
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The file's set-group-ID bit is set.
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-k file
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The file's sticky bit is set.
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-l file
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The file is a symbolic link.
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-L file
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Apply any remaining operators to symbolic link, not the file it
points to.
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-o file
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The user owns the file.
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-p file
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The file is a named pipe (FIFO).
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-r file
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The user has read permission.
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-s file
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The file has nonzero size.
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-S file
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The file is a socket special file.
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-t file
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file is a digit and is an open file descriptor
for a terminal device.
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-u file
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The file's set-user-ID bit is set.
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-w file
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The user has write permission.
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-x file
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The user has execute permission.
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-X file
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The file is executable and is in the path, or is a shell built-in.
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-z file
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The file has 0 size.
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!
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Reverse the sense of any preceding inquiry.
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Finally, tcsh provides the following
operators, which return other kinds of information:
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-A[:] file
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Last time file was accessed, as the number of seconds since the
epoch. With a colon (:), the result is in timestamp format.
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-C[:] file
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Last time inode was modified. With a colon (:), the result is in
timestamp format.
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-D file
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Device number.
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-F file
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Composite file identifier, in the form
device:inode.
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-G[:] file
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Numeric group ID for the file. With a colon (:), the result is the
group name if known, otherwise the numeric group ID.
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-I file
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Inode number.
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-L file
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The name of the file pointed to by symbolic link
file.
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-M[:] file
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Last time file was modified. With a colon (:), the result is in
timestamp format.
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-N file
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Number of hard links.
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-P[:] file
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Permissions in octal, without leading 0. With a colon (:), the result
includes a leading 0.
|
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-Pmode[:] file
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Equivalent to -P
file ANDed to mode. With a
colon (:), the result includes a leading 0.
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-U[:] file
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Numeric user ID of the file's owner. With a colon
(:), the result is the username if known, otherwise the numeric user
ID.
|
|
-Z file
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The file's size, in bytes.
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8.5.2 Examples
The following examples show @
commands and assume n = 4:
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@ x = ($n > 10 || $n < 5)
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1
|
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@ x = ($n >= 0 && $n <
3)
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0
|
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@ x = ($n << 2)
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16
|
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@ x = ($n >> 2)
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1
|
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@ x = $n % 2
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0
|
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@ x = $n % 3
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1
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The following examples show the first line of if or while
statements:
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while ($#argv != 0)
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While there are arguments . . .
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if ($today[1] = = "Fri")
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If the first word is "Fri". . .
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if (-f $argv[1])
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If the first argument is a plain file. . .
|
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if (! -d $tmpdir)
|
If tmpdir is not a directory. .
.
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