when I try to redirect input and the command is described as a string within an array redirection does not work. why?
dir=("tail < ./hello.txt") is the equivalent of dir="tail < ./hello.txt"
You are assigning a string to a variable.
echo $dir will show you the string tail < ./hello.txt and not the execution of the command.
By the way, you do not need redirection. tail can read from the file without extra help as tail hello.txt
dir=$(tail hello.txt) will assign the result of executing the command into the variable dir.
That will evaluate the string tail hello.txt as a command.
Therefore, eval ${dir[0]} will do the same.
Hi everybody, first of all i am a new member in UNIX.com and this is my first post.
I am impressed with the amount of information a person can ever have in this forum, it is really great having something similiar; anyways let me tell you about the problem I am having, hope you will answer me.... (6 Replies)
Hi,
in my script I need to execute the following command:
query $id 456 432
but it waits for a RETURN character from keyboard and therefore, it fails. I tried something like:
query $id 456 432 << '\n'
but, i'ts clear it is not correct. Is there any way to do this?
Thxs. (0 Replies)
Hello,
I need to change user and run some commands by using a script.
lets say, I'm using
su - someuser << start
password required -----> how can I enter the password here
command 1
command 2
command 3
command 4
start
While trying to run this I got the following message:
"standard... (2 Replies)
Hello,
I need help with a bash script that I try to improve. I could not find answer so far, maybe because I'm not to familiar with the terminology so feel free to correct my language.
I have a script that looks like:
NODES="node_a node_b node_c"
for NODE in $NODES
do
... (4 Replies)
All,
I have a requirement to write a script where I check for Input redirection when the script was executed, based on which I handle my logic. Below is the example:
my.script
#! /bin/ksh
# Not sure how to frame the if condition below
if ; then
echo "Input Redirected from a file"
... (7 Replies)
Hello everyone,
My requirement is that within a script I need to construct the command line exactly that it was invoked with. For example :
sh a.sh arg1 arg2 arg3 < input.txt > output.txt
Now within a.sh, I construct a file which has these contents "
sh a.sh arg1 arg2 arg3 < input.txt >... (8 Replies)
Hello,
I'm new to Unix (working with OS X 10.8.5) and therefore at the beginning of my adventure. If I ask something stupid, then this is not intentional, but simple nescience. :rolleyes:
I have a problem with the redirection of text file content to echo. I was experimenting with redirection... (6 Replies)
Can someone please explain when input redirection is necessary?
For example, "cat filename" and "cat< filename" produce the same result. I was told that if I need to bunzip a file that I should type "bunzip2<filename.bz2." However, if I omit the "<" I still get the same result. Can someone... (4 Replies)
Hi,
#!/bin/bash
while ;
do
rm -f /tmp/pipe
mkfifo /tmp/pipe
./yuv4mpeg_to_v4l2 < /tmp/pipe &
mplayer tom_and_jerry.mp4 -vf scale=480:360 -vo yuv4mpeg:file=/tmp/pipe
sleep 65;
done
When I run this - after mplayer finishes playing video it says - Exiting... (End of... (2 Replies)
Discussion started by: ashokvpp
2 Replies
LEARN ABOUT PLAN9
tail
TAIL(1) General Commands Manual TAIL(1)NAME
tail - deliver the last part of a file
SYNOPSIS
tail [ +-number[lbc][rf] ] [ file ]
tail [ -fr ] [ -n nlines ] [ -c ncharacters ] [ file ]
DESCRIPTION
Tail copies the named file to the standard output beginning at a designated place. If no file is named, the standard input is copied.
Copying begins at position +number measured from the beginning, or -number from the end of the input. Number is counted in lines, 1K
blocks or characters, according to the appended flag or Default is -10l (ten ell).
The further flag causes tail to print lines from the end of the file in reverse order; (follow) causes tail, after printing to the end, to
keep watch and print further data as it appears.
The second syntax is that promulgated by POSIX, where the numbers rather than the options are signed.
EXAMPLES
tail file
Print the last 10 lines of a file.
tail +0f file
Print a file, and continue to watch data accumulate as it grows.
sed 10q file
Print the first 10 lines of a file.
SOURCE
/sys/src/cmd/tail.c
BUGS
Tails relative to the end of the file are treasured up in a buffer, and thus are limited in length.
According to custom, option +number counts lines from 1, and counts blocks and characters from 0.
TAIL(1)