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File io

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Pri Dhaka

This document discusses file and directory manipulation in Perl, including opening, reading from, and writing to files, as well as common file test operators. It also covers opening, reading from, and closing directories, rewinding the directory pointer, and changing, creating, and deleting directories.

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File/Directory manipulation
Opening a File To read from a file, must use a file handle. by convention, all caps open a file (for reading): open FILE, myfile.txt; open file for writing: open OUTFILE, >output.txt; open file for appending: open APPFILE, >>append.txt;
Reading from a file open FILE, myfile.txt; $one_line = <FILE>; @all_lines = <FILE>; @all_lines get all remaining lines from myfile.txt puts each line of file into one member of array remember chomp!
printing to a file open OUTFILE, >output.txt; print OUTFILE, Hello World!n; this can be tedious if all outputs are to same output file. select OUTFILE; make OUTFILE the default file handle for all print statements.
Close your files! open FILE, myfile.txt; @all_lines = <FILE>; close FILE; opening another file to the same filehandle will implicitly close the first one. dont rely on this. Its not Good Programming Practice.
File Test Operators Test to see if something is true about a file full list on page 98 of Prog. Perl. if (-e myfile.txt){ print file exists, now openingn; open FILE, myfile.txt; } can operate on filename or already existing filehandle
Directory manipulation directories can be opened, read, created, deleted, much like files. take care when doing these operations: youre affecting your directory structure many of the functions success will depend on what permissions you have on the specified directories.
open, read, close opendir DIR public_html; $nextfile = readdir DIR; @remaining_files = readdir DIR; closedir DIR;
Rewind opendir DIR .; $firstfile = readdir DIR; $secondfile = readdir DIR; rewinddir DIR; @allfiles = readdir DIR;
Change, Create, and Delete chdir change working directory. mkdir create directory (like unix call) rmdir remove directory (like unix call) works if and only if directory is empty chdir public_html; mkdir images rmdir temp;

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File io

  • 2. Opening a File To read from a file, must use a file handle. by convention, all caps open a file (for reading): open FILE, myfile.txt; open file for writing: open OUTFILE, >output.txt; open file for appending: open APPFILE, >>append.txt;
  • 3. Reading from a file open FILE, myfile.txt; $one_line = <FILE>; @all_lines = <FILE>; @all_lines get all remaining lines from myfile.txt puts each line of file into one member of array remember chomp!
  • 4. printing to a file open OUTFILE, >output.txt; print OUTFILE, Hello World!n; this can be tedious if all outputs are to same output file. select OUTFILE; make OUTFILE the default file handle for all print statements.
  • 5. Close your files! open FILE, myfile.txt; @all_lines = <FILE>; close FILE; opening another file to the same filehandle will implicitly close the first one. dont rely on this. Its not Good Programming Practice.
  • 6. File Test Operators Test to see if something is true about a file full list on page 98 of Prog. Perl. if (-e myfile.txt){ print file exists, now openingn; open FILE, myfile.txt; } can operate on filename or already existing filehandle
  • 7. Directory manipulation directories can be opened, read, created, deleted, much like files. take care when doing these operations: youre affecting your directory structure many of the functions success will depend on what permissions you have on the specified directories.
  • 8. open, read, close opendir DIR public_html; $nextfile = readdir DIR; @remaining_files = readdir DIR; closedir DIR;
  • 9. Rewind opendir DIR .; $firstfile = readdir DIR; $secondfile = readdir DIR; rewinddir DIR; @allfiles = readdir DIR;
  • 10. Change, Create, and Delete chdir change working directory. mkdir create directory (like unix call) rmdir remove directory (like unix call) works if and only if directory is empty chdir public_html; mkdir images rmdir temp;