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unix: grepcidr

grepcidr 1.4 - Filter IP addresses matching IPv4 CIDR/network specification

Release date: 2013-11-20

Language: C
License: GNU GPL
Author: Jem Berkes

Download source: grepcidr-1.4.tar.gz [14K]
MD5 signature: grepcidr-1.4.tar.gz.md5


grepcidr can be used to filter a list of IP addresses against one or more Classless Inter-Domain Routing (CIDR) specifications, or arbitrary networks specified by an address range. As with grep, there are options to invert matching and load patterns from a file. grepcidr is capable of comparing thousands or even millions of IPs to networks with little memory usage and in reasonable computation time.

grepcidr has endless uses in network software, including: mail filtering and processing, network security, log analysis, and many custom applications.

Changes in version 1.4

Compiling and Installing


	make doc
	make install

To compile with performance optimizations, edit Makefile or use:

	make CFLAGS='-O2 -Wall -Werror'

Command usage

	grepcidr [-V] [-c] [-v] [-x] PATTERN [FILE]
	grepcidr [-V] [-c] [-v] [-x] [-e PATTERN | -f FILE] [FILE]

-V	Show software version
-c	Display count of the matching lines, instead of showing the lines
-v	Invert the sense of matching, to select non-matching IP addresses
-x	Strict non-regex search, look for single IP at start of line
-e	Specify pattern(s) on command-line
-f	Obtain CIDR and range pattern(s) from file

Important Change

Note that the default behaviour of grepcidr has changed in version 1.4 to find IP addresses anywhere on the line. This is the regex-patched behaviour that many users (including Debian distro) have been using. Use -x for the original (faster), non-regex behaviour of prior versions.

Usage Notes

PATTERN specified on the command line may contain multiple patterns separated by whitespace or commas. For long lists of network patterns, use -f to load a file where each line contains one pattern. Comment lines starting with # are ignored, as are any lines that don't parse.

Each pattern, whether on the command line or inside a file, may be:

a.b.c.d/xx	(CIDR format)
a.b.c.d-e.f.g.h	(IP range)
a.b.c.d		(Single IP)

By default as of version 1.4, grepcidr searches for IP addresses anywhere on the input line (using an internal regular expression search). This can sometimes lead to unexpected results. For example the following line will match the pattern (abts-kk-dynamic-

In this case, the reverse dotted IP in the hostname for this broadband user just happened to produce another valid ISP netblock, by coincidence.

Use the -x option to do a non-regex search, and grepcidr will only look for the single IP address at the start of the line (may be preceded by whitespace). This type of search is stricter, and faster. With -x the above example will match but not

Note that -v outputs IP addresses that don't match, as opposed to any line that doesn't match. When using -v, only lines containing an IP (which doesn't match the patterns) will be output.


grepcidr -f ournetworks blacklist > abuse.log
  Find customers (CIDR ranges in file) that appear in blacklist

grepcidr iplog
  Searches for any localnet IP addresses inside the iplog file

grepcidr "" iplog
  Searches for IPs matching indicated range in the iplog file

script | grepcidr -vf whitelist > blacklist
  Create a blacklist, with whitelisted networks removed (inverse)

grepcidr -f list1 list2
  Cross-reference two lists, outputs IPs common to both lists

Exit Status

As with grep: the exit status is 0 if matching IPs are found, and 1 if not found. If an error occurred the exit status is 2.


Thanks to Ryan Finnie for his work on the Debian package. I've adopted several of his changes including the Makefile, and the DocBook format which now is the source of the man page. Thanks to Ryan for writing the first manual in DocBook format.

Thanks to Jeff Makey who contributed a patch using regex to find IP addresses anywhere on the line.

Many thanks to Dick Wesseling who suggested an improved data structure format as well as binary search, to improve grepcidr performance.