File Handling:
As in all other good languages, Tcl also can open, read and
write to files. And like all other good tutorials, this tutorial also teaches
how to do it. First let us see how to open a file.
fileName is the name of the file. The access argument, if
present, specifies the way in which the file should be accessed. It can have
any of the following values:
File modes:
r == Open the file for reading only; the file must already
exist.
This is the default value if access is not specified.
r+ == Open the file for both reading and writing; the file must
already exist.
w == Open the file for writing only. Truncate it if it exists.
If it doesn't exist, create a new file.
w+ == Open the file for reading and writing. Truncate it if it
exists.
If it doesn't exist, create a new file.
a == Open the file for writing only. The file must already
exist, and the file is positioned
so that new data is appended to the file.
a+ == Open the file for reading and writing. If the file doesn't
exist, create a new empty file.
Set the initial access position to the end of
the file.
In TCl , by default stdout is output channel id.
Lets see an example.
#Open the file called "jokes.txt" for writing
open "jokes.txt" w
Now we know how to open a file. Not much good, is it? To make
this function useful, we need to write to the file.
puts
Syntax:
puts ?-nonewline? ?channelId? string
Use the -nonewline option only if you don't need a new line at
the end of the string you write to a file. The channelID stands for the ID of
the output stream that must be written to(if you don't understand what the
means, don't worry. You will get it latter.) string is the string you want to
write to the file. Lets see the example.
#Open the file called "jokes.txt" for writing
set out [open "jokes.txt" w]
puts $out "Computers make very fast, very accurate
mistakes."
Notice that I created a variable called 'out'. That will store
the ID of the opened file. Always open a file in this way - otherwise they
won't be of much use. Then we use that ID to write to the file using the
command 'puts'. Now the file called "jokes.txt" has one line. Next we
have to close the file.
close
Syntax:
close ?channelId?
close $out
This command closes the channel. Always do this - else you will
cry later. Lets move on to the ever growing example...
#Open the file called "jokes.txt" for writing
set out [open "jokes.txt" w]
puts $out "Computers make very fast, very accurate
mistakes."
close $out
After we close the file, we decide that we have to put more
lines in the file. So now we open the file again, this time in the append mode.
The example grows even longer...
#Open the file called "jokes.txt" for writing
set out [open "jokes.txt" w]
puts $out "Computers make very fast, very accurate
mistakes."
close $out
set out [open "jokes.txt" a]
puts $out "Computers are not intelligent. They only think
they are."
puts $out "My software never has bugs. It just develops
random features."
puts $out {All computers wait at the same speed.
Best file compression around: "DEL *.*" = 100%
compression
DEFINITION: Computer - A device designed to speed and automate
errors.
DEFINITION: Upgrade - Take old bugs out, put new ones in.}
close $out
After we have done that, we need to read the jokes and put them
back on the screen. So we learn a new command. Ladies and Gentlemen let me
introduce you to...
gets
Syntax:
gets channelId ?varName?
gets will copy one line from the channel(or file) and put it in
varName. If varName is not specified, the copied line will be the result of the
function. We go back to our example and get the first line of the file. For
that we open the file again, this time in read mode.
#Open the file called "jokes.txt" for writing
set out [open "jokes.txt" w]
puts $out "Computers make very fast, very accurate
mistakes."
close $out
#Now append more jokes at the end of the file
set out [open "jokes.txt" a]
puts $out "Computers are not intelligent. They only think
they are."
puts $out "My software never has bugs. It just develops
random features."
puts $out {All computers wait at the same speed.
Best file compression around: "DEL *.*" = 100%
compression
DEFINITION: Computer - A device designed to speed and automate
errors.
DEFINITION: Upgrade - Take old bugs out, put new ones in.}
close $out
#Opening file in read mode
set in [open "jokes.txt" r]
gets $in line
label .line -text "First Line : $line"
pack .line
This command can be used to read the whole file line by line.
See the example below to see how. Don't worry about .txt insert end
"$line\n---\n" - I will explain it later.
text .txt
set in [open "Jokes.txt" r]
while {[gets $in line] != -1} {
#Do whatever you want with the $line variable
.txt insert end "$line\n---\n"
}
close $in
pack .txt -expand 1 -fill both
This command is for reading the file line by line. Now we decide
that we need to see the entire file. For that we need the read command. But
remember that if we have read one line before, the read command will read only
from the second line. For resetting the channel to the first position, we need
the seek command.
seek
Syntax:
seek channelId offset ?origin?
The offset and origin arguments specify the position at which
the next read or write will occur for channelId. Offset must be an integer
(which may be negative) and origin must be one of the following - start,
current or end.
Now we have to read the file contents. So we move on to...
read
Syntax:
read channelId ?numChars?
read will take numChars characters from the channel and return
it. If numChars is not specified, the whole file is read and its content will
be returned. You can read a file and then get all the lines into a list with
every line as an item in the list. This can be done by...
set in [open "file.txt" r]
set contents [read $in]
close $in
set lines [split $contents "\n"]
Now every item in the list called $lines is a line of the file
called "file.txt". On to the example - for the last time.
