How to extract a subsstring in a shell script

Question

Hi,
I need to extract a substring from a string in a shell script. Ideally using a regular expression, but a certain position (character n through n+4) would work in this case, too.
I am fairly familiar with regular expressions, I just don't know the syntax to use in a shell script
Thanks for any help!
Ingo

Answer 1

The equivalent of Bill's command in bash is:
expr $junk : '..\(...\)'Read the man page for expr, particularly the ':' operator. You can use any "basic" regular expressions, but not "extended" REs.
You can also use the stripping operators to remove stuff from the front or end of the string, optionally with a "greedy" match. So:
<pre>p=/usr/local/clamXav/man/man5/clamd.conf.5
echo ${p#????} # strip first 4 chars
/local/clamXav/man/man5/clamd.conf.5
echo ${p%????} # strip last 4 chars
/usr/local/clamXav/man/man5/clamd.co
echo ${p##*/} # greedy strip path components (basename)
clamd.conf.5
echo ${p%%man*} # Greedy strip from end
/usr/local/clamXav/</pre>I dare say these all work in zsh too.