Why doesn't this simple RegEx work with sed?

Question

This is a really simple RegEx that isn't working, and I can't figure out why. According tothis, it should work.

I'm on a Mac (OS X 10.8.2).

script.sh

#!/bin/bashZIP="software-1.3-licensetypeone.zip"VERSION=$(sed 's/software-//g;s/-(licensetypeone|licensetypetwo).zip//g' <<< $ZIP)echo $VERSION

terminal

$ sh script.sh1.3-licensetypeone.zip

score 3 · Accepted Answer · 2012-11-14 03:35:18Z

Looking at the regex documentation for OS X 10.7.4 (but should apply to OP's 10.8.2), it is mentioned in the last paragraph that

Obsolete (basic) regular expressions differ in several respects. | is an ordinary character and there is no equivalent for its functionality...
... The parentheses for nested subexpressions are \(' and)'...

sed, without any options, uses basic regular expression (BRE).

To use | in OS X or BSD's sed, you need to enable extended regular expression (ERE) via-E option, i.e.

sed -E 's/software-//g;s/-(licensetypeone|licensetypetwo).zip//g'

p/s: \| in BRE is a GNU extension.

Alternative ways to extract version number

chop-chop (parameter expansion)

VERSION=${ZIP#software-}VERSION=${VERSION%-license*.zip}

sed
```
VERSION=$(sed 's/software-$.*$-license.*/\1/' <<< "$ZIP")
```
You don't necessarily have to match strings word-by-word with shell patterns or regex.

choroba 42.5k32760 · Answer 2 · 2012-11-12 12:59:24Z

up vote3 down vote

sed works with simple regular expressions. You have to backslash parentheses and a vertical bar to make it work.

sed 's/software-//g;s/-\(licensetypeone\|licensetypetwo\)\.zip//g'

Note that I backslashed the dot, too. Otherwise, it would have matched any character.

answered Nov 12 '12 at 12:59

choroba
42.5k32760

Copied and pasted your line in there, but it still didn't work for me.– curtisblackwellNov 12 '12 at 13:07

@curtisblackwell: Does yoursed support ; to separate commands? In some versions, multiple-e are needed: sed -e 's///' -e 's///'.– chorobaNov 12 '12 at 13:14

yeah, it supports multiple commands separated by;. I'm using that elsewhere.– curtisblackwellNov 12 '12 at 13:16

@curtisblackwell: Does $ZIP contain whitespace? If it can, use<<< "$ZIP".– chorobaNov 12 '12 at 13:18

no, it doesn't, but i should probably do use quotes in case it gets renamed.– curtisblackwellNov 12 '12 at 23:57

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glenn jackman 58.5k63166 · Answer 3 · 2012-11-12 18:09:45Z

up vote3 down vote

You can do this in the shell, don't need sed, parameter expansion suffices:

shopt -s extglobZIP="software-1.3-licensetypeone.zip"tmp=${ZIP#software-}VERSION=${tmp%-licensetype@(one|two).zip}

With a recent version of bash (may not ship with OSX) you can use regular expressions

if [[ $ZIP =~ software-([0-9.]+)-licensetype(one|two).zip ]]; then    VERSION=${BASH_REMATCH[1]}fi

or, if you just want the 2nd word in a hyphen-separated string

VERSION=$(IFS=-; set -- $ZIP; echo $2)

answered Nov 12 '12 at 18:09

glenn jackman
58.5k63166

Your last suggestion solves my problem. Thank you! However, I still don't understand why the RegEx doesn't work.– curtisblackwellNov 13 '12 at 0:00

choroba explained it in his answer. Different programs (perl, sed, bash, etc) implement regular expressions in different ways. With sed, you need to escape the parentheses to give them their special meaning.– glenn jackmanNov 13 '12 at 0:45

That sounds right, but even when I escaped them, it didn't work. Is it possible that my version of sed just doesn't support parentheses and/or pipes in regular expressions?– curtisblackwellNov 13 '12 at 1:00

highly unlikely. Did you also escape the pipe? Read choroba's answer very carefully. You will also want to checkman sed and (perhaps) man ed to learn about regexes implemented by sed.– glenn jackmanNov 13 '12 at 1:03

I read his answer carefully. Re-read many times, because I thought it was correct. However, even copying and pasting the RegEx didn't work. I'll check man sed again, and look into ed. Thanks.– curtisblackwellNov 13 '12 at 1:06

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csgwro 13114 · Answer 4 · 2012-11-12 13:03:08Z

$ man sed | grep "regexp-extended" -A2       -r, --regexp-extended              use extended regular expressions in the script.

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