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Issues with 'expr'

 
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# 1  
Old 04-08-2013
Issues with 'expr'
Hi,

I have a text file where i define all the inputs to my shell script:
Code:
IP=1.2.3.4
PC=1234

In the shell script, i am trying to read the input variables from the above mentioned text file:

Code:
#!/bin/bash
#usage
IP=expr cat /tmp/input.txt | grep IP| cut -d "=" -f2
PC=expr cat /tmp/input.txt | grep PC | cut -d "=" -f2

echo "machine=$IP, PC=$PC"

But, i am getting the output as machine= , PC=

The correct values are not displayed
Last edited by Scrutinizer; 04-08-2013 at 03:27 AM.. Reason: code tags
# 2  
Old 04-08-2013
Quote:
Originally Posted by akarnya
#!/bin/bash
#usage
IP=expr cat /tmp/input.txt | grep IP| cut -d "=" -f2
PC=expr cat /tmp/input.txt | grep PC | cut -d "=" -f2

echo "machine=$IP, PC=$PC"
Why you need expr here..?

just use

Code:
IP=$(grep IP /tmp/input.txt | cut -d "=" -f2)
PC=$(grep PC /tmp/input.txt | cut -d "=" -f2)

This User Gave Thanks to pamu For This Post:
akarnya
# 3  
Old 04-08-2013
Thank you Smilie .. it works
# 4  
Old 04-08-2013
Why not source input.txt ?
Code:
source /tmp/input.txt
echo "machine=$IP, PC=$PC"

There are carriage returns in your input file. Convert to UNIX format first:
Code:
tr -d '\r' < infile > outfile

Last edited by Scrutinizer; 04-08-2013 at 03:38 AM..
# 5  
Old 04-08-2013
Quote:
Originally Posted by akarnya
Hi,

I have a text file where i define all the inputs to my shell script:
IP=1.2.3.4
PC=1234

In the shell script, i am trying to read the input variables from the above mentioned text file:

#!/bin/bash
#usage
IP=expr cat /tmp/input.txt | grep IP| cut -d "=" -f2
PC=expr cat /tmp/input.txt | grep PC | cut -d "=" -f2

echo "machine=$IP, PC=$PC"

But, i am getting the output as machine= , PC=

The correct values are not displayed
I'm very surprised that you didn't get diagnostic messages from your shell pointing out that expr cat /tmp/input.txt is a syntax error; the expr utility does not have a cat operator.
Change:
Code:
IP=expr cat /tmp/input.txt | grep IP| cut -d "=" -f2
PC=expr cat /tmp/input.txt | grep PC | cut -d "=" -f2

to:
Code:
. /tmp/input.txt

 
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