grep

A favorite amongst shell programmers, it can be a convenient tool. It is both portable and fast, and a number of command-line options make it a powerful ally.
For portability, avoid using egrep and/or grep -E. This chart can help you find a portable syntax to replace extended syntax.
Element
Extended syntax
Portable syntax
Grouping
( and )
\( and \)
Quantity 1 or more
+ or {1,}
\+ or \{1,\}
Quantity 0 or 1
? or {0,1}
\? or \{0,1\}
Quantity N
{N}
\{N\}
Quantity N or less
{,N}
\{,N\}
OR
\∣
Word Bounding
\< and \> (same)
\< and \> (same)
From the GNU grep(1) manual, an example of an extended regular expression would be:
egrep '19|20|25' calendar
The portable syntax would be:
grep '19\|20\|25' calendar
You can search for more than one regular expression using the -e pattern option of grep. For example:
1 #!/bin/sh
2 printf 'a\nb\n' | grep -e a -e b
Produces:
a
b
This allows you to quickly search for one or more regular expressions. A match on any given regular expression will cause the line to be printed.
Last modified 2yr ago