Make a backup file: Difference between revisions
{{header|Common Lisp}} |
+Untested Java |
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Line 23: | Line 23: | ||
(with-standard-io-syntax |
(with-standard-io-syntax |
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(print data out)))))</lang> |
(print data out)))))</lang> |
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=={{header|Java}}== |
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{{untested|Java}} |
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{{works with|Java|7+}} |
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<lang java5>import java.io.PrintWriter; |
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import java.io.FileWriter; |
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import java.nio.file.*; |
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public class Backup { |
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public static void saveWithBackup(String filename, String... data){ |
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//toRealPath() follows symlinks to their ends |
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Path file = Paths.get(filename).toRealPath(); |
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Path back = Paths.get(filename + ".backup").toRealPath(); |
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Files.move(file, back, StandardCopyOption.REPLACE_EXISTING); |
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try(PrintWriter out = new PrintWriter(new FileWriter(file.toFile()))){ |
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for(String datum:data){ |
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out.println(datum); |
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} |
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} |
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} |
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}</lang> |
Revision as of 15:48, 10 November 2011
Before writing to a file it is often advisable to make a backup of the original. Creating such a backup file is however also not without pitfalls.
In this task you should create a backup file from an existing file and then write new text to the old file. The following issues should be handled:
- avoid making a copy of the file but instead rename the original and then write a new file with the original filename
- if a copy needs to be made, please explain why rename is not possible.
- keep in mind symlinks, and do not rename or copy the link but the target.
(if there is a link foo -> bar/baz
, then bar/baz
should be renamed to bar/baz.backup
and then the new text should be written to bar/baz
)
- it is assumed that you have permission to write in the target location, thus permission errors need not be handled.
- you may choose the backup filename per preference or given limitations.(it should somehow include the original filename however)
- please try to avoid executing external commands, and especially avoid calling a shell script.
Common Lisp
<lang lisp>(defun save-with-backup (filename data)
(let ((file (probe-file filename))) (rename-file file (concatenate 'string (file-namestring file) ",1")) (with-open-file (out file :direction :output :if-exists :supersede) (with-standard-io-syntax (print data out)))))</lang>
Java
<lang java5>import java.io.PrintWriter; import java.io.FileWriter; import java.nio.file.*;
public class Backup { public static void saveWithBackup(String filename, String... data){ //toRealPath() follows symlinks to their ends Path file = Paths.get(filename).toRealPath(); Path back = Paths.get(filename + ".backup").toRealPath(); Files.move(file, back, StandardCopyOption.REPLACE_EXISTING); try(PrintWriter out = new PrintWriter(new FileWriter(file.toFile()))){ for(String datum:data){ out.println(datum); } } } }</lang>