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)
Discussion started by: vipinHasija
7 Replies
LEARN ABOUT HPUX
source
exec(1) User Commands exec(1)NAME
exec, eval, source - shell built-in functions to execute other commands
SYNOPSIS
sh
exec [argument...]
eval [argument...]
csh
exec command
eval argument...
source [-h] name
ksh
*exec [arg...]
*eval [arg...]
DESCRIPTION
sh
The exec command specified by the arguments is executed in place of this shell without creating a new process. Input/output arguments may
appear and, if no other arguments are given, cause the shell input/output to be modified.
The arguments to the eval built-in are read as input to the shell and the resulting command(s) executed.
csh
exec executes command in place of the current shell, which terminates.
eval reads its arguments as input to the shell and executes the resulting command(s). This is usually used to execute commands generated as
the result of command or variable substitution.
source reads commands from name. source commands may be nested, but if they are nested too deeply the shell may run out of file descrip-
tors. An error in a sourced file at any level terminates all nested source commands.
-h Place commands from the file name on the history list without executing them.
ksh
With the exec built-in, if arg is given, the command specified by the arguments is executed in place of this shell without creating a new
process. Input/output arguments may appear and affect the current process. If no arguments are given the effect of this command is to mod-
ify file descriptors as prescribed by the input/output redirection list. In this case, any file descriptor numbers greater than 2 that are
opened with this mechanism are closed when invoking another program.
The arguments to eval are read as input to the shell and the resulting command(s) executed.
On this man page, ksh(1) commands that are preceded by one or two * (asterisks) are treated specially in the following ways:
1. Variable assignment lists preceding the command remain in effect when the command completes.
2. I/O redirections are processed after variable assignments.
3. Errors cause a script that contains them to abort.
4. Words, following a command preceded by ** that are in the format of a variable assignment, are expanded with the same rules as a vari-
able assignment. This means that tilde substitution is performed after the = sign and word splitting and file name generation are not
performed.
EXIT STATUS
For ksh:
If command is not found, the exit status is 127. If command is found, but is not an executable utility, the exit status is 126. If a redi-
rection error occurs, the shell exits with a value in the range 1-125. Otherwise, exec returns a zero exit status.
ATTRIBUTES
See attributes(5) for descriptions of the following attributes:
+-----------------------------+-----------------------------+
| ATTRIBUTE TYPE | ATTRIBUTE VALUE |
+-----------------------------+-----------------------------+
|Availability |SUNWcsu |
+-----------------------------+-----------------------------+
SEE ALSO csh(1), ksh(1), sh(1), attributes(5)SunOS 5.10 17 Jul 2002 exec(1)
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.