How can I change lower to upper using (three) parameters?

Question

Hello. I know there are similar topics here, but to be honest I didn't find solution for my problem. I've also checked stackoverflow but no result.

1. I have to make a bash script that will be changing files' names from lower to upper OR from upper to lower via parameters in command line. So when I put in command line:

   ./bashScript lower upper

   then all files in directory should change from lower to upper case.

2. I have to also add 3rd parameter that will let me change only one specific file. So for example I have to be able of putting in command line:

   ./bashScript lower upper fileName

I've created something like this:

#!/bin/bash

if test "$1" = "lower" && test "$2" = "upper"
then
for file in *; do
    if [ $0 != "$file" ] && [ $0 != "./$file" ]; then
    mv "$file" "$(echo $file | tr [:lower:] [:upper:])";
    fi
fi
done

elif test "$1" = "upper" && test "$2" = "lower"
then
for file in *; do
if [ $0 != "$file" ] && [ $0 != "./$file" ]; then
mv "$file" "$(echo $file | tr [:upper:] [:lower:])";
fi
done
fi

But this is not working at all. And I don't know how to make this 3rd parameter for one specific file. I'd be grateful if anyone could write a code or add to my code proper issues.

Thank you in advance.

Answer 1

Have a look at this:

#!/bin/bash

if [[ "$1" == "lower" && "$2" == "upper" ]] ; then
    EXPRESSION="y/a-z/A-Z/"
elif [[ "$1" == "upper" && "$2" == "lower" ]] ; then
    EXPRESSION="y/A-Z/a-z/"
else
    echo "Usage:     $0 lower upper [file]     OR     $0 upper lower [file]"
    exit 1
fi


if [[ -z "$3" ]] ; then
    shopt -s dotglob
    rename "$EXPRESSION" ./*
else
    rename "$EXPRESSION" "$3"
fi

You should normally use [[ ... ]] double brackets for conditional expressions in Bash. Inside them you can use e.g. == to compare for string equality (with both sides quoted), or && to combine two conditions with a logical AND.

Then, I decided to use the rename command instead of your construction with echo, tr and mv. It takes a "Perl expression" as first argument and any number of file names (like e.g. a shell glob result) after that and will rename all matching files accordingly.

The Perl expression that changes all lowercase letters in a name to uppercase letters is e.g. y/a-z/A-Z/. y is the command and means to translate all characters. a-z is a notation that matches all lowercase latin characters, A-Z for uppercase. Depending on the script arguments, we store either the expression for converting to upper- or to lowercase in the shell variable $EXPRESSION.

Then we check if a third script argument was given (-z is a Bash conditional check that is true if a string is empty). If not, we call the rename command with our stored expression and a ./* as shell glob to match all files in the current directory. The dotglob shell option we enabled before that makes sure this also matches hidden files with names that start with a dot, otherwise those would be omitted. However, if a third script argument was given, we pass that one on as argument.

Answer 2

I thought i would add my two pence worth, slightly different take on Byte Commander's answer.

#! /bin/bash

case $1 in
upper)  
    # check second argument to process a file if one given or the whole directory
    if [[ $2 > '' ]] #check if the second parameter is used (filename)
    then
        if [ -f $2 ] #check if the file exists
        then
            mv "$2" "$(echo $2 |tr [:lower:] [:upper:])" 
        else
            echo "$2 does not exist"
        fi          
    else    
        # process the whole directory
        for file in * 
        do
                if [ $0 != "$file" ] && [ $0 != "./$file" ]
            then
                    mv "$file" "$(echo $file | tr [:lower:] [:upper:])"
                fi
        done
    fi;;
lower)
    # check second argument to process a file if one given or the whole directory 
    if [[ $2 > '' ]] 
    then
        if [ -f $2 ] #check if the file exists
        then
            mv "$2" "$(echo $2 |tr [:upper:] [:lower:])" 
        else
            echo "$2 does not exist"
        fi          
    else    
        #process the whole directory
        for file in *; 
        do
                if [ $0 != "$file" ] && [ $0 != "./$file" ]
            then
                    mv "$file" "$(echo $file | tr [:upper:] [:lower:])"
                fi  
        done
    fi;;

--help)
    echo "Usage: $0 lower to lowercase entire directory "
    echo "Usage: $0 uppper to uppercase entire dirctory "
    echo "Usage: $0 lower [file] or upper [file] for a specific file"
    exit 1;;
esac