Truncate a file: Difference between revisions
(Add UNIX Shell.) |
(unix: do not erase prior content in file) |
||
Line 50: | Line 50: | ||
=={{header|UNIX Shell}}== |
=={{header|UNIX Shell}}== |
||
<lang bash># Truncate a file named "myfile" to 1440 kilobytes. |
<lang bash># Truncate a file named "myfile" to 1440 kilobytes. |
||
truncate -s 1440k myfile</lang> |
|||
{{omit from|GUISS}} |
{{omit from|GUISS}} |
Revision as of 19:24, 19 July 2011
The task is to demonstrate how to truncate a file to a specific length. This should be implemented as a routine that takes two parameters: the filename and the required file length (in bytes). The truncation can be achieved using system or library calls intended for such a task, if such methods exist, or by creating a temporary file of a reduced size and renaming it, if no other method is possible. The file may contain non human readable binary data in an unspecified format, so the routine should be "binary safe", leaving the contents of the untruncated part of the file unchanged. If the specified filename does not exist, or the provided length is not less than the current file length, then the routine should raise an appropriate error condition and exit.
Java
The built-in function for truncating a file in Java will leave the file unchanged if the specified size is larger than the file. This version expects the source file name and the new size as command line arguments (in that order). <lang java>import java.io.FileOutputStream; import java.io.IOException; import java.nio.channels.FileChannel;
public class TruncFile { public static void main(String[] args) throws IOException{ if(args.length < 2){ System.out.println("Usage: java TruncFile fileName newSize"); return; } //turn on "append" so it doesn't clear the file FileChannel outChan = new FileOutputStream(args[0], true).getChannel(); int newSize = Integer.parseInt(args[1]); outChan.truncate(newSize); outChan.close(); } }</lang>
PureBasic
PureBasic has the internal function TruncateFile that cuts the file at the current file position and discards all data that follows. <lang PureBasic>Procedure SetFileSize(File$, length.q)
Protected fh, pos, i If FileSize(File$) < length Debug "File to small, is a directory or does not exist." ProcedureReturn #False Else fh = OpenFile(#PB_Any, File$) FileSeek(fh, length) TruncateFile(fh) CloseFile(fh) EndIf ProcedureReturn #True
EndProcedure</lang>
Ruby
This only works with some platforms. If truncation is not available, then Ruby raises NotImplementedError.
<lang ruby># Open a file for writing, and truncate it to 1234 bytes. File.open("file", "ab") { |f| f.truncate(1234) }
- Trunate a file to 567 bytes.
File.truncate("file", 567)</lang>
UNIX Shell
<lang bash># Truncate a file named "myfile" to 1440 kilobytes. truncate -s 1440k myfile</lang>