It does not work that way. $(<file) is a special case, which is a faster alternative to $(cat file). If you are using anything other than just a file, it becomes something else. $( ... ) is just command sustitution, so if we leave out that, it becomes:
This is the same as tr -dc '[:alnum:],@#:!?+-' < /dev/urandom | head -c10
This is strange, it effectively just means cat /dev/urandom | head -c10
This is the same as the first one with UUOC
This is equivalent to :< /dev/urandom | tr -dc '[:alnum:],@#:!?+-' | head -c10, which is that same as : : | tr -dc '[:alnum:],@#:!?+-' | head -c10
This User Gave Thanks to Scrutinizer For This Post:
Can you use cat to send the first 25 lines of a file to the printer? I'm thinking I can pipe it with '|' but I'm not school to check printer output.
With the 'nl' used, all lines are numbered on the print out, but how does one number only the blank lines?
Thanks:) (1 Reply)
Hi,
I wnat to read a fiel line by line and store each line in a variabel, so I made a for loop:
for i in `cat file` ; do
#do sth.
done;
The problem is, that in the file, there are lines with only asterisks like this... (3 Replies)
Not sure how to do this exactly.. just want to take the first 100 lines of a file and cat it out into a second file. I know I can do a more on a file and > it into a different file, but how can I make it so only the first 100 lines get moved over? (1 Reply)
I want to cat a file with only show the line contain '/bin/bash' but don't show the line contain 'load' (don't show if the line contain 'load' and '/bin/bash' together), how to type in the command? thk a lot! (2 Replies)
I am looking for a command to take files with a specific date and cat them all into big file. I know I can use commands to list all of the files from a certain date. But I want to do that and take those files and make on large files containing all of them.
Any help would be great. This is being... (1 Reply)
Hi,
I have two files
one.txt
laptop
boy
apple
two.txt
unix
linux
OS
openS
I want to split one.txt into one line each and concatenate it with the two.txt
output files
onea.txt
laptop (4 Replies)
Hi All,
I have stumbled upon very unique issue. In my script I am doing cat file and then greping and cutting so as to assign the value to variable. My file is,
<mxc_tl_load_extractdata_prop.bsh>
DB_USER=test_oper
hostname=xxx
FTP_USER=test1_operate
MAIL_LIST=xxx@yyy.com... (1 Reply)
Hello,
I'm on a remote computer by SSH. How can I get the output of "cat file" into a file on the local computer?
I cannot use scp, because it's blocked.
something like:
ssh root@remote_maschine "cat /file" > /locale_machine/file
:rolleyes: (2 Replies)
Discussion started by: borsti007
2 Replies
LEARN ABOUT FREEBSD
pcap_get_selectable_fd
PCAP_GET_SELECTABLE_FD(3) Library Functions Manual PCAP_GET_SELECTABLE_FD(3)NAME
pcap_get_selectable_fd - get a file descriptor on which a select() can be done for a live capture
SYNOPSIS
#include <pcap/pcap.h>
int pcap_get_selectable_fd(pcap_t *p);
DESCRIPTION
pcap_get_selectable_fd() returns, on UNIX, a file descriptor number for a file descriptor on which one can do a select() or poll() to wait
for it to be possible to read packets without blocking, if such a descriptor exists, or -1, if no such descriptor exists. Some network
devices opened with pcap_create() and pcap_activate(), or with pcap_open_live(), do not support select() or poll() (for example, regular
network devices on FreeBSD 4.3 and 4.4, and Endace DAG devices), so -1 is returned for those devices.
Note that in:
FreeBSD prior to FreeBSD 4.6;
NetBSD prior to NetBSD 3.0;
OpenBSD prior to OpenBSD 2.4;
Mac OS X prior to Mac OS X 10.7;
select() and poll() do not work correctly on BPF devices; pcap_get_selectable_fd() will return a file descriptor on most of those versions
(the exceptions being FreeBSD 4.3 and 4.4), but a simple select() or poll() will not indicate that the descriptor is readable until a full
buffer's worth of packets is received, even if the read timeout expires before then. To work around this, an application that uses
select() or poll() to wait for packets to arrive must put the pcap_t in non-blocking mode, and must arrange that the select() or poll()
have a timeout less than or equal to the read timeout, and must try to read packets after that timeout expires, regardless of whether
select() or poll() indicated that the file descriptor for the pcap_t is ready to be read or not. (That workaround will not work in FreeBSD
4.3 and later; however, in FreeBSD 4.6 and later, select() and poll() work correctly on BPF devices, so the workaround isn't necessary,
although it does no harm.)
Note also that poll() doesn't work on character special files, including BPF devices, in Mac OS X 10.4 and 10.5, so, while select() can be
used on the descriptor returned by pcap_get_selectable_fd(), poll() cannot be used on it those versions of Mac OS X. Kqueues also don't
work on that descriptor. poll(), but not kqueues, work on that descriptor in Mac OS X releases prior to 10.4; poll() and kqueues work on
that descriptor in Mac OS X 10.6 and later.
pcap_get_selectable_fd() is not available on Windows.
RETURN VALUE
A selectable file descriptor is returned if one exists; otherwise, -1 is returned.
SEE ALSO pcap(3), select(2), poll(2)
22 July 2011 PCAP_GET_SELECTABLE_FD(3)