Regular Expressions in BASH?

Question

I am ok with regular expressions in Perl but not had to do it in BASH before.

I tried to google for some sort of tutorial on it but didn't see any really good ones yet the way there are with Perl.

What I am trying to achieve is to strip /home/devtestdocs/devtestdocs-repo/ out of a variable called $filename and replace it with another variable called $testdocsdirurl

Hopefully that makes sense and if anybody has any good links that would be much appreciated.

Another way might be is if there is already a function someone has written to do a find and replace in bash.

I don't see the need for regular expressions here. Can you explain why you think you need them? — user3850
– user3850, Commented Jul 27, 2011 at 14:19

João Silva · Accepted Answer · 2011-07-27 14:34:20Z

3

sed is the typical weapon of choice for string manipulation in Unix:

echo $filename | sed s/\\/home\\/devtestdocs\\/devtestdocs-repo\\//$testdocsdirurl/

Also, as hop suggests, you can use the @ syntax to avoid escaping the path:

echo $filename | sed s@/home/devtestdocs/devtestdocs-repo/@$testdocsdirurl@

edited Jul 27, 2011 at 14:34

answered Jul 27, 2011 at 14:07

João Silva

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2 Comments

user3850 Over a year ago

sed typically also understands s@pattern@string@ so you don't have to painfully escape slashes in a path.

nhed Over a year ago

@JG,@hop just to set the record straight - sed will actually take any character you like... so that even a silly expression like this will work echo SSSSS | sed 'sqSqsqg'

DarkDust · Accepted Answer · 2011-07-27 14:15:21Z

3

You can achieve this without a regular expression:

somepath="/foo/bar/baz"
newprefix="/alpha/beta/"
newpath="$newprefix${somepath##/foo/bar/}"

answered Jul 27, 2011 at 14:15

DarkDust

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Comments

mykhal · Accepted Answer · 2011-07-27 14:18:42Z

3

yes, bash supports regular expressions, e.g.

$ [[ 'abc' =~ (.)(.)(.) ]]
$ echo ${BASH_REMATCH[1]}
a
$ echo ${BASH_REMATCH[2]}
b

but you might rather want to use basename utility

$ f='/some/path/file.ext'
$ echo "/new/path/$(basename $f)"
/new/path/file.ext

excellent source of info is bash manual page

answered Jul 27, 2011 at 14:18

mykhal

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Comments

glenn jackman · Accepted Answer · 2011-07-27 14:27:16Z

1

With bash

pattern=/home/devtestdocs/devtestdocs-repo/
testdocsdirurl=/tmp/
filename=/foo/bar/home/devtestdocs/devtestdocs-repo/filename
echo ${filename/$pattern/$testdocsdirurl}  # => /foo/bar/tmp/filename

answered Jul 27, 2011 at 14:27

glenn jackman

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Comments

user3850 · Accepted Answer · 2011-07-27 14:16:44Z

0

Why do you need regular expressions for this?

These are just a few possibilities:

$ filename=/home/devtestdocs/devtestdocs-repo/foo.txt
$ echo ${filename/'/home/devtestdocs/devtestdocs-repo/'/'blah/'}
blah/foo.txt
$ basename $filename
foo.txt
$ realfilename=$(basename "$filename")

answered Jul 27, 2011 at 14:16

user3850

3 Comments

Marcus Borkenhagen Over a year ago

see also: gnu.org/software/bash/manual/…

martincarlin87 Over a year ago

thanks, I just thought that using a regular expression would be the way to go on this one.

user3850 Over a year ago

@martincarlin87: a good rule of thumb is: regex should be the last way you should go about solving any problem.

The Mask · Accepted Answer · 2011-07-27 14:34:31Z

0

you're looking for an example of how use regular expressions in powershell?

is there an example here:

$input = "hello,123"
$pattern = ([regex]"[0-9]+")
$match = $pattern.match($input)
$ok = $input -match $pattern #return an boolean value if matched..
if($ok) { 
    $output = $match.groups[0].value
    [console]::write($output)
 } else {
   //no match
 }

in 'bash classic' regular expressions usage is precarious. you can use this: http://www.robvanderwoude.com/findstr.php

answered Jul 27, 2011 at 14:34

The Mask

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1 Comment

DarkDust Over a year ago

He asked for the UNIX shell bash (Bourne Again SHell), not for batch files or the Window PowerShell.

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