Android shell script grep

Question

I'm attempting to write a script using the Android shell (with Busybox) to scan through some .xml files to extract information, however, I'm getting stuck on some optimization.

Shouldn't, for example,

(ax)b

match to

axbxc

It doesn't; when I try to execute this on Android (4.2.2, with Busybox 1.20.2, if it matters?).

echo axbxc > \sdcard\test.txt
grep "(ax)b" \sdcard\test.txt

returns nothing, while

grep "axb" \sdcard\test.txt

returns, as expected,

axbxc

Similarly, shouldn't

(?>ax)b

return axbxc as well? (This is the actual optimization I want to apply.)

What could be causing this problem? Additionally, does anyone know what regex engine Busybox uses, so that I can go and read up on it specifically?

mvp · Accepted Answer · 2013-05-24 05:13:52Z

4

To enable extended regular expressions in grep (and in busybox grep), you need to either use grep -E or use egrep (egrep is shortcut for grep -E).

I have tested this with busybox grep, and both methods work as expected and match your regex.

As for (?>ax)b - this would work only if you can use grep -P (support for Perl compatible regexes). However, busybox grep does not support this switch, so look-ahead and look-behind matches won't work.

edited May 24, 2013 at 5:13

answered May 24, 2013 at 5:08

mvp

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1 Comment

Firnagzen Over a year ago

... Oh. Thanks. Well, I feel silly now. Do you by any chance know what regex engine Busybox uses?

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