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$ echo tmp* $max tmp1 tmp2 tmp3 sonar $ echo "tmp* $max" tmp* sonar $ echo "tmp* $max" tmp* $max in Objective-C Drawer code-128c in Objective-C $ echo tmp* $max tmp1 tmp2 tmp3 sonar $ echo "tmp* $max" tmp* sonar $ echo "tmp* $max" tmp* $max

$ echo tmp* $max tmp1 tmp2 tmp3 sonar $ echo "tmp* $max" tmp* sonar $ echo "tmp* $max" tmp* $max use iphone code 128a implement toproduce code 128a on objective-c Java The shell di barcode standards 128 for Objective-C stinguishes between the value of a variable and a reference to the variable and does not expand ambiguous file references if they occur in the value of a variable. As a consequence you can assign to a variable a value that includes special characters, such as an asterisk (*)..

Levels of expansion In the next code 128 barcode for Objective-C example, the working directory has three files whose names begin with letter. When you assign the value letter* to the variable var, the shell does not expand the ambiguous file reference because it occurs in the value of a variable (in the assignment statement for the variable). No quotation marks surround the string letter*; context alone prevents the expansion.

After the assignment the set builtin (with the help of grep) shows the value of var to be letter*.. $ ls letter* letter1 letter2 $ var=letter* letter3 Summary . $ set grep var var="letter*" $ echo "$var" $var $ echo "$var" letter* $ echo $var letter1 letter2 letter3 The three ec ho commands demonstrate three levels of expansion. When $var is quoted with single quotation marks, the shell performs no expansion and passes the character string $var to echo, which displays it. With double quotation marks, the shell performs variable expansion only and substitutes the value of the var variable for its name, preceded by a dollar sign.

No pathname expansion is performed on this command because double quotation marks suppress it. In the final command, the shell, without the limitations of quotation marks, performs variable substitution and then pathname expansion before passing the arguments to echo..

Process Substitution A special fe ature of the Bourne Again Shell is the ability to replace filename arguments with processes. An argument with the syntax <(command) causes command to be executed and the output written to a named pipe (FIFO). The shell replaces that argument with the name of the pipe.

If that argument is then used as the name of an input file during processing, the output of command is read. Similarly an argument with the syntax >(command) is replaced by the name of a pipe that command reads as standard input. The following example uses sort (pages 54 and 817) with the m (merge, which works correctly only if the input files are already sorted) option to combine two word lists into a single list.

Each word list is generated by a pipe that extracts words matching a pattern from a file and sorts the words in that list.. $ sort -m -f <(grep "[^A-Z]..$" memo1 sort) <(grep ".*aba.*" memo2 sort). Summary . The shell is Code 128B for Objective-C both a command interpreter and a programming language. As a command interpreter, it executes commands you enter in response to its prompt. As a programming language, the shell executes commands from files called shell scripts.

When you start a shell, it typically runs one or more startup files.. Running a shell script Assuming the iPhone barcode 128 file holding a shell script is in the working directory, there are three basic ways to execute the shell script from the command line. 1. Type the simple filename of the file that holds the script.

2. Type a relative pathname, including the simple filename preceded by ./.

3. Type bash or tcsh followed by the name of the file..

344 8 The Bourne Again Shell Technique 1 Code 128C for Objective-C requires that the working directory be in the PATH variable. Techniques 1 and 2 require that you have execute and read permission for the file holding the script. Technique 3 requires that you have read permission for the file holding the script.

. Job control A job is one code 128 barcode for Objective-C or more commands connected by pipes. You can bring a job running in the background into the foreground using the fg builtin. You can put a foreground job into the background using the bg builtin, provided that you first suspend the job by pressing the suspend key (typically CONTROL-Z).

Use the jobs builtin to see which jobs are running or suspended. The shell allows you to define variables. You can declare and initialize a variable by assigning a value to it; you can remove a variable declaration using unset.

Variables are local to a process unless they are exported using the export (bash) or setenv (tcsh) builtin to make them available to child processes. Variables you declare are called user-created variables. The shell defines keyword variables.

Within a shell script you can work with the command-line (positional) parameters the script was called with. Each process has a unique identification (PID) number and is the execution of a single Linux command. When you give it a command, the shell forks a new (child) process to execute the command, unless the command is built into the shell.

While the child process is running, the shell is in a state called sleep. By ending a command line with an ampersand (&), you can run a child process in the background and bypass the sleep state so that the shell prompt returns immediately after you press RETURN. Each command in a shell script forks a separate process, each of which may in turn fork other processes.

When a process terminates, it returns its exit status to its parent process. An exit status of zero signifies success; nonzero signifies failure. The history mechanism, a feature adapted from the C Shell, maintains a list of recently issued command lines, also called events, that provides a way to reexecute previous commands quickly.

There are several ways to work with the history list; one of the easiest is to use a command-line editor. When using an interactive Bourne Again Shell, you can edit a command line and commands from the history file, using either of the Bourne Again Shell s commandline editors (vim or emacs). When you use the vim command-line editor, you start in Input mode, unlike vim.

You can switch between Command and Input modes. The emacs editor is modeless and distinguishes commands from editor input by recognizing control characters as commands. An alias is a name that the shell translates into another name or (complex) command.

Aliases allow you to define new commands by substituting a string for the first token of a simple command. The Bourne Again and TC Shells use different syntaxes to define an alias, but aliases in both shells work similarly. A shell function is a series of commands that, unlike a shell script, is parsed prior to being stored in memory.

As a consequence shell functions run faster than shell scripts. Shell scripts are parsed at runtime and are stored on disk. A function can be defined on the command line or within a shell script.

If you want the function definition to remain in effect across login sessions, you can define it in a startup file..
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