First off, the "cut" command does extract ONE field (or several fields, but this is advanced stuff you want to postpone until you grasped the basics) from a line consisting of several such fields. You really should read the man page of "cut". (Tip: if you want to extract several fields one at a time why don't you assign several variables one at a time?)
Secondly, you might want to think over the way you construct a while loop. Given, the way you do it works and it doesn't really make a difference in a 10-line-script, but you write this script to learn something so your concern should not only be to make it work but to learn the most possible from the exercise.
Consider this: when you feed data to a while-loop with a redirection at the end the script is becoming hard to read as the loop becomes longer. The following two loops do the same:
As long as the loop is short there is no problem, but if "...some processing..." consists of 100 lines: then you will start skipping backwards an forwards as you try to read the source code. Writing the input at top of the loop is somewhat easier to understand and therefore to maintain.
A third point: "read" is able to read several values at once - the values are delimited by the "IFS", the "internal field separator". This is the value the shell uses to separate input fields - even command arguments! Per default the IFS is a space character, which is why a line like "command arg1 arg2" will be interpreted as feeding two distinct arguments "arg1" and "arg2" to "command".
Lets do an exmple: Here is a input file, save this to "infile":
And here is some code to read this file, save it to a script "read_infile.sh" and execute it:
That leaves just the problem of changing the IFS to a colon instead of a space. Hint: you can assign it like any variable and example how to do this can be found in this forum, just use the search function.
There is even a fourth point: it pays to analyze what consumes (system) time on running a script. The most time consuming thing is forking new processes. Every time you invoke a command in a script a new process is started and this consumes time. You can read a very enlightening thread where i learned this lesson thanks to cfajohnson and perderabo here.
What does that mean for your script? Well, the line (i have corrected the syntactical error)
does something which can be done by "parameter expansion" too. Parameter expansion happens completely inside the shell and doesn't need its own process. Have a look at the man page of bash and search for "parameter expansion" to see what i mean.
Sorry for such a dreadful title, but I'm not sure how to be more descriptive. I'm hoping some of the more gurutastic out there can take a look at a solution I came up with to a problem, and advice if there are better ways to have gone about it.
To make a long story short around 20K pieces of... (2 Replies)
I'm trying to understand if it's possible to create a set of variables that are numbered based on another variable (using eval) in a loop, and then call on it before the loop ends.
As an example I've written a script called question (The fist command is to show what is the contents of the... (2 Replies)
Hi Im running this script, which is supposed to find the max value build some tables and then stop running once all the tables are built. Thing is , it keeps assigning a null value to $h and then $g is null so it keep building tables i.e. testupdateNUL. How can I stop this? Here is what I have:
... (4 Replies)
Hi all
Sorry for the basic question, but i am writing a shell script to get around a slightly flaky binary that ships with one of our servers. This particular utility randomly generates the correct information and could work first time or may work on the 12th or 100th attempt etc !.... (4 Replies)
Hi,
hope I am posting in the right section.
My problem is that I have 2 or more arguments passed and I want to check if the arguments passed exists or not.
The first argument should not exist and the remaining others should exist.
example:
./shells.sh argument1 argument2 argument3
... (5 Replies)
Hi, I was debating if I should put this in the dummies or scripts section, I apologize in advance if I chose poorly.
Fairly new to Unix and BASH scripting but I thought I made it fairly well given my limited understanding. However, the output indicates that it's looping and I'm ending up with a... (5 Replies)
Hello All,
Maybe I'm Missing something here but I have NOOO idea what the heck is going on with this....?
I have a Variable that contains a PATTERN of what I'm considering "Illegal Characters". So what I'm doing is looping
through a string containing some of these "Illegal Characters". Now... (5 Replies)
Hi,
I want to read file multiple times. Right now i am using while loop but that is not working.
ex.
While read line
do
while read line2
do
echo stmt1
#processing some data based on data.,
done < file2.txt
done < file1.txt # This will have 10... (4 Replies)
Hi all,
i developed a script to measure the uptime of a process in a Solaris 10/11 environments.
All is well, but i came across a situation where there are multiple processes of the same name. Basically i have the following result file:
beVWARS 13357 19592122
beVWARS 14329 19591910... (4 Replies)