How do I compare two files in a shell script?
Here's my scenario. I have two files that have entries with each entry. 3-25 characters is the identifier. Based on this, I need to compare both of them and update the old file with the new file data if their IDs are the same. IDs start with 01. Take a look at the script below. This is giving some error as "the argument expected on line 12 that I cannot understand".
#!/bin/ksh
while read line
do
c=`echo $line|grep '^01' `
if [ $c -ne NULL ];
then
var=`echo $line|cut -c 3-25`
fi
while read i
do
d=`echo $i|grep '^01' `
if [ $d -ne NULL ];
then
var1=`echo $i|cut -c 3-25`
if [ $var -eq $var1 ];
then
$line=$i
fi
fi
done < test_monday
done < test_sunday
Please help me well in advance
Unless you are writing a script for portability of the original Bourne shell or others that do not support this feature, in Bash and ksh you should use the [[
test form for strings and files.
There is a reduced need for quoting and escaping, additional conditions such as pattern and regex matching, and the ability to use &&
and ||
instead of -a
and -o
.
if [[ $var == $var1 ]]
Also, "NULL" is not a special value in Bash and ksh, so your test will always succeed because it $d
tests for the literal string "NULL".
if [[ $d != "" ]]
or
if [[ $d ]]
For numeric values (not including leading zeros if you don't use octal), you can use numeric expressions. You can omit the dollar sign for variables in this context.
numval=41
if ((++numval >= 42)) # increment then test
then
echo "don't panic"
fi
No need to use echo
and cut
substring. In Bash and ksh, you can:
var=${line:3:23}
Note: cut
uses character positions for the start and end of a range, whereas this shell construct uses a start position and number of characters, so you need to adjust the numbers accordingly.
And it's a good idea to get away from using backticks . Use instead $()
. It can be nested and quoting and speeding up is shortened or simplified.
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