Thread: Why doesn't this work?

I'm writing a simple script to change the file extension of a file. I won't lie, it's a homework assignment and I finally figured out how to get sed to behave in the way I expected but when running the program, I get: "Bad: modifier in $( )" if I specify a file that doesn't exist. How can I fix that? What I WANT to happen is that if the second argument is blank or the file doesn't exist, for it to go to the then portion of the if code.

Code:

#!/bin/tcsh                                                                       \
                                                                                   

set fileExt="$1"
set oldName="$2"

if (-r $oldName) then
    set newName = `echo $oldName | sed 's/.$/'$fileExt/''`
    mv $oldName $newName
else
    echo $oldName: No such file

endif

The tcsh version worked fine for me, though your regular expression doesn't replace the extension, it only replaces the last character. You need to escape the . if you want a literal . and look into grabbing everything after the last . in the file name.

The error you're getting is probably related to your use of the colon in the echo statement: https://www.google.com/search?q=tcsh...r+in+%24(+)%22.

EDIT: Bash has a much sexier way then your sed hack. Check out rule #6 here: http://bashcurescancer.com/10-steps-...l-scripts.html. Not sure if tcsh has an analog.

EDIT 2: You could leverage the word modifiers (the probably source of your error) to strip the old extension. Read the "History substitution" and "Variable substitution" sections of the tcsh man page. Lots of other good stuff in there too.

Looks like I figured it out:

Code:

#!/bin/bash                                                                       \
                                                                                  
fileExt="$1"

shift

for oldName in $*
    do
        if test -r $oldName;
            then
                newName=`echo $oldName | sed 's/[^\.]*$/'$fileExt'/'`
                mv $oldName $newName >& err.out
            else
                echo $oldName: No such file
        fi
done

Thanks for the help! This works as expected. I now need to go back through and check over the rest of it. We submit it through an "auto grader" tool that checks the script vigorously for many cases...

EDIT: Got it to work for all cases - Seems like that was insane. He said "test it" before submitting, I didn't think he'd cover so many cases!

Code:

#!/bin/bash                                                                       \
                                                                                  
fileExt="$1"

shift

oldName="$1"
#for oldName in $*                                                                 
while test "$oldName" != "";
    do
        if test -r "$oldName";
            then
                newName=`echo $oldName | sed "s/[^\.]*$/$fileExt/"`
                mv "$oldName" "$newName" >& err.out
            else
                echo $oldName: No such file
        fi
    shift
    oldName="$1"
done

What have I learned here? You have to use double quotes for your shell variables that contain spaces instead of single quotes - or so it seemed here -. Seems like that was the biggie here. Aside from bash's ..........ing about whitespace in variable assignment... Seems really picky and sloppy to me.