#Open the file called "jokes.txt" for writing
set out [open "jokes.txt" w]
puts $out "Computers make very fast, very accurate
mistakes."
close $out
#Now append more jokes at the end of the file
set out [open "jokes.txt" a]
puts $out "Computers are not intelligent. They only think
they are."
puts $out "My software never has bugs. It just develops
random features."
puts $out {All computers wait at the same speed.
Best file compression around: "DEL *.*" = 100%
compression
DEFINITION: Computer - A device designed to speed and automate
errors.
DEFINITION: Upgrade - Take old bugs out, put new ones in.}
close $out
#Opening file in read mode
set in [open "jokes.txt" r]
gets $in line
label .line -text "First Line : $line"
pack .line
seek $in 0 start
set contents [read $in]
close $in
label .full -text "Full file Contents... \n$contents"
pack .full
There. That's about it with file handling.
-------------------------
How do I read and write files in Tcl
One way to get file data in Tcl is to 'slurp' up the file into a
text variable. This works really well if the files are known to be small.
# Slurp up the data file
set fp [open "somefile.txt" r]
set file_data [read $fp]
close $fp
Now you can split file_data into lines, and process it to your
heart's content. NOTE: The mention of split is important here- input data is
seldom well-behaved/structured, and needs to be processed in this way to ensure
that any potential Tcl metacharacters are appropriately quoted into list
format.
# Process data file
set data [split $file_data "\n"]
foreach line $data {
# do some line processing
here
}
# read the file one line at a time
set fp [open "somefile.txt" r]
while { [gets $fp data] >= 0 } {
puts $data
}
close $fp
#Writing a file
# create some data
set data "This is some test
data.\n"
# pick a filename - if you don't
include a path,
# it will be saved in the
current directory
set filename
"test.txt"
# open the filename for writing
set fileId [open $filename "w"]
# send the data to the file -
# failure to add '-nonewline'
will result in an extra newline
# at the end of the file
puts -nonewline $fileId $data
# close the file, ensuring the data
is written out before you continue
# with processing.
close $fileId
set searcrhResults {dir1/dir2/dir3/file1.tcl dir1/dir3/file1.tcl dir1/dir2/file1.tcl dir1/dir2/dir3/file2.tcl dir1/dir2/dir3/file3.tcl dir1/dir3/file2.tcl dir1/file3.tcl dir1/file4.tcl }
foreach file $searcrhResults {
if {[catch {incr filenames([file tail $file],cnt)}]} {
set filenames([file tail $file],cnt) 1
}
lappend filenames([file tail $file],paths) [file dirname $file]
}
#append
#Open the file called "jokes.txt" for writing
set out [open "jokes.txt" w]
puts $out "Computers make very fast, very accurate mistakes."
close $out
#Now append more jokes at the end of the file
set out [open "jokes.txt" a]
puts $out "Computers are not intelligent. They only think they are."
puts $out "My software never has bugs. It just develops random features."
puts $out {All computers wait at the same speed.
Best file compression around: "DEL *.*" = 100% compression
DEFINITION: Computer - A device designed to speed and automate errors.
DEFINITION: Upgrade - Take old bugs out, put new ones in.}
close $out
Read :
set fp [open "somefile.txt" r]
set file_data [read $fp]
close $fp
set fp [open "somefile.txt" r+]
set file_data [read $fp]
set data "hello how r u"
puts $fp $data
close $fp
Now if u open a file ..vi somefile.txt ..hello how r u --will be added
Write:
# create some data
set data "This is some test data.\n"
# pick a filename - if you don't include a path,it will be saved in the current directory
set filename "test.txt"
# open the filename for writing
set fileId [open $filename "w"]
# send the data to the file - failure to add '-nonewline' will result in an extra
newline
# at the end of the file
puts -nonewline $fileId $data
# close the file, ensuring the data is written out before you
continue with processing.
close $fileId
#FILE
CONCEPTS & explain me regsub with example.
set fW [open write w]
puts $fW "MY FIRST LINE"
puts $fW "My Second Line"
close $fW
set fR [open write r]
set content [read $fR]
puts $content
#now
regsub -nocase -all "my" $content
"Our" content
puts $content
close $fR
OUTPUT:
MY FIRST LINE
My Second Line
Our FIRST LINE
Our Second Line
##File
operations print the contents of a file and next make multiple lines of a file
to single line in that file
set fp [open shiva w]
puts $fp "Hi My name is shiva"
puts $fp "I am workig in wipro"
close $fp
set fp [open shiva r]
set contents [read $fp]
close $fp
set contents [split $contents "\n"]
set fp [open shiva w]
foreach line $contents {
append new $line
}
puts $fp $new
close $fp
set fp [open shiva r]
set cnt [read $fp]
puts $cnt
OUPUT:
Hi My name is shiva
I am workig in wipro
Hi My name is shivaI am workig in wipro
No comments:
Post a Comment
Note: only a member of this blog may post a comment.