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Linux Script Variables

What Are Shell Script Variables?

A variable in a shell script is a means of referencing a numeric or character value. And unlike formal programming languages, a shell script doesn't require you to declare a type for your variables. Thus, you could assign a number to the variable stuff and then use it again in the same script to hold a string of characters. To access the value (contents) of a variable, prefix it with a dollar sign.

stuff=5
stuff='chocolate truffles'

Don't put any spaces before or after the equal sign, or you'll get an error. And if you want to assign a string that contains spaces, you will need to put quotation marks around the string.

This is a good time to note that there are several distinct ways to use quotations marks in a shell script. Let's look at the differences among single quotation marks, double quotation marks, and the backslash character and then follow up with some examples.

Single quotation marks, as in the preceding example, will always get you exactly what's inside the quotation marks--any characters that might otherwise have special meaning to the shell (like the dollar sign or the backslash) are treated literally.

Use double quotation marks when you want to assign a string that contains special characters the shell should act on.

The backslash is used to escape (treat literally) a single character (such as $ or *) that might otherwise be treated as a special character by the shell.

Now let's look at some examples that show when to use each method of quoting.

howdy='Good Morning $USER !'
echo $howdy

Good Morning $USER !

howdy="Good Morning $USER !"
echo $howdy
Good Morning hermie !

In the first case, the value of the howdy variable would probably not be what you wanted. The single quotation marks caused Bash to not treat $USER as a variable. In the second case, the results look much better. The double quotation marks allowed Bash to substitute the value of $USER, which is set automatically when you log in, in the string.

Here's another example that demonstrates a common error:

costmsg="Price is $5.00"
echo $costmsg
Actual result: Price is .00

We thought enough to quote the string, but the dollar sign tells Bash to use the value in the $5 variable, which is not what we wanted.. We can easily solve the problem by prefixing the dollar sign with a backslash, as shown here:

$ costmsg="Price is \$5.00"
$ echo $costmsg
Actual result: Price is $5.00

Arguments and Other Special Variables

Arguments are the values you pass to a shell script. Each value on the command line after the name of the script will be assigned to the special variables $1, $2, $3, and so on. The name of the currently running script is stored in the $0 variable.

Here are some other special variables you will find useful in script writing:

$# The number of arguments

$* The entire argument string

$? The return code from the last command issued

So let's try some examples working with arguments and other special variables. Create an executable script called testvars containing these lines:

echo "My name is $0"
echo "First arg is: $1"
echo "Second arg is: $2"
echo "I got a total of $# arguments."
echo "The full argument string was: $*"

Now if you run this script, here's what you'll see:

$ ./testvars birds have lips
My name is testvars
First arg is: birds
Second arg is: have
I got a total of 3 arguments.
The full argument string was: birds have lips

Previous Lesson: Executing a Script
Next Lesson: Shell Script Logic

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Comments - most recent first
(Please feel free to answer questions posted by others!)

Monica A R     (10 Jul 2014, 18:06)
I need to create a script file which fetches multiple database details one by one under single instance.(With username and password validation and fetch data accordingly using LOOPs)
Asit Adak     (26 Sep 2013, 05:05)
how to initialize variable in shell programming
Alan     (06 Apr 2013, 16:13)
This is a well done and informative guide, thank you very much for taking the time to post this!
vads     (16 Nov 2012, 06:42)
I used array to solve my below problem.
vads     (01 Nov 2012, 08:09)
I'm creating one small script. In this I'm taking numbers as user input. Now I want to assign each no. to different variable. Can anyone help how I can do this?

My script looks like below:
echo "Enter the no.s:"

Now I want to assign each no. to different variables.

For eg: If user inputs 35 56 85, then I need:
var1=35
var2=56
var3=85

Thanks in advance.



praveen     (16 Oct 2012, 07:42)
how to pass the value of one script to another script.

for example:

script1.sh

value1=90
value2=91
value3=93



script2.sh

echo $value1
echo $value2
echo $value3
if [ "$value1" -eq "$value2" ]; then
echo "$value1 is greater than $value2"
else
echo "$value1 is less than $value2"
vidhya     (15 Oct 2012, 04:40)
Hi I want to know how the output of a query can be stored in a variable using shell program
kvsr     (27 Aug 2012, 13:13)
Could you please explain below lines of script?
#-----------------
#including common.func file - common functions #are now available to be called from this script
. ${script_home}/common.func

. ${PROPERTIES} $1
tom     (18 Apr 2012, 02:06)
Hello,
I am new to Unix and have been tasked with:
Provided the following expression is used for adding two numbers in BASH:

`expr $1 + $2`

Develop a script that takes as input two numbers ($1, and $2), and adds the two numbers. If no input is provided, then exit with an error message.

