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Full Discussion: how to avoid 'unexpected operator' error when comparing 2 strings
Top Forums Shell Programming and Scripting how to avoid 'unexpected operator' error when comparing 2 strings Post 302443229 by agama on Saturday 7th of August 2010 04:35:01 PM
Old 08-07-2010
The test command is what is being invoked to process the expression between the square brackets. If either variable evaluates to nothing (in this case one of your files is empty), then the expression that the test command sees is:

Code:
    stuff =

(nothing trailing the operator if $c was empty) and this is not a legit expression.

Placing an 'x' in front of each variable ensures that the expression does not have any missing components, yet does not change the outcome of the string comparison because both strings will start with the same character.

Shells like Kshell which have a built-in test command (e.g. [[ $a == $b ]]) recognise an empty variable and do the right thing because the expression is being evaluated internally. So, in these scripts you will not encounter the 'x-trick' as it's not needed.

As for your method of cat'ing the files into variables might not be the most efficient way to accomplish your task. I'd use the diff command in this manner:

Code:
if diff -q file1 file2 >/dev/null 2>&1
then
    echo "match"
else
    echo "mismatch"
fi



---------- Post updated at 04:35 PM ---------- Previous update was at 04:29 PM ----------
Quote:
Originally Posted by methyl
Afaik the "==" is only valid in bash shell.
Yes, Bash and Kshell support the == operator, but only within their built-in test function ([[....]]). If a bash/Kshell script uses the single bracket command the contents in the expression are treated differently by the shell and the double equal operator is not valid.

Code:
#/usr/env/bin ksh
a=foo
b=bar
if [[ $a == $b ]]     # this is legit
then 
    echo true
else
    echo false
fi 

if [ $a == $b ]       # this will cause an error
then 
   echo true 
else
   echo false
fi

 

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LEARN ABOUT LINUX

gnomevfs-cat

gnomevfs-cat(1)                                                    User Commands                                                   gnomevfs-cat(1)

NAME

       gnomevfs-cat - print a file to standard output using the VFS system

SYNOPSIS

       gnomevfs-cat URI

DESCRIPTION

       gnomevfs-cat prints a file to standard output using the virtual file system to access the file via a URI.

OPERANDS

       The following operands are supported:

       URI             Specifies the file location in standard URI format.

EXAMPLES

       Example 1: Cat a File From a Web Server

       example% gnomevfs-cat http://www.sun.com

       Example 2: Cat a Local File

       example% gnomevfs-cat file:///home/user/README.txt

ENVIRONMENT VARIABLES

       See environ(5) for descriptions of the following environment variables: NLSPATH.

EXIT STATUS

       The exit value 0 is returned regardless of success or failure.

FILES

       The following files are used by this application:

       /usr/bin/gnomevfs-cat   Executable to print a file to standard output using the VFS system

ATTRIBUTES

       See attributes(5) for descriptions of the following attributes:

       +-----------------------------+-----------------------------+
       |      ATTRIBUTE TYPE         |      ATTRIBUTE VALUE        |
       +-----------------------------+-----------------------------+
       |Availability                 |SUNWgnome-vfs                |
       +-----------------------------+-----------------------------+
       |Interface stability          |External                     |
       +-----------------------------+-----------------------------+

SEE ALSO

       gnomevfs-copy(1), gnomevfs-info(1), gnomevfs-ls(1), gnomevfs-mkdir(1)

NOTES

       Written by Stephen Browne, Sun Microsystems Inc., 2004.

SunOS 5.10                                                          6 Sep 2004                                                     gnomevfs-cat(1)
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