It's not a special case. Anywhere at all you have cat file | command, you can do command < file instead. You can even do so for entire shell statements, loops, and subshells the same way -- put the redirections on the end.
Code:
# This entire loop of code will have 'filename' as its standard input
while read LINE
do
...
done <filename
# This entire subshell will read from 'filename' as its standard input and write to 'outfile' as its standard output
# 'read' will read the first line. Then 'echo' will write 'something' into 'outfile'.
# Then 'grep' will hunt for 'word' in the rest of the file and print any results after 'something' in 'outfile'.
( read FIRSTLINE ; echo "something" ; grep "word" ) <filename >outfile
The special case is whether you could do command filename instead of command <filename. Whether that works depends entirely on the program you're giving the filename to.
This is one of the big differences between the Bourne shell and the C shell, incidentally. Bourne lets you put complicated redirections wherever it's convenient. C shell only lets you put very simple redirections, in very specific places.
Last edited by Corona688; 05-24-2012 at 03:27 PM..
Good morning - I have publication lists from 34 different faculty members. I need to end up with the numbers of publications in common across all 34 faculty.
I need to grep person1 (last name) in list2, person1 in list3, person1 in list 4, etc., then person2 in list3, person 2 in list4, etc.,... (2 Replies)
I have to to read files simultaneously in two nested loops,but am getting error can anyone do the needful.
useridFile=userIds.txt
fname=kiran.txt
exec<$useridFile
while read line
do
echo "User IDs are..$line"
USER_ID=$line
REMOTE_DIR_LOCATION="/home/test/$USER_ID"
SOURCE_DIR=$USER_ID... (1 Reply)
I need help getting over this bump on how nested for loops work in shell. Say i was comparing files in a directory in any other language my for loop would look like so
for(int i=0;to then end; i++)
for(int y = i+1; to the end; y++)
I can't seem to understand how i can translate that... (5 Replies)
You can use one while inside another?
I made the following script (without really knowing if I can use two while) to get 3 numbers different from each other at random:
num1=$(( $RANDOM % 10 ))
num2=$num1
while
do
num2=$(( $RANDOM % 10 ))
done
num3=$num1
while
do
while
do... (1 Reply)
Ok... am going slightly loopy trying to get this working (no pun intended)
What I need is to modify this code which takes a string input then echo's each character on a seperate line, to do the same thing but to put DIGIT: in front of numbers and LETTER: in front of letters.
I know a regular... (5 Replies)
KSH isn't my strong suit but it's what my company has to offer. I've got a script with two nested loops, a FOR and UNTIL, and that works fine. When I add a CASE into the mix I end up getting "Unexpected 'done' at line xx" errors. Any suggestions on this?
for divi in at ce ci cm co de di fl... (9 Replies)
Greetings All,
The following script attempts to enumerate all users in all groups in the group file(GROUP) and echo the following information:
GROUP ---> USER
The script is as follows:
IFS=","
for GROUP in `ypcat -k group | cut -d" " -f1`
do
for USER in `ypcat -k group... (13 Replies)
for server in $(echo `cat /tmp/ScanHosts_${USERSNAME}.TXT`)
do
for portnumber in $(echo `cat /tmp/ScanPorts_${USERSNAME}.TXT`)
do
#echo ${server} ${portnumber}
... (3 Replies)
Hi
A text file containing data something likeVehicle: BMW Class
checkin_note:
Tyre : Four
path_id : 11
vault_file_size: -1
Vehicle: Toyota Class
checkin_note:
Tyre : Four
path_id : 11
vault_file_size: -1
Vehicle: Chevrolet Class
checkin_note:
Tyre : Five
path_id :... (7 Replies)
Perl::Critic::Policy::ControlStructures::ProhibitDeepNesUserpContributed Perl DocumPerl::Critic::Policy::ControlStructures::ProhibitDeepNests(3pm)NAME
Perl::Critic::Policy::ControlStructures::ProhibitDeepNests - Don't write deeply nested loops and conditionals.
AFFILIATION
This Policy is part of the core Perl::Critic distribution.
DESCRIPTION
Deeply nested code is often hard to understand and may be a sign that it needs to be refactored. There are several good books on how to
refactor code. I like Martin Fowler's "Refactoring: Improving The Design of Existing Code".
CONFIGURATION
The maximum number of nested control structures can be configured via a value for "max_nests" in a .perlcriticrc file. Each for-loop, if-
else, while, and until block is counted as one nest. Postfix forms of these constructs are not counted. The default maximum is 5.
Customization in a .perlcriticrc file looks like this:
[ControlStructures::ProhibitDeepNests]
max_nests = 3
AUTHOR
Jeffrey Ryan Thalhammer <jeff@imaginative-software.com>
COPYRIGHT
Copyright (c) 2005-2011 Imaginative Software Systems. All rights reserved.
This program is free software; you can redistribute it and/or modify it under the same terms as Perl itself. The full text of this license
can be found in the LICENSE file included with this module.
perl v5.14.2 2012-06-07 Perl::Critic::Policy::ControlStructures::ProhibitDeepNests(3pm)
05-24-2012
Anywhere at all you have cat file | command, you can do command < file instead. You can even do so for entire shell statements, loops, and subshells the same way -- put the redirections on the end.