I am stumped.I have been looking for hours. This expr has got me. Any and all help greatly appreciated
Ritika Pathak     (11 Apr 2012, 06:15)
i found amazing information in this........
its too good. keep it up......
Doug     (22 Mar 2012, 01:46)
How can a shell script tell which virtual console it is running on?

thanks
hari kishan     (18 Mar 2012, 12:05)
can you give a example in which the linux program take any real number
actually we want a program in linux ,in which the program take any n real value and give their sum average mini. & max value
but our program is taking only int. value . it is not taking desimal & negative value
the tast is not accept desimsal(2.3 etc.) value
Pushkraj     (16 Mar 2012, 05:20)
FTP_IP_ADD_1=10.10.10.10
FTP_IP_ADD_2=11.11.11.11
FTP_IP_ADD_3=12.12.12.12
TOTAL=3

count=0
while [[ $count -lt $TOTAL ]]
do
echo $count
count=$((count + 1))
ADDRESS=FTP_IP_ADD_$count
echo "$ADDRESS" #This will print FTP_IP_ADD_1,FTP_IP_ADD_2,FTP_IP_ADD_3
#(I want IP Address to be printed)
done
rakesh kumar rai     (05 Mar 2012, 13:13)
#!/bin/bash
echo 'date'
Sam     (17 Feb 2012, 23:02)
This does pertain to a homework assignment.I need to insert message @ startup and different one at shutdown inserting a soft link in the rc0.d and rc2.d directories I am pointing to a script with a case construct. I took the 1st few lines from other scripts in those files. I need to know where the $1 variable is getting it's value from. any help would be appreciated
yasaman     (17 Feb 2012, 07:14)
hi i am new in unix shell script..i need to create new item and edit the items for a supremarket.could u plz help me with that ?
amar nadh     (07 Feb 2012, 23:25)
sir, actually in a file it contains values like *103.172*
*10.3569* etc.
now i need get the data before the dot(.). for that i used cut command and tried to compare the cut value with dot(.). but it is showing error integer is expecting.
Bob Rankin     (04 Feb 2012, 18:52)
@CollZ - Did you just post your homework assignment, verbatim? LOL! :-)
CollZ     (04 Feb 2012, 01:31)
write a script that will ask the user an input and will determine the number of character inputs. the script should then print how many characters was entered by the user and will ask the if the user would start again or exit.
Muzaffar Hussain     (21 Jan 2012, 13:25)
Hi,

I am writing simple shell script i need to prefix the values of x and y with 'C'. Please advice.

#!/bin/bash
x=$(date +%Y%m%d)
echo $x

a=1
b=2
c=3
d=4
e=5
f=6

y= expr $x - $a
echo $y
Jon     (30 Sep 2011, 13:33)
I would greatly appreciate some Unix/Linux help with this. Running Fedora 14 and using BASH shell.

I have a situation where I need to refer to a variable that is "encapsulated" in single quotes ('). When I run the follwing, it does not recognize the variable. The value for name has to be surrounded by single quotes, otherwise it will yield errors. I've thought about using another value for the table entry, but all others are either too common or will not be known at the time this script is run. The program I am using to run this does not yield any errors.

query=$"`./query - @10.0.0.50 -d -a TABLE -w \"name: == '$DBPath'\" -s DELETE`"

echo $query

I have another command that adds data to the table that follows this same format, but there are no instances in that code where the variable is encapsulated in single quotes. Below:

post=$"`./mposter -n @10.0.0.50 -d -a TABLE -b \"name=$DBPath;description=Automated_Blackout_of_$DBPath;start=$StartDate;e nd=$EndDate`"
Mike     (11 Aug 2011, 08:47)
Attempting to name a file using a date variable but having issues appending to the end of the file name.
set DATEE=`date -d "yesterday" +"%m%d%y"`
cat file1.TXT file2.TXT file3.TXT > ${DATEE}newfile.txt
It works okay if I put the date varible at the end of newfile$DATEE.txt
Any help is appreciated.
hari     (29 Jun 2011, 15:16)
A shell variable cannont hold negative value ?
True or Flase?
Awais     (29 May 2011, 11:34)
ok so here is the problem:

lets say ive got the following string stored in mysql database in column 'info' of table 'TBL':

"ur name is $name"

and lets say ive got this code :
=================================================
#bin/bash
echo -n "enter your name: ";
read -e $name; /*read input from user an store it in $name*/

result=$(mysql -u USER -p -e "use xyz_db; select info from TBL where id=1;);

echo $result;

================================================

I want the string retrieved from database and stored in the variable "result", ("ur name is $name"), to be opened some how in this code so that the user supplied input of "$name" in this code be put in the variable "$name" of the retreived string from data base.

so when it asks: and a name is entered, like

enter your name: jhon

it should put that value in the string retrived from database which contains variable $name. and the out put should come as:

"ur name is jhon"
===============================================

its something that i need to do...and its getting very annoying. its my requirment that the string stored in the database should contain the variable that will store the input given by the user in the program.

