The main shell forks off a copy of itself to run while read independently of the echo so they can both run while connected by a pipe. The copy, or "sub-shell", runs successfully, setting all your variables and such as you please, until the pipe runs out of information and returns EOF. Then the loop quits.
Then the subshell dies. Control is returned to the main shell, which remains unchanged. You set all your variables in the subshell, not the main one.
In short: It's the pipe that does it. Your shell and everything behind the pipe are different processes and don't share variables.
Pipes are overkill if you have substring operators anyway. This way of getting a single character ought to work identically in bash and ksh:
Hi,
I have file abc.txt which has keys and emails addresses
abc.txt
emailkey1:sam@abc.com
emailkey1:tom@abc.com
emailkey2:rqw@abc.com
emailkey2:tut@abc.com
I have a shell script where i pass key as the parameter and i want all the email addresses within that key concatenated by a comma... (21 Replies)
I have a set of variables:
f1="./someFolder"
.
.
f10="./someOtherFolder"
And I'm trying to use the following loop
for (( i = 0; i <= 10; i++ ))
do
temp=f$i
done
I'm trying the get the values from my set of variable to make directories, but I can't seem the get those value... (3 Replies)
- I m retreving values from database and wish to use those values later in my shell script. I m placing these values in an array da_data but outside loop array is empty.Problem is its treating array as local inside loop hence array is empty outside loop.
Plz go through the script and suggest how... (1 Reply)
I need to do something like this:
for i in 1 2 3 4 5; do
arr=$(awk 'NR="$i" { print $2 }' file_with_5_records)
done
That is, parse a file and assign values to an array in an ascending order relative to the number of record in the file that is being processed on each loop.
Is my... (2 Replies)
I'm a programming noob. I'm trying to run a memory intensive process for many files. But when I use the following script, it runs fine for the first 5-7 files, then runs out of memory. Monitoring the output files, it's clear the processes are going on in parallel. Once 5-7 of the files are being... (18 Replies)
Hi All
I am trying to fetch the size of three files into three separate variables within a for loop and am doing something like this:
for i in ATT1 ATT2 ATT3
do
size_$i=`ls -ltr $i | awk '{print $5}'`
echo ${size_$i}
done
but am getting the below error:
ksh: size_ATT1=522: not... (3 Replies)
array=( 8 5 6 2 3 4 7 1 9 0 )
for i in "${array}"
do
echo $i
done
# i need the output like this by swapping of array values
0
9
1
7
4
3
2
6
5
8 (7 Replies)
I have a headerless array of 1000 columns x 100000 rows. The array only contains 4 values; 0/0, 0/1, 1/1, ./.
Here I am showing the 1st 3 rows and columns of the input array
0/0 0/0 1/1
0/1 0/1 0/1
0/0 ./. 0/0
0/0 0/0 0/0
I would like to convert the values in... (9 Replies)
Hello!
I'm making an English to Morse Code translator and I was able to mostly get it all working by looking through older posts here; however, I have one small problem.
When I run it it's just printing spaces for where the characters should be. It runs the right amount of times, and if I try... (3 Replies)
Discussion started by: arcoleman10
3 Replies
LEARN ABOUT ULTRIX
pipe
pipe(2) System Calls Manual pipe(2)Name
pipe - create an interprocess channel
Syntax
include <limits.h> /*Definition of PIPE_MAX*/
pipe(fildes)
int fildes[2];
Arguments
fildes Passing an address as an array of two integers into the system call.
Description
The system call creates an I/O mechanism called a pipe. The file descriptors returned can be used in and operations. Their integer values
will be the two lowest available at the time of the function call. The O_NONBLOCK and FD_CLOEXEC flags will be clear on both file descrip-
tors.
When the pipe is written using the descriptor fildes[1], up to PIPE_MAX bytes of data are buffered before the writing process is suspended.
A read using the descriptor fildes[0] picks up the data.
It is assumed that after the pipe has been set up, two (or more) cooperating processes (created by subsequent calls) pass data through the
pipe with and calls.
The shell has a syntax to set up a linear array of processes connected by pipes.
For further information on how and calls behave with pipes, see the and reference pages.
A signal is generated if a write on a pipe with only one end is attempted.
Restrictions
Should more than 4096 bytes be necessary in any pipe among a loop of processes, deadlock may occur.
The underlying implementation of pipes is no longer socket based, but rather implemented through the file system. Any application that
needs socket functionality from pipes should use the system call.
Return Values
The function value zero is returned if the pipe was created; -1 if an error occurred.
Diagnostics
The call fails if:
[EMFILE] Too many descriptors are active.
[ENFILE] The system file table is full.
[EFAULT] The fildes buffer is in an invalid area of the process's address space.
Environment
Differs from the System V definition in that ENFILE is not a possible error condition.
See Alsosh(1), fork(2), read(2), socketpair(2), write(2)pipe(2)