Shell Programming and Scripting

A note to add: POSIX grep can use ERE and so can BSD sed (both through the -E switch) and so can ksh93 and bash. And Perl uses its own form of Regular Expression, neither Extended, nor Basic. GNU utilities use extensions to both BRE and ERE. In a UNIX context term regexp does not just refer to BRE but to ERE as well (but not to pattern matching).

I agree with Alister (and with yourself ) - even when formally right in theoretical informatics lingo - it is confusing to call the pattern matching used in parameter expansion a "regular expression", since the POSIX standards consistently uses the terms "regular expression" and "pattern matching" to distinguish between the two.

Shell Command Language

Interesting nonetheless


@Alister: interesting point about BRE not being formal regular language while ERE is. So then GNU ERE is not, since it supports back references...

ksh has the typeset -R option which can also do what you wish for

Code:

$ STR="Unix and Linux Forums"
$ typeset -R1 right=$STR
$ echo $right
r