s6-portable-utils
Software
skarnet.org
 The s6-grep program 
 s6-grep matches its input against a pattern.
 Interface 
     s6-grep [ -E | -F ] [ -i ] [ -c ] [ -n ] [ -q ] [ -v ] pattern
 -  s6-grep compiles pattern as a
Basic
Regular Expression 
-  It reads stdin and matches every line against this regexp 
-  If the line matches, it prints it to stdout 
-  It exits on EOF with code 0 if one or more lines matched and 1
otherwise. 
 Options 
 -  -F : pattern is not compiled as a BRE, but is
interpreted as a literal string. 
-  -E : pattern is not compiled as a BRE, but as an
Extended
Regular Expression (ERE). 
-  -i : ignore case during the match 
-  -c : do not write normal output; only write the number of
lines that have matched pattern after EOF is received 
-  -n : precede every output line by its number and a colon.
The first input line has number 1. 
-  -q : do not write anything to stdout 
-  -v : invert the pattern matching (select lines that do not
match pattern). 
 Posixness 
 s6-grep is not suitable as a Single Unix
grep
program.