Thủ Thuật Hướng dẫn The if statement can only return a binary zero or one condition Mới Nhất
Lê Hoàng Hưng đang tìm kiếm từ khóa The if statement can only return a binary zero or one condition được Update vào lúc : 2022-12-26 07:46:09 . Với phương châm chia sẻ Kinh Nghiệm Hướng dẫn trong nội dung bài viết một cách Chi Tiết Mới Nhất. Nếu sau khi Read Post vẫn ko hiểu thì hoàn toàn có thể lại phản hồi ở cuối bài để Mình lý giải và hướng dẫn lại nha.The test command evaluates the Expression parameter, and if the expression value is True, returns a zero (True) exit value. Otherwise, the test command returns a nonzero (False) exit value. The test command also returns a nonzero exit value if there are no parameters.
Nội dung chính Show- Exit StatusWhich commands displays a file's contents one screen a time ____?Which command will display the exit status code on the screen?Which symbol represents a permission that has not been granted?What permission is needed to run a script quizlet?
Requirements:
- In the second form of the command, the [ ] (brackets) must be surrounded by blank spaces.You must test explicitly for file names in the C shell. File-name substitution (globbing) causes the shell script to exit.
Functions and operators are treated as separate parameters by the test command. The Expression parameter refers to a statement that is checked for a true or false condition. The following functions are used to construct this parameter:
ItemDescription-b FileNameReturns a True exit value if the specified FileName exists and is a block special file.-c FileNameReturns a True exit value if the specified FileName exists and is a character special file.-d FileNameReturns a True exit value if the specified FileName exists and is a directory.-e FileNameReturns a True exit value if the specified FileName exists.-f FileNameReturns a True exit value if the specified FileName exists and is a regular file.-g FileNameReturns a True exit value if the specified FileName exists and its Set Group ID bit is set.-h FileNameReturns a True exit value if the specified FileName exists and is a symbolic link.-k FileNameReturns a True exit value if the specified FileName exists and its sticky bit is set.-L FileNameReturns a True exit value if the specified FileName exists and is a symbolic link.-n String1Returns a True exit value if the length of the String1 variable is nonzero.-p FileNameReturns a True exit value if the specified FileName exists and is a named pipe (FIFO).-r FileNameReturns a True exit value if the specified FileName exists and is readable by the current process.-s FileNameReturns a True exit value if the specified FileName exists and has a size greater than 0.-t FileDescriptorReturns a True exit value if the file with a file descriptor number of FileDescriptor is open and associated with a terminal.-u FileNameReturns a True exit value if the specified FileName exists and its Set User ID bit is set.-w FileNameReturns a True exit value if the specified FileName exists and the write flag is on. However, the FileNamewill not be writable on a read-only file system even if test indicates true.-x FileNameReturns a True exit value if the specified FileName exists and the execute flag is on. If the specified file exists and is a directory, the True exit value indicates that the current process has permission to search in the directory.-z String1Returns a True exit value if the length of the String1 variable is 0 (zero).String1= String2Returns a True exit value if the String1 and String2 variables are identical.String1!=String2Returns a True exit value if the String1 and String2 variables are not identical.String1Returns a True exit value if the String1 variable is not a null string.Integer1 -eq Integer2Returns a True exit value if the Integer1 and Integer2 variables are algebraically equal. Any of the comparisons -ne, -gt, -ge, -lt, and -le can be used in place of -eq.file1 -nt file2True if file1 is newer than file2.file1 -ot file2True if file1 is older than file2.file1 -ef file2True if file1 is another name for file2.
These functions can be combined with the following operators:
ItemDescription!Unary negation operator-aBinary AND operator-oBinary OR operator ( that is, the -a operator has higher precedence than the -o operator)(Expression)Parentheses for grouping
Exit Status
This command returns the following exit values:
ItemDescription0The Expression parameter is true.1The Expression parameter is false or missing.>1An error occurred.
Examples
To test whether a file exists and is not empty, enter the following command:if test ! -s "$1" then echo $1 does not exist or is empty. fiIf the file specified by the first positional parameter to the shell procedure, $1, does not exist, the test command displays an error message. If $1 exists and has a size greater than 0, the test command displays nothing.
Note: There must be a space between the -s function and the file name.The quotation marks around $1 ensure that the test works properly even if the value of $1 is a null string. If the quotation marks are omitted and $1 is the empty string, the test command displays the error message test: argument expected.
To do a complex comparison, type:if [ $# -lt 2 -o ! -e "$1" ] then exit fiIf the shell procedure is given fewer than two positional parameters or the file specified by $1 does not exist, then the shell procedure exits. The special shell variable $# represents the number of positional parameters entered on the command line that starts this shell procedure.
Which commands displays a file's contents one screen a time ____?
Combining the cat command with the pg command allows you to read the contents of a file one full screen a time. You can also display the contents of files by using input and output redirection.Which command will display the exit status code on the screen?
To display the exit code for the last command you ran on the command line, use the following command: $ echo $?Which symbol represents a permission that has not been granted?
43 Cards in this Set.What permission is needed to run a script quizlet?
To run a script file, you need both read and execute permission. Tải thêm tài liệu liên quan đến nội dung bài viết The if statement can only return a binary zero or one condition