Egrep replacement for Or operator

UNIX for Beginners Q & A
1

I'm wondering if there is a replacement for using the | operator for an egrep expression for example say I wanted to match this pattern "out" or "outside" how can that be done without doing egrep "(out|side)" file

2

You can use

grep -e 'foo' -e 'bar' file

---
out and outside may be tricky because out will also find matches for outside , so you would need to use something extra in the search to make a distinction..

3 
grep -F -e 'out' -e 'outside'  somefile

Fixed strings (-F) eliminates problems with characters like * or [ that can be taken as part of a regular expression. -F turns off regex interpretations and searches so you find exactly what you type inside the single quotes.

PS - the pipe character performs alternation (sort of like an or) and only works in regex mode. So

grep '\b(out|outside)\b' somefile

would be how to correctly use alternation for those two whole words.

1 Like
4

Note that GNU grep uses the glibc RE engine that has got some perl extensions (PRE). \b is such an addition.
GNU grep needs an (also nonstandard) \| for OR while | is standard for ERE (egrep or grep -E).
So you can write either

grep -E '\b(out|outside)\b' somefile

or

grep '\b\(out\|outside\)\b' somefile

Both need GNU grep and glibc.
A bit more spread (but also no standard) are \< and \> (left and right word boundary) for grep (not egrep).
Standard (portable) are

grep -w -e "out" -e "outside"

grep -w "out
outside"

(multi-line)