| Expressions are used in @ (the C shell math operator), 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. It is easiest to just remember the following precedence rules: * / % + - Group all other expressions inside ( )s; parentheses are required if the expression contains <, >, &, or |
5.5.1. Operators Operators can be one of the following types. 5.5.1.1. Assignment operators Operator | Description |
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= | Assign value. | += -= | Reassign after addition/subtraction. | *= /= %= | Reassign after multiplication/division/remainder. | &= ^= |= | Reassign after bitwise AND/XOR/OR. | ++ | Increment. | -- | Decrement. |
5.5.1.2. Arithmetic operators Operator | Description |
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* / % | Multiplication; integer division; modulus (remainder). | + - | Addition; subtraction. |
5.5.1.3. Bitwise and logical operators Operator | Description |
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~ | Binary inversion (one's complement). | ! | Logical negation. | << >> | Bitwise left shift; bitwise right shift. | & | Bitwise AND. | ^ | Bitwise exclusive OR. | | | Bitwise OR. | && | Logical AND (short-circuit). | || | Logical OR (short-circuit). | { command } | 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. |
5.5.1.4. Comparison operators Operator | Description |
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== != | Equality; inequality. | <= >= | Less than or equal to; greater than or equal to. | < > | Less than; greater than. | =~ | String on left matches a filename pattern on right containing *, ?, or [...]. | !~ | String on left does not match a filename pattern on right containing *, ?, or [...]. |
5.5.1.5. 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. Operator | Description |
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-b file | The file is a block special file. | -c file | The file is a character special file. | -d file | The file is a directory. | -e file | The file exists. | -f file | The file is a plain file. | -g file | The file's set-group-ID bit is set. | -k file | The file's sticky bit is set. | -l file | The file is a symbolic link. | -L file | Apply any remaining operators to symbolic link, not the file it points to. | -o file | The current user owns the file. | -p file | The file is a named pipe (FIFO). | -r file | The current user has read permission. | -s file | The file has nonzero size. | -S file | The file is a socket special file. | -t file | file is a digit and is an open file descriptor for a terminal device. | -u file | The file's set-user-ID bit is set. | -w file | The current user has write permission. | -x file | The current user has execute permission. | -X file | The file is executable and is in the path, or is a shell built-in. | -z file | The file has zero size. | ! | Reverse the sense of any following inquiry, which may be any of the tests in this table. |
Finally, tcsh provides the following operators, which return other kinds of information. Operator | Description |
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-A[:] file | Last time file was accessed, as the number of seconds since the epoch. With a colon (:), the result is in timestamp format. | -C[:] file | Last time inode was modified. With a colon (:), the result is in timestamp format. | -D file | Device number. | -F file | Composite file identifier, in the form device:inode. | -G[:] file | Numeric group ID for the file. With a colon (:), the result is the group name if known, otherwise the numeric group ID. | -I file | Inode number. | -L file | The name of the file pointed to by symbolic link file. | -M[:] file | Last time file was modified. With a colon (:), the result is in timestamp format. | -N file | Number of hard links. | -P[:] file | Permissions in octal, without leading 0. With a colon (:), the result includes a leading 0. | -Pmode[:] file | Equivalent to -P file ANDed with mode. With a colon (:), the result includes a leading 0. | -U[:] file | 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 | The file's size, in bytes. |
These operators may only be used in multioperator tests, and they must be the last operator in such tests. 5.5.2. Examples The following examples show @ commands and assume n = 4. Expression | Value of $x |
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@ x = ($n > 10 || $n < 5) | 1 | @ x = ($n >= 0 && $n < 3) | 0 | @ x = ($n << 2) | 16 | @ x = ($n >> 2) | 1 | @ x = $n % 2 | 0 | @ x = $n % 3 | 1 |
The following examples show the first line of if or while statements. Expression | Meaning |
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while ($#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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