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zero padding while renaming files

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# 1  
Old 03-19-2010
zero padding while renaming files
I wrote a script that renames all files in a folder with a generic numeric filename, but was wondering if there is a more elegant way to do the zero-padding.

BTW it is also pretty slow, I was thinking that was a result of the shell evaluating so many IF statements.

Anyone have any cool tricks to do this better/faster?

Code:
#!/usr/bin/bash

pre=1
cnt=1
list=$(ls)

for file in $list
    do
    if [ -f "$file" ] ; then
        ext=$(echo $file | awk '{n=split($0,e,"."); print (n > 1 ? e[n] : "")}')
        if [ "$cnt" -le 9 ] && [ "$cnt" -ge 1 ] ; then
            pad="0000000"
            fi
        if [ "$cnt" -le 99 ] && [ "$cnt" -ge 10 ] ; then
            pad="000000"
            fi
        if [ "$cnt" -le 999 ] && [ "$cnt" -ge 100 ] ; then
            pad="00000"
            fi
        if [ "$cnt" -le 9999 ] && [ "$cnt" -ge 1000 ] ; then
            pad="0000"
            fi
        if [ "$cnt" -le 99999 ] && [ "$cnt" -ge 10000 ] ; then
            pad="000"
            fi
        if [ "$cnt" -le 999999 ] && [ "$cnt" -ge 100000 ] ; then
            pad="00"
            fi
        if [ "$cnt" -le 9999999 ] && [ "$cnt" -ge 1000000 ] ; then
            pad="0"
            fi
        if [ "$cnt" -le 99999999 ] && [ "$cnt" -ge 10000000 ] ; then
            pad=""
            fi
        mv $file ${pre}${pad}${cnt}.${ext}
        cnt=$(( $cnt + 1 ))
    fi
    done
exit 0

# 2  
Old 03-19-2010
Quote:
Originally Posted by SporkFu
I wrote a script that renames all files in a folder with a generic numeric filename, but was wondering if there is a more elegant way to do the zero-padding.

BTW it is also pretty slow, I was thinking that was a result of the shell evaluating so many IF statements.

It's slow mostly because you are calling awk for every file.
Quote:
Anyone have any cool tricks to do this better/faster?

Code:
#!/usr/bin/bash

pre=1
cnt=1
list=$(ls)

for file in $list


That will break if any filename contains whitespace. Use wildcard expansion:
Code:
for file in *

Quote:
Code:
    do
    if [ -f "$file" ] ; then
        ext=$(echo $file | awk '{n=split($0,e,"."); print (n > 1 ? e[n] : "")}')


You don't need awk:
Code:
ext=${file##*.}

Quote:
Code:
        if [ "$cnt" -le 9 ] && [ "$cnt" -ge 1 ] ; then
            pad="0000000"
            fi
        mv $file ${pre}${pad}${cnt}.${ext}

Code:
printf -v pad "%07d" "$cnt"
mv "$file" "${pre}${pad}.${ext}"

# 3  
Old 03-19-2010
Dude, thanks for the tips, incorporated your suggestions and this works great:
Code:
#!/usr/bin/bash

pre=1
cnt=1

for file in *
    do
        if [ -f "$file" ] ; then
        ext=${file##*.}
        printf -v pad "%07d" "$cnt"
        mv "$file" "${pre}${pad}.${ext}"
        cnt=$(( $cnt + 1 ))
        fi
    done
exit 0

gonna have to figure out how

Quote:
${file##*.}
and

Quote:
printf -v pad "%07d" "$cnt"
actually works. That's some wizardry that is beyond me!
# 4  
Old 03-19-2010
Quote:
Originally Posted by SporkFu
gonna have to figure out how
Code:
${file##*.}

and
Code:
printf -v pad "%07d" "$cnt"

actually works.

Read the bash man page. The first is under Parameter Expansion, the other is a builtin command.
# 5  
Old 03-19-2010
Cool, I'll look it up there. Thanks again, this is the stuff they don't teach you in class.
# 6  
Old 03-19-2010
Quote:
Originally Posted by SporkFu
Cool, I'll look it up there. Thanks again, this is the stuff they don't teach you in class.

Note that the first item is part of the standard (i.e., POSIX) shell.

The second is only in bash.
# 7  
Old 03-20-2010
I get the printf part mostly, but this:
Code:
${parameter##word}

is godlike. I'll be back in a couple days after I have finished researching parameter expansion.

Virtual high fives to you, sir!
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