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Drawer QR Code JIS X 0510 in Objective-C More Examples of Using Quoted Form

Earlier, you saw how to use quoted form to help you when writing shell scripts. This section goes a bit further into this subject, showing you some more practical examples of what you can do with it. Here s a simple example to show how to list the contents of a folder: do shell script "ls " & quoted form of POSIX path of the_folder The ls command is always a good one to experiment with because it s nondestructive and won t cause any damage if accidentally misused. You can take this further with a more potentially dangerous example involving your old friend rm: do shell script "rm -rf " & quoted form of POSIX path of the_file_or_folder

Although the do shell script command doesn t provide any way to feed data directly to standard input, you can supply standard input yourself in a couple of ways, each with its own advantages and disadvantages.

The simplest way to get data into a Unix application s standard input is to include it in the shell script. To do this, you use the echo application, which takes your input data as an argument (correctly quoted, of course!) and passes it directly to standard out. You can then use a pipe to redirect this output to the standard input of a second command.

To demonstrate, here s how you could use grep to find all lines in a linefeed-delimited string containing the specified pattern (also correctly quoted): do shell script "echo " & quoted form of input_text & " | grep " & quoted form of pattern_to_match For example, to find all the strings in a list that contain at least one digit (0 9), do this: set set set set the_list to {"hello", "bob42", "three", "0.197"} AppleScript's text item delimiters to (ASCII character 10) input_text to the_list as string pattern_to_match to "[[:digit:]]"

do shell script "echo " & quoted form of input_text & " | grep " & quoted form of pattern_to_match every paragraph of result --> {"bob42", "0.197"} This echo-based approach has a couple of disadvantages, however. The first is that the Unix shell sets a maximum length for scripts (on Tiger this is roughly 128KB), so if you try to pass too big a string, you ll get an error. The second is that if your string contains any ASCII 0 characters, you ll get an error because Unix often interprets ASCII 0 to mean end of string and will stop reading your shell script before it gets to the actual end. For some tasks these limitations won t be an issue, but when they are, you ll need to use the next approach.

Another way to get data from AppleScript to a Unix application s standard input is to write it to a temporary file and then redirect the shell script s standard input to read from that file. Although this approach takes a bit more work, it doesn t have the limitations of the echo-based approach you just saw. This approach has three steps. The first step is to create a suitable file path for writing the temporary file to. The second step is to write the temporary file using Standard Additions commands. The last step is to tell your shell script to read its standard input from this file. If you want, you can add some code that uses the rm command to erase the temporary file once it s no longer needed. This step isn t strictly necessary if you write the file to one of Mac OS X s temporary folders, however, because the Mac OS X will eventually clean up any leftovers in those locations for you. To keep the following example simple, I ve left out this cleanup stage, but you can add it if you want.