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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 but can be remembered as follows:

  1. * / %

  2. + -

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:

8.5.1.5. File inquiry operators

Command substitution and filename expansion are performed on file before the test is performed. tcsh permits operators to be combined (e.g., -ef). The following is a list of the valid file inquiry operators:

Operator Description
-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 0 size.
!

Reverse the sense of any preceding inquiry.

Some additional operators specific to tcsh are:

Operator Description
-b file

The file is a block special file.

-c file

The file is a character special 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.

-p file

The file is a named pipe (FIFO).

-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.

-X file

The file is executable and is in the path or is a shell built-in.

Finally, tcsh provides the following operators, which return other kinds of information:

Operator Description
-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 to 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.



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