remove everything but the date

[mc]

Hi all,

I have several files in a folder. Each filename contains a date
occurrence in the format yyyyMMdd (eg. 20130401)

Using bash, how can I rename the files removing everything but the date?

For example:
"02file_20130401foo.txt" ---> "20130401.txt"

I don't need to verify the date, I know it is always valid and there is
just one occurrence of the pattern yyyyMMdd.

Thanks for your help,

mc.

[Janis Papanagnou]

To be on the safe side using POSIX only code you can do

pat=[0-9][0-9][0-9][0-9][0-9][0-9][0-9][0-9]
for f in *${pat}*
do
pref=${f%${pat}*}
suff=${f#*${pat}}
ff=${f#${pref}}
ff=${ff%${suff}}
ext=${f##*.}
mv -i "$f" "${ff}.${ext}"
done

With a ksh93 and back-references you can do

for f in *${pat}*
do
mv -i "$f" "${f/*@(${pat})*.@(*)/\1.\2}"
done

Not sure whether the latter is supported by bash (with extglob set).

Janis

[Thomas 'PointedEars' Lahn]

As you can see, this is non-trivial in a sh or ksh-compatible shell.
Why not use the right tool for the right job?

find . -name . -or -prune rename 's/^.*(\d{8}).*(\..+)?$/\1\2/' {} +

If you are sure about the date, you could specify further, to avoid false
positives:

find . -name . -or -prune rename 's/^.*(20\d{6}).*(\..+)?$/\1\2/' {} +

--
PointedEars

Twitter: @PointedEars2
Please do not Cc: me. / Bitte keine Kopien per E-Mail.

[Chris F.A. Johnson]

On 2013-04-11, Thomas 'PointedEars' Lahn wrote:
> mc wrote:
>
>> I have several files in a folder. Each filename contains a date
>> occurrence in the format yyyyMMdd (eg. 20130401)
>>
>> Using bash, how can I rename the files removing everything but the date?
>>
>> For example:
>> "02file_20130401foo.txt" ---> "20130401.txt"
>>
>> I don't need to verify the date, I know it is always valid and there is
>> just one occurrence of the pattern yyyyMMdd.
>
> As you can see, this is non-trivial in a sh or ksh-compatible shell.
> Why not use the right tool for the right job?
>
> find . -name . -or -prune rename 's/^.*(\d{8}).*(\..+)?$/\1\2/' {} +
>
> If you are sure about the date, you could specify further, to avoid false
> positives:
>
> find . -name . -or -prune rename 's/^.*(20\d{6}).*(\..+)?$/\1\2/' {} +

rename is not an operator in either POSIX or GNU find (unless it's a
very recent addition), nor is it a standard command (and there are
at least two versions in the wild with differing syntax).

--
Chris F.A. Johnson, author <http://shell.cfajohnson.com/>
===================================================================
Shell Scripting Recipes: A Problem-Solution Approach (2005, Apress)
Pro Bash Programming: Scripting the GNU/Linux Shell (2009, Apress)

[Thomas 'PointedEars' Lahn]

Chris F.A. Johnson wrote:

> On 2013-04-11, Thomas 'PointedEars' Lahn wrote:
>> mc wrote:
>>> I have several files in a folder. Each filename contains a date
>>> occurrence in the format yyyyMMdd (eg. 20130401)
>>>
>>> Using bash, how can I rename the files removing everything but the date?
>>>
>>> For example:
>>> "02file_20130401foo.txt" ---> "20130401.txt"
>>>
>>> I don't need to verify the date, I know it is always valid and there is
>>> just one occurrence of the pattern yyyyMMdd.
>>
>> As you can see, this is non-trivial in a sh or ksh-compatible shell.
>> Why not use the right tool for the right job?
>>
>> find . -name . -or -prune rename 's/^.*(\d{8}).*(\..+)?$/\1\2/' {} +
>>
>> If you are sure about the date, you could specify further, to avoid false
>> positives:
>>
>> find . -name . -or -prune rename 's/^.*(20\d{6}).*(\..+)?$/\1\2/' {} +
>
> rename is not an operator in either POSIX or GNU find (unless it's a
> very recent addition), nor is it a standard command (and there are
> at least two versions in the wild with differing syntax).

Should have (obviously) been

find . -name . -or -prune -exec rename 's/^.*(20\d{6}).*(\..+)?$/\1\2/' {} +

rename(1) comes with the Perl distribution (as a symlink to prename). That
does not preclude the possibility of using it; it might even be an argument
for using it. Which two versions are you talking about?

The approach can be adjusted to use sed(1) or awk(1) instead, POSIX-
compliant or not.

[Chris F.A. Johnson]

The Perl version and this one:

$ file /usr/bin/rename
/usr/bin/rename: ELF 32-bit LSB executable, Intel 80386, version 1 (SYSV), dynamically linked (uses shared libs), for GNU/Linux 2.6.9, stripped

[Thomas 'PointedEars' Lahn]

Chris F.A. Johnson wrote:

> On 2013-04-12, Thomas 'PointedEars' Lahn wrote:

>> […]

>> rename(1) comes with the Perl distribution (as a symlink to prename).
>> That does not preclude the possibility of using it; it might even be an
>> argument for using it. Which two versions are you talking about?
>
> The Perl version and this one:
>
> $ file /usr/bin/rename
> /usr/bin/rename: ELF 32-bit LSB executable, Intel 80386, version 1 (SYSV),
> dynamically linked (uses shared libs), for GNU/Linux 2.6.9, stripped

What would be the best way to tell them apart?