This option does not currently work with regular expressions. The syntax of regular expressions in agrep is in general the same as that for egrep . In particular, if word1 is the last word in a line and word2 is the first word in the next line, then the space will be substituted by a newline symbol and it will match. Thus, this is a way to overcome separation by a newline. The maximum size of the patternfile is limited to be 250Kb, and the maximum number of patterns is limited to be 30,000.
Standard input is the default if no input file is given.
There is no size limit for simple patterns. More complicated patterns are currently limited to approximately 30 characters. Lines are limited to 1024 characters. Records are limited to 48K, and may be truncated if they are larger than that.