I would REALLYY apriciate any bright ideas or ways or changes in this code to make this work.

best regard
Desperate_scripter
mahtab     (17 May 2011, 18:25)
please help me!
I am new in shell scripting. I have a lit of files like this:
BN090101
BN090102
.
.
BN090201
.
.
I want to read these file 1 by 1 and copy them to another directory. I mean copy for example first one then second one and so on. not all together. what should I do?
sahil     (02 Mar 2011, 07:53)
i want to compare decimal values in while loop condition.
plz help
malaz     (15 Feb 2011, 20:04)
I have a script that i am trying to display text content while the variable is part of for loop, Pretty much , I am trying to display string contents of equa_vma1, equa_vma2, .... using for loop
#!/bin/sh -x
equa_vma1="c0c1153a3024cf83-vma1"
equa_vma2="5a81153a3054cf83-vma2"
equa_vma3="c981153a3084cf83-vma3"
setup_80g ()
{
op=$1
initial=$2
max=$3
for i in $(seq $initial $max)
do
iqn="equa_vma$i"
echo $iqn
done
}
setup_80g a 1 2

malaz     (15 Feb 2011, 20:02)
I have a script that i am trying to display text content while the variable is part of for loop, Pretty much , I am trying to display string contents of equa_vma1, equa_vma2, .... using for loop
peter     (14 Feb 2011, 14:37)
Hello,
I am writing a script that reads a list of paths/directories and then enters each directory and create a folder with a name extracted from the name of this directory,
for example:
I have path to be ../gcm/peter
i have to get into ../gcm/peter and create a folder named shared_peter
here is my script (I need to change "shared" into shared_peter, which is part of $DIR):
#! /bin/sh
while read DIR
do
cd $DIR
echo "------------------------------------------------"
echo "I am in directory"
echo $DIR
echo "Creating shared directory"
mkdir -p shared
ls $DIR/
cd
echo "------------------------------------------------"
done

exit 0

thanks for the help
Dipankar Ghosh     (31 Jan 2011, 07:48)
hi i want to update a port number in a file such like......
file content.....abc.cfg

# Temporary use by Boyajian. Thank you.
# Plz feel free to change as per ur need. Thnx - Ayan
###---SBJ_VIEW_NAME=devB_4140sdd
#SBJ_VIEW_NAME=bagay_dev_mts_1440sdd
SBJ_VIEW_NAME=devD_4018
#SBJ_VIEW_NAME=devD_4017
ACE_MATCH_SERVER_HOST=localhost

ACE_MATCH_SERVER_PORT=16711

ACE_JASI_SERVER_PORT=75675
ENT_CLIENT_HOSTS=localhost,imts1,charon
ENT_SERVER_PORT=45785
ENT_SERVER_HOST=imts1
ENT_VIRTUAL_MEMORY=1000000000
ENT_NUM_ACCUMULATORS=8
SBJ_NO_SIG_CHECK=1
AREA_PROD_BRANCH=s2010


now if i want to update the value of ACE_MATCH_SERVER_PORT from 16711 to 78777
what would be the code to do this stub? please give a solution at the earliest

manoj     (08 Jan 2011, 23:23)
consider this and reply as early as possible
m=3
n=2
c=`expr $m / $n`
echo "$c"

this prints integer value
i need float value to be printed
pls help soon
jass     (24 Dec 2010, 09:01)
hi i am new for shell scropting and would like to learn it properly and i think this way i can learn fast.so please send me updates on shell scripting thanks.............
Dave     (19 Dec 2010, 17:21)
I am trying to write a script using nano that does the following: accepts three arguments and adds the numbers up
echo out the result

