Perl |打开和读取文件
文件句柄是一种内部 Perl 结构，它将物理文件与一个名称相关联。所有文件句柄都具有读/写访问权限，因此一旦文件句柄连接到文件，就可以进行读/写操作。但是，在关联文件句柄时，将指定打开文件句柄的模式。
Opening a File
打开功能用于打开新文件或现有文件。
语法:打开 FILEHANDLE，VAR
这里，FILEHANDLE 是打开函数返回的句柄，VAR 是具有文件名和打开文件模式的表达式。 下表显示了可以打开文件和访问各种操作的模式。 **r+9
| model | describe | | Or r < | Read-only access | | W or > | Create, write and truncate | | Or > > | Write, append and create |**
Reading a file
一旦一个 FILEHANDLE 被分配了一个文件，就可以进行读、写、追加等各种操作。读取文件有许多不同的方法。
- 使用文件句柄操作符
- 使用 getc 函数
-
使用读取功能
-
The FileHandle Operator The main method of reading the information from an open filehandle is using the operator < >. When < > operator is used in a list context, it returns a list of lines from the specified filehandle. The example below reads one line from the file and stores it in the scalar.
让文件“gfg . txt”的内容如下:
```perl GeeksforGeeks Hello Geek Geek a revolution Geeks are the best
```
例:GFG.pl
```perl
Opening the file
open(fh, "GFG.txt") or die "File '$filename' can't be opened";
Reading First line from the file
\(firstline = <fh>; print "\)firstline\n"; ```
输出:
-
getc Function The getc function returns a single character from the specified FILEHANDLE, or STDIN if none is specified
语法: getc FILEHANDLE
```perl
Opening the file
open(fh, "GFG.txt") or die "File '$filename' can't be opened";
Reading First char from the file
\(firstchar = getc(fh); print "\)firstchar\n"; ```
输出:
如果有错误或者文件句柄在文件的末尾，那么它返回 undef。
-
read Function The read function is used to read binary data from a file using filehandle.
语法 读取文件句柄，标量，长度，偏移量 读取文件句柄，标量，长度
这里，LENGTH 表示要读取的数据的长度，如果没有指定 OFFSET，数据将放在 SCALAR 的开头。否则，数据将被放在 SCALAR 中的 OFFSET 字节之后。文件读取成功后，函数返回读取的字节数，文件末尾为零，如果有错误，则返回 undef。
Reading Multiple line at a time
下面的例子读取文件句柄指定的文件内容，直到到达文件结尾(EOF)。
示例:File.pl
```perl
Opening the file
open(FH, "GFG.txt")or die "Sorry!! couldn't open"; print "Reading file \n";
Reading the file till FH reaches EOF
while(
) { # Printing one line at a time print $_; } close; ``` 输出:
Exception Handling in Files
异常有两种处理方式
- 如果文件无法打开，将引发异常
- 如果文件无法打开并继续运行，则发出警告
-
Throw an Exception When filehandle could not be assigned a valid file pointer at that time die gets executed printing the message and kills the current program. Example :
```perl
Initializing filename
$filename = 'GFG1.txt';
Prints an error and exits if file not found
open(fh, '<', $filename) or die "Couldn't Open file $filename"; ```
输出:
如果找不到文件，上面的代码会打印一个错误，并从代码中退出。
-
Give a warning When filehandle could not be assigned a valid file pointer it just prints warning message using warn function and keeps running. Example :
```perl
Initializing filename
$filename = 'GFG.txt';
Opening a file and reading content
if(open(fh, '<', $filename)) { while(
) { print $_; } } Executes if file not found
else { warn "Couldn't Open a file $filename"; } ```
输出:
