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need help understanding mv


 
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Top Forums Shell Programming and Scripting need help understanding mv
# 1  
Old 09-24-2009
need help understanding mv

I just started shell coding and I'm a bit confused on how 'mv' works can someone explain to me how it works and if i did this correctly. Thanks.

Code:
echo "Enter Name of the first file:"
    read file1
    #echo $file1
    if [! -e $file1]; then
        echo "Sorry, file does not exist."
        exit 1
    fi

    echo "Name of the second file:"
    read file2

    if [! -e $file2]; then    
        echo "Sorry, file does not exist."
        exit 1
    else
        #echo $file1
        #echo $file2
        set tmp = $file1
        mv "$file2" "$file1"
        mv "$tmp" "$file2"
    fi;;

once it gets down to the 'mv' i get
Quote:
mv: cannot stat `file.txt': No such file or directory
which confuses me since both files pass the if statements. Can someone clarify?
# 2  
Old 09-24-2009
try.. these with spaces.
Code:
if [ ! -e $file1 ]; then

although i would prefer it this way

Code:
if [ ! -f $file1 ]; then

# 3  
Old 09-28-2009
sorry for the long wait. Thanks. After fixing the spaces I have
Code:
echo "Enter Name of the first file:"
    read file1
    #echo $file1
    if [ ! -f $file1]; then
        echo "Sorry, file does not exist."
        exit 1
    fi

    echo "Name of the second file:"
    read file2

    if [ ! -f $file2]; then    
        echo "Sorry, file does not exist."
        exit 1
    else
        #echo $file1
        #echo $file2
        set tmp = $file1
        mv "$file2" "$file1"
        mv "$tmp" "$file2"
    fi;;



But when I run it I still get this error

Quote:
Enter Name of the first file:
txt.txt
./Assgn1.bash: line 52: [: missing `]'
Name of the second file:
file.txt
./Assgn1.bash: line 60: [: missing `]'
mv: cannot stat `file.txt': No such file or directory
mv: cannot stat `': No such file or director
Am using the mv in the wrong manner?
(I'm trying to swap the name of the files.)
# 4  
Old 09-28-2009
you still have not followed the suggested change completely..
# 5  
Old 09-28-2009
I dislike white spaces . . . thanks. Can anyone explain

Quote:
mv: missing destination file operand after `file'
Try `mv --help' for more information.
Code:
set tmp = $file1
		mv  $file2 $file1
		mv  $tmp $file2

After the first "mv" is executed $file2 gets deleted so when the second "mv" command occurs there is no longer a $file2. Is there a way to not delete $file2 when it gets copied to $file1?
# 6  
Old 09-28-2009
You should by now have a space after "[" and a space before "]".

The logic in this bit needs attention if you want to swap the filenames:

Quote:
set tmp = $file1
mv "$file2" "$file1"
mv "$tmp" "$file2"
Code:
Maybe try:
        # Rename both files to preserve their permissions.
        mv "${file1}" "${file1}.TMP"
        mv "${file2}" "${file2}.TMP"
        # Cross-rename the files to their final names
        mv "${file1}.TMP" "${file2}"
        mv "${file2}.TMP" "${file1}"


BTW. I can't make "set tmp = $file1" do anything useful.

Some may argue that the filename swap can be done in three steps (not four). However this can introduce unexpected changes to file permissions.

Footnote: Notice the curly braces. You will rarely find cause to not use them!

Footnote 2: Providing both files are on the same filesystem a "mv" command just changes the name of the inode. It is very quick and the contents of the files do not move. If the files are on different filesystems they do actually move!

Last edited by methyl; 09-28-2009 at 12:47 PM.. Reason: Footnote
# 7  
Old 09-28-2009
Thanks guys. Can you briefly explain the curly brackets.

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