I am having no luck with this PLS HELP !!!
mejoo     (19 Nov 2010, 04:58)
very very very good
but,please disccusing the variable like
integer,float,double,and so on
"how work with it's"

thank you.
Edson     (29 Oct 2010, 14:17)
Hi, I need read Statement and search it's statement in a file of text. But just can read statement and don't can do the grep in the file.
This my config:
*********************************************
#!/bin/sh
# assign a value:
while :
do
clear
echo "-------------------------------------"
echo " Menu Principal "
echo "-------------------------------------"
echo "[1] Para verificar si esta configurado el mac"
echo "[2] Para verificar y agregar mac address"
echo "[3] Salir/Cancelar"
echo "======================="
echo -n "Entre su seleccion de [1-3]: "
read yourch
case $yourch in
1) echo "Introducir los 4 ultimos digitos del mac-address:" $fname
read $fname
echo "grep $fname /etc/vmps.dd" ;;
************************************************
But do nothing.
Ira     (14 Oct 2010, 16:37)
Bob,
I found the issue; the list "$*" should be "$@"

Works great.
Ira     (13 Oct 2010, 19:49)
I created this file named test:
for item in "$*"
do
echo "Argument value is: $item"
done

To run the file, I use:
./test a b c

The result I got was:

Argument value is: a b c
Why did the script put 'a b c' into one value?
Should I have seen:

Argument value is: a
Argument value is: b
Argument value is: c

Ben     (12 Oct 2010, 04:45)
THANKS :)
Steve     (03 Sep 2010, 17:47)
Thank you so much Bob Rankin. Your method worked and I didn't even have to write a script (I guess I was complicating the problem).
When running the program, the question format seems to be screwed up (all questions on one line? and the answers are blank?) but the programs results are correct so the fortran must have recognized the answers from the text file. Thanks again.
Bob Rankin     (03 Sep 2010, 09:47)
@Steve, Create a file named input.txt with each answer on a separate line, then run this command:

xx1 < input.txt
Steve     (02 Sep 2010, 20:01)
I have a fortran program that, when you run it, it asks the user for things (yes or no to questions, selection of options 1, 2, or 3). It asks 3 questions of the user and then based on the user responses, the program does things.

As an example, I run the program (called xx1):
>xx1
Do you want ascii output (y,n)?
>y
Do you want to use data1 (1) or data2 (2)?
>2
Do you want a pos plot (1) or a vel plot (2)?
>1
>

I want to record the answers for specific runs so I want to create a script where the answers are recorded and the script runs the program.

If I type on command line:
>xx1 y 2 1
this doesn't work.

How can I write a script to run xx1 with the answers to the questions in it, so I don't have to answer the questions each time?
windsor     (07 Aug 2010, 02:48)
I am trying to write a c shell script that takes a string as in pput and search in the current subdirectories.
In other words,
find . exec | grep "text to search for" '{}' \;

Called it myfind
find . exec | grep $1 '{}' \;

>myfind "text to search"
does not work
This does not work.
Michal     (03 Aug 2010, 13:31)
I am very new to the world of Linux and I am very confused with it. I have to write a script for a class and I have no idea how to start. I have an idea what commands to use, but putting it together is hard. The script is supposed to let an administrator know when a user has been accessing the system without permission. Can someone please help? Thanks
chinku     (27 Jul 2010, 16:31)
we generally use expr 2 + 3 to add two numbers can i change something to simply use it as 2 + 3 to get the output
NOYB     (13 Jul 2010, 17:29)
Special Variables, Arrays in FOR Loop

ARRAY=("ONE A Z" "TWO B Y" "THREE C X")

# for I in ${ARRAY[*]} # Each Item in the Array is listed.
# for I in ${ARRAY[@]} # Each Item in the Array is listed.
# for I in "${ARRAY[*]}" # Each String in the Array is Concatenated.
for I in "${ARRAY[@]}" # Each String in the Array is listed.
do
echo "LOOP START:"
echo $I
echo ${I[*]}
echo ${I[@]}
echo ${I[0]}

LOOP_ARRAY=($I)
echo LOOP ARRAY:
echo $LOOP_ARRAY # 1st Item of Loop Array
echo ${LOOP_ARRAY[0]} # 1st Item of Loop Array
echo ${LOOP_ARRAY[1]} # 2nd Item of Loop Array
echo ${LOOP_ARRAY[2]} # 3rd Item of Loop Array
done

jek     (17 May 2010, 19:37)
its not an error i want.. its the code for checking the error of a script.for example i have a script and i forgot to put an utility beside it to work.then the script containing the error command will check my other script that has an error and will prompt me to that.
Bob Rankin     (17 May 2010, 06:43)
What kind of errors do you want to find?
jek     (16 May 2010, 20:16)
i need a scrip which would determine a file with errors and would notify me that it has errors
Gyanu     (04 May 2010, 06:53)
Hi I am new for shell scripting and would like to learn it properly and I think this way I can learn fast. so please send me updates on Shell Scripting thanks
selva     (03 May 2010, 02:37)
good one, ive been following most of your tips on scripting. They are simple and easily uniderstandable...keep up the good work :)

cheers!!

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