By "clear" I take it you mean that you want to truncate the file to zero size.
In that case...
Opening a file for writing (as opposed to appending) means you will overwrite anything in aready in the file, so writing zero-length data to the file leaves you with a zero-length file, wiping out out everything that was there.
e.g.
Hello,
I want to clear or modify a line of a file. It is possible by
cat filename | sed '3d'
for example. But If I want "3" to be a variable?
I can't do sed '$var d'
Help me please
Thank you very much (1 Reply)
Hai,
I have a program which updates the result in a log file, as the program runs 24*7,the size of log file keeps on increasing.
Can you help me with a shell command which will clear the content of a log file in use.
1) I tried tail -10 logfile > logfile ( the content is not changed )
2) >... (10 Replies)
I have a log file on our system which fills up with lines that have been timestamped, as follows....
03/03/2008 10:56:06:815] (ERROR) balance: continuing session to genapp02 : 18500
03/03/2008 10:56:06:820] (ERROR) balance: continuing session to genapp02 : 18500
03/03/2008 10:56:07:003]... (2 Replies)
Hello,
I have a script which creates a certain text file.
Whenever I call it, I need to recreate this file, because I have no need in the previous content.
So I thought to remove the file every time I call the script, and that way I am sure that the previous content will not interrupt me.... (2 Replies)
How can i print the output of a perl script on a unix console and redirect the same in a log file under same directory simultaneously ?
Like in Shell script, we use tee, is there anything in Perl or any other option ? (2 Replies)
Hi,
I have a script which will use an input.txt file as an input file.
I am providing data to this input file in the script and once the script is executed, I want to clear all the contents of this file as during the second time use of this script, I'll be appending the data in this input... (5 Replies)
proc get_view_rel_str { } {
set cc_view :] end]]
puts $cc_view
set a
puts $a
set a end]]
puts $a
set a
puts $a
set a
puts $a
set a
puts $a
}
get_view_rel_str
this is a script in tcl with clearcase view (1 Reply)
Hi,
I have a file with 15 fields seperated by '|'. The requirement is to clear the last 5 characters of the 14th field. modifications should be done to the original file .
Can some one help me in sorting this out. (2 Replies)
Discussion started by: sureshk_85
2 Replies
LEARN ABOUT FREEBSD
ftruncate
TRUNCATE(2) BSD System Calls Manual TRUNCATE(2)NAME
truncate, ftruncate -- truncate or extend a file to a specified length
LIBRARY
Standard C Library (libc, -lc)
SYNOPSIS
#include <unistd.h>
int
truncate(const char *path, off_t length);
int
ftruncate(int fd, off_t length);
DESCRIPTION
The truncate() system call causes the file named by path or referenced by fd to be truncated or extended to length bytes in size. If the
file was larger than this size, the extra data is lost. If the file was smaller than this size, it will be extended as if by writing bytes
with the value zero. With ftruncate(), the file must be open for writing.
RETURN VALUES
Upon successful completion, the value 0 is returned; otherwise the value -1 is returned and the global variable errno is set to indicate the
error. If the file to be modified is not a directory or a regular file, the truncate() call has no effect and returns the value 0.
ERRORS
The truncate() system call succeeds unless:
[ENOTDIR] A component of the path prefix is not a directory.
[ENAMETOOLONG] A component of a pathname exceeded 255 characters, or an entire path name exceeded 1023 characters.
[ENOENT] The named file does not exist.
[EACCES] Search permission is denied for a component of the path prefix.
[EACCES] The named file is not writable by the user.
[ELOOP] Too many symbolic links were encountered in translating the pathname.
[EPERM] The named file has its immutable or append-only flag set, see the chflags(2) manual page for more information.
[EISDIR] The named file is a directory.
[EROFS] The named file resides on a read-only file system.
[ETXTBSY] The file is a pure procedure (shared text) file that is being executed.
[EFBIG] The length argument was greater than the maximum file size.
[EINVAL] The length argument was less than 0.
[EIO] An I/O error occurred updating the inode.
[EFAULT] The path argument points outside the process's allocated address space.
The ftruncate() system call succeeds unless:
[EBADF] The fd argument is not a valid descriptor.
[EINVAL] The fd argument references a socket, not a file.
[EINVAL] The fd descriptor is not open for writing.
SEE ALSO chflags(2), open(2)HISTORY
The truncate() system call appeared in 4.2BSD.
BUGS
These calls should be generalized to allow ranges of bytes in a file to be discarded.
Use of truncate() to extend a file is not portable.
BSD December 13, 2006 BSD