File handling

File Handling :

File names could be specified in Unix format.

In order to work with a file, first one has to open a channel to the file...this is also called handle

Once the channel is opened, TCL retruns a channelId which is used to work with the files

Typical steps to be followed while working with files:

Step 1: Check whether the file specified exists or not

Step 2: Open a channel pointing to the file...TCL returns an ID

Step 3: Use the ID to work with the file

Step 4: Close the channel after use

File Open :

"open" could be used to open a channel to a file. This command returns the file-handle (channelID) which could be used to work with the files.

Syntax:

open fileName ?access mode?

where

fileName - is the name of the file to be opened for use

access mode - either r, r+, w, w+, a or a+. These are the access modes (similar to C language)

"open" opens a channel to the file specified by the fileName with the access permissions specified by the access mode. Default is "r".

A channel once opened, remains open until specifically closed.

File Close :

"close" is used to close a channel previously opened using the "open" command.

Syntax:

close fileID

where

fileID - is the channel ID of the file opened

Example :

	set ofile [open data.txt w]
	for {set i 0 } { $i < 10 } { incr i } {
	puts $ofile "This is line number : $i "
	}
	close $ofile
	set ifile [open data.txt r]
	while { [gets $ifile line] != -1 } {
	puts $line
	}
	close $ifile

view raw file_operations.tcl hosted with ❤ by GitHub

some of the useful file operations are: (no need to open a channel for these operations)

file exists      --> checks if the specifie file exists or not

file dirname     --> returns the parent directory of the specified file

file extension   --> returns the extension (suffix) of the specified file (incl. dot)

file isfile      --> returns 1 if “name” is a normal file

file isdirectory --> returns 1 if “name” is a directory

file executable  --> returns 1 if “name” has executable permissions

file readable    --> returns 1 if “name” has read permissions

file writable    --> returns 1 if “name” has write permissions

file tail        --> returns the last pathname component of “name”

file rootname    --> returns all but the extension of the “name”