Question

I’m writing a script to find out the diff between files using the GNU version of the diff command. Here I need to ignore the html comment <!– and any patterns (provided as input through a file) that is matched.

File wxy/a:

<?xml version="1.0" encoding="UTF-8"?>
<beans xmlns="http://www.springframework.org/schema/beans"
       xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
       xmlns:p="http://www.springframework.org/schema/p"
       xsi:schemaLocation="http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans-2.0.xsd">
some text here
           <property name="loginUrl" value="http://localhost:15040/ab/ssoLogin"/>
     <!--property name="cUrl" value="http://localhost:15040/ab/ssoLogin" /-->
</beans>

File xyz/a:

<?xml version="1.0" encoding="UTF-8"?>
<beans xmlns="http://www.springframework.org/schema/beans"
       xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
       xmlns:p="http://www.springframework.org/schema/p"
       xsi:schemaLocation="http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans-2.0.xsd">
some text there
           <property name="loginUrl" value="http://localhost:15045/ab/ssoLogin"/>
     <!--property name="cUrl" value="http://localhost:15045/ab/ssoLogin" /-->
</beans>

Pattern input file: input.conf:

[a]
http://.*[:0-9]*/ab/ssoLogin
[some other file]
....
....

My script would read the input.conf for the filename [a] and puts to a temp file lines_to_ignore, now I read the file lines_to_ignore and append the pattern to a variable like below

compare_file.sh

diff_ignore_options="-I \"\!--\"" # Ignore option for <!-- Comments

for iline in `cat lines_to_ignore`; do
    diff_ignore_options=${diff_ignore_options}" -I \"$iline\""
    echo "-----------------------------------------------------------"
    diff -I "\!--" -I "$iline" wxy/a xyz/a
    echo "-----------------------------------------------------------"
done

diff $diff_ignore_options wxy/a xyz/a 

Now the output:

-----------------------------------------------------------
19c19
< some text here
---
> some text there
-----------------------------------------------------------

19,21c19,21
< some text here
<            <property name="loginUrl" value="http://localhost:15040/ab/ssoLogin"/>
<      <!--property name="cUrl" value="http://localhost:15040/ab/ssoLogin" /-->
---
> some text there
>            <property name="loginUrl" value="http://localhost:15045/ab/ssoLogin"/>
>      <!--property name="cUrl" value="http://localhost:15045/ab/ssoLogin" /-->

Why is the variable substitution in diff command not working?

diff $diff_ignore_options wxy/a xyz/a

I want to do it the variable way because I might have to match more than one pattern in some files.

Answer 1

The problem is the ! character, which the shell uses for history expansion. Furthermore, you’re including escaped double-quote characters in your $diff_ignore_options variable; since the pattern you want to ignore doesn’t include any " characters, you don’t want that.

This should work (note the use of single quotes to avoid treating ! as a metacharacter):

diff_ignore_options='-I !--'
diff $diff_ignore_options this_file that_file

And you can then add more patterns like this:

diff_ignore_options="$diff_ignore_options -I foobar"