Make a backup file: Difference between revisions
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→Tcl: Added implementation |
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=={{header|Tcl}}== |
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<lang tcl>package require Tcl 8.5 |
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proc backupopen {filename mode} { |
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set filename [file normalize $filename] |
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if {[file exists $filename]} { |
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set backups [glob -nocomplain -path $filename ,*] |
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set max [lindex [lsort -dictionary \ |
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[lsearch -all -inline -regexp $backups {,\d+$}]] end] |
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if {$max eq ""} { |
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set n 0 |
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} else { |
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set n [regexp -inline {\d+$} $max] |
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} |
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while 1 { |
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set backup $filename,[incr n] |
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if {![catch {file copy $filename $backup}]} { |
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break |
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} |
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} |
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} |
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return [open $filename $mode] |
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}</lang> |
}</lang> |
Revision as of 15:54, 11 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>
Tcl
<lang tcl>package require Tcl 8.5
proc backupopen {filename mode} {
set filename [file normalize $filename] if {[file exists $filename]} {
set backups [glob -nocomplain -path $filename ,*] set max [lindex [lsort -dictionary \ [lsearch -all -inline -regexp $backups {,\d+$}]] end] if {$max eq ""} { set n 0 } else { set n [regexp -inline {\d+$} $max] } while 1 { set backup $filename,[incr n] if {![catch {file copy $filename $backup}]} { break } }
} return [open $filename $mode]
}</lang>