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Top Forums Shell Programming and Scripting Perl : How is file handling working here?? Post 302831881 by balajesuri on Friday 12th of July 2013 06:19:17 AM
Old 07-12-2013
Everytime you do read from a filehandle and store it in a scalar variable, then one line of input is read. (By one line, I mean the data until the next record separator).

Here is how it works internally:
When you open a filehandle, lets say, there's a mark that is at the beginning of file. The first time $rec = scalar <$INF> is encountered, the first line from file is read and referred by $rec. Now, the mark that we spoke of earlier, is at the character just after newline character (assuming newline as the default record separator). Now again when $rec = scalar <$INF> is encountered, one more line of data is read.

In the example code you provided in your post, a wrapper routine "readfile" reads one line of data and prints it.

The usual way of reading a file is to use a loop. Then again, that depends on what you really want to do:

Code:
open FH, "< /path/to/file";
while ($rec = <FH>) {
    print $rec;
}
close FH;

 

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split(n)						       Tcl Built-In Commands							  split(n)

__________________________________________________________________________________________________________________________________________________

NAME
split - Split a string into a proper Tcl list SYNOPSIS
split string ?splitChars? _________________________________________________________________ DESCRIPTION
Returns a list created by splitting string at each character that is in the splitChars argument. Each element of the result list will con- sist of the characters from string that lie between instances of the characters in splitChars. Empty list elements will be generated if string contains adjacent characters in splitChars, or if the first or last character of string is in splitChars. If splitChars is an empty string then each character of string becomes a separate element of the result list. SplitChars defaults to the standard white-space char- acters. EXAMPLES
Divide up a USENET group name into its hierarchical components: split "comp.lang.tcl.announce" . -> comp lang tcl announce See how the split command splits on every character in splitChars, which can result in information loss if you are not careful: split "alpha beta gamma" "temp" -> al {ha b} {} {a ga} {} a Extract the list words from a string that is not a well-formed list: split "Example with {unbalanced brace character" -> Example with {unbalanced brace character Split a string into its constituent characters split "Hello world" {} -> H e l l o { } w o r l d PARSING RECORD-ORIENTED FILES Parse a Unix /etc/passwd file, which consists of one entry per line, with each line consisting of a colon-separated list of fields: ## Read the file set fid [open /etc/passwd] set content [read $fid] close $fid ## Split into records on newlines set records [split $content " "] ## Iterate over the records foreach rec $records { ## Split into fields on colons set fields [split $rec ":"] ## Assign fields to variables and print some out... lassign $fields userName password uid grp longName homeDir shell puts "$longName uses [file tail $shell] for a login shell" } SEE ALSO
join(n), list(n), string(n) KEYWORDS
list, split, string Tcl split(n)
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