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Builtin Commands 447 in Objective-C Render Code 128 Code Set A in Objective-C Builtin Commands 447




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Builtin Commands 447 using iphone topaint code-128 for asp.net web,windows application QR Codes type: Displays Information About a Command The type builtin (use which under tcsh) provides information about a command:. $ type cat echo who i barcode code 128 for Objective-C f lt cat is hashed (/bin/cat) echo is a shell builtin who is /usr/bin/who if is a shell keyword lt is aliased to "ls -ltrh . tail". The preceding output iPhone barcode 128a shows the files that would be executed if you gave cat or who as a command. Because cat has already been called from the current shell, it is in the hash table (page 957) and type reports that cat is hashed. The output also shows that a call to echo runs the echo builtin, if is a keyword, and lt is an alias.

. read: Accepts User Input One of the most commo ANSI/AIM Code 128 for Objective-C n uses for user-created variables is storing information that a user enters in response to a prompt. Using read, scripts can accept input from the user and store that input in variables. See page 371 for information about reading user input under tcsh.

The read builtin reads one line from standard input and assigns the words on the line to one or more variables:. $ cat read1 echo -n " Go ahead: " read firstline echo "You entered: $firstline" $ ./read1 Go ahead: This is a line. You entered: This is a line.

. The first line of the iPhone ANSI/AIM Code 128 read1 script uses echo to prompt for a line of text. The n option suppresses the following NEWLINE, allowing you to enter a line of text on the same line as the prompt. The second line reads the text into the variable firstline.

The third line verifies the action of read by displaying the value of firstline. The variable is quoted (along with the text string) in this example because you, as the script writer, cannot anticipate which characters the user might enter in response to the prompt. Consider what would happen if the variable were not quoted and the user entered * in response to the prompt:.

$ cat read1_no_quote echo -n "Go ahead: " read firstline echo You entered: $firstline $ ./read1_no_quote Go ahead: * You entered: read1 read1_no_quote script.1 $ ls read1 read1_no_quote script.

1. 448 10 Programming the Bourne Again Shell The ls command lists the same words as the script, demonstrating that the shell expands the asterisk into a list of files in the working directory. When the variable $firstline is surrounded by double quotation marks, the shell does not expand the asterisk. Thus the read1 script behaves correctly:.

$ ./read1 Go ahead: * You entered: REPLY The read builtin incl udes several features that can make it easier to use. For example, when you do not specify a variable to receive read s input, bash puts the input into the variable named REPLY. You can use the p option to prompt the user instead of using a separate echo command.

The following read1a script performs exactly the same task as read1:. $ cat read1a read -p "Go ahe code 128 code set c for Objective-C ad: " echo "You entered: $REPLY". The read2 script prompts for a command line, reads the user s response, and assigns it to the variable cmd. The script then attempts to execute the command line that results from the expansion of the cmd variable:. $ cat read2 read -p "Enter a barcode 128 for Objective-C command: " cmd $cmd echo "Thanks". In the following example, re ad2 reads a command line that calls the echo builtin. The shell executes the command and then displays Thanks. Next read2 reads a command line that executes the who utility:.

$ ./read2 Enter a command: e iPhone Code 128 Code Set A cho Please display this message. Please display this message.

Thanks $ ./read2 Enter a command: who max pts/4 Jun 17 07:50 (:0.0) sam pts/12 Jun 17 11:54 (bravo.

example.com) Thanks. If cmd does not expand into a valid command line, the shell issues an error message:.
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