12-13-2007
Thanks Porter. I have calculated the offset from where I have to read. I believe before using lseek, I will have to open the file using open system call. I am getting a syntax error when I try to open the file. Please see code below:
apdma001:/amex/home/mqm/.saurabh # vi Myprog
"Myprog" 30 lines, 924 characters
# This is my first program
USAGE="Myprog <profile to be searched> "
if [ $# -ne 1 ]
then
echo "Invalid number of arguements :USAGE : $USAGE "
exit
fi
strToSearch="\."$1
# Write all relevant profiles into Myprog1. Filter those lines which have "MQQUEUE" so that only one occurance is listed
grep $strToSearch Sarah.txt | grep -v MQQUEUE > Myprog1
echo "Following profiles have been found:"
myfile="/amex/home/mqm/.saurabh/Myprog1"
myline=""
fd=open("Sarah.txt",O_RDONLY)
while [ 1 ]
do
read myline || break
# Remove "(G)" from the profile name
set -A profileNm $myline
# Search for second occurance of profileNm and read the line number of the second occurance
grep -n $profileNm Sarah.txt | head -n 2 | tail -n 1 | cut -f1 -d ":" | read startline
# Increase offset by 57 to move to access area
startline=`expr $startline + 57`
echo "$profileNm : $startline"
done < $myfile
Myprog[18]: 0403-057 Syntax error at line 18 : `(' is not expected.
I am new to unix, so my questions may appear very silly. But I am just trying to learn. Appreciate your help.
Thanks,
Saurabh
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lseek(2) System Calls Manual lseek(2)
Name
lseek, tell - move read or write pointer
Syntax
#include <sys/types.h>
#include <unistd.h>
pos = lseek(d, offset, whence)
off_t pos;
int d, whence;
off_t offset;
pos = tell(d)
off_t pos;
int d;
Description
The system call moves the file pointer associated with a file or device open for reading or writing.
The descriptor d refers to a file or device open for reading or writing. The system call sets the file pointer of d as follows:
o If whence is SEEK_SET, the pointer is set to offset bytes.
o If whence is SEEK_CUR the pointer is set to its current location plus offset.
o If whence is SEEK_END, the pointer is set to the size of the file plus offset.
Seeking beyond the end of a file and then writing to the file creates a gap or hole that does not occupy physical space and reads as zeros.
The system call returns the offset of the current byte relative to the beginning of the file associated with the file descriptor.
Environment
System Five
If you compile a program in the System Five environment, an invalid whence argument causes SIGSYS to be sent. This complies with the
behavior described in the System V Interface Definition (SVID), Issue 1.
Return Values
Upon successful completion, a long integer (the current file pointer value) is returned. This pointer is measured in bytes from the begin-
ning of the file, where the first byte is byte 0. (Note that some devices are incapable of seeking. The value of the pointer associated
with such a device is undefined.) If a value of -1 is returned, errno is set to indicate the error.
Diagnostics
The system call fails and the file pointer remains unchanged under the following conditions:
[EBADF] The fildes is not an open file descriptor.
[EINVAL] The whence is not a proper value.
[ESPIPE] The fildes is associated with a pipe or a socket.
See Also
dup(2), open(2)
lseek(2)