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I have many files of the form


I want to insert a period between the sw's and the number values. How can I accomplish this?

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up vote 4 down vote accepted

On Linux:

rename 'sw' 'sw.' sw*

On Debian, Ubuntu and derivatives, use rename.ul instead of rename (rename is a different file renaming command on those distributions).

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Whups. Wrong link. :( – Daniel Pittman Mar 2 '12 at 18:14
@Daniel: What do you mean "wrong link"? – rsaw Mar 2 '12 at 18:17
I edited my comment - apparently there is a second utility by the name rename out there. Which is awesome. I linked to the wrong manual page, but didn't notice because they are close enough... – Daniel Pittman Mar 2 '12 at 18:19
Gotcha. It's interesting that you say the perl rename is usually the default -- I've never run into it before at all. As you say, the rename I'm familiar with should be on most linux boxen, shipping with util-linux. – rsaw Mar 2 '12 at 18:47
I am as surprised as you are, in the opposite direction. :) – Daniel Pittman Mar 2 '12 at 19:05

If you don't have rename and don't feel like downloading it, use this:

for file in sw*; do
    mv "$file" "${file/sw/sw.}"
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Be aware that the pattern substitution ${file/sw/sw.}" also matches files like FOOsw001. Besides - this kind of substitution is not supported by all shells. Removing a prefix pattern should be more appropriate and portable: "$sw.{file#sw}" – maxschlepzig Mar 2 '12 at 19:16
@maxschlepzig I suppose it would, but because of the glob all names it encounters necessarily begin with sw. Good to point out in general though. – Kevin Mar 2 '12 at 19:20

If you can can express the transformation as a Perl regular expression, rename that ships with Perl is a great choice. It applies a Perl expression to each filename, then changes the name if it is different. Often, a Perl regular expression substitution is what you want:

rename 's/sw/sw./' sw*

This is different from the rename(1) that ships with util-linux-ng, but normally the Perl version is the default. See man 1 rename to check which one your system has.

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Can you help me to understand what the / notation means? – Paul Mar 2 '12 at 18:09
Hopefully that edit is clearer: the man page was for a different utility with the same name, and I didn't notice because it was close enough. The Perl rename applies a Perl expression; 's///' is a regular expression substitution. – Daniel Pittman Mar 2 '12 at 18:18
If this rename expression is indeed a regular expression, the . character would mean "any one character", so it should be escaped in order to be taken literally. – user13742 Mar 2 '12 at 18:45
@hesse, it would in the match part, not in the replacement part. :) – Daniel Pittman Mar 2 '12 at 19:05
The Perl version is the default in Debian and derivatives including Ubuntu. It's not shipped by other distributions. – Gilles Mar 2 '12 at 23:01

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