AGREP(l) AGREP(l)
Jan 17, 1992
NAME
agrep - search a file for a string or regular expression, with
approximate matching capabilities
SYNOPSIS
agrep [ -#cdehiklnpstvwxBDGIS ] pattern [ -f patternfile ] [
filename... ]
DESCRIPTION
agrep searches the input filenames (standard input is the default, but
see a warning under LIMITATIONS) for records containing strings which
either exactly or approximately match a pattern. A record is by
default a line, but it can be defined differently using the -d option
(see below). Normally, each record found is copied to the standard
output. Approximate matching allows finding records that contain the
pattern with several errors including substitutions, insertions, and
deletions. For example, Massechusets matches Massachusetts with two
errors (one substitution and one insertion). Running agrep -2
Massechusets foo outputs all lines in foo containing any string with
at most 2 errors from Massechusets. agrep supports many kinds of
queries including arbitrary wild cards, sets of patterns, and in
general, regular expressions. See PATTERNS below. It supports most
of the options supported by the grep family plus several more (but it
is not 100% compatible with grep). For more information on the
algorithms used by agrep see Wu and Manber, "Fast Text Searching With
Errors," Technical report #91-11, Department of Computer Science,
University of Arizona, June 1991 (available by anonymous ftp from
cs.arizona.edu in agrep/agrep.ps.1), and Wu and Manber, "Agrep -- A
Fast Approximate Pattern Searching Tool", To appear in USENIX
Conference 1992 January (available by anonymous ftp from
cs.arizona.edu in agrep/agrep.ps.2). As with the rest of the grep
family, the characters `$', `^', `*', `[', `]', `^', `|', `(', `)',
`!', and `\' can cause unexpected results when included in the
pattern, as these characters are also meaningful to the shell. To
avoid these problems, one should always enclose the entire pattern
argument in single quotes, i.e., 'pattern'. Do not use double quotes
("). When agrep is applied to more than one input file, the name of
the file is displayed preceding each line which matches the pattern.
The filename is not displayed when processing a single file, so if you
actually want the filename to appear, use /dev/null as a second file
in the list.
OPTIONS
-# # is a non-negative integer (at most 8) specifying the maximum
number of errors permitted in finding the approximate matches
(defaults to zero). Generally, each insertion, deletion, or
substitution counts as one error. It is possible to adjust the
relative cost of insertions, deletions and substitutions (see -I
-D and -S options).
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-c Display only the count of matching records.
-d 'delim'
Define delim to be the separator between two records. The
default value is '$', namely a record is by default a line.
delim can be a string of size at most 8 (with possible use of ^
and $), but not a regular expression. Text between two delim's,
before the first delim, and after the last delim is considered as
one record. For example, -d '$$' defines paragraphs as records
and -d '^From ' defines mail messages as records. agrep matches
each record separately. This option does not currently work with
regular expressions.
-e pattern
Same as a simple pattern argument, but useful when the pattern
begins with a `-'.
-f patternfile
patternfile contains a set of (simple) patterns. The output is
all lines that match at least one of the patterns in patternfile.
Currently, the -f option works only for exact match and for
simple patterns (any meta symbol is interpreted as a regular
character); it is compatible only with -c, -h, -i, -l, -s, -v,
-w, and -x options. see LIMITATIONS for size bounds.
-h Do not display filenames.
-i Case-insensitive search - e.g., "A" and "a" are considered
equivalent.
-k No symbol in the pattern is treated as a meta character. For
example, agrep -k 'a(b|c)*d' foo will find the occurrences of
a(b|c)*d in foo whereas agrep 'a(b|c)*d' foo will find substrings
in foo that match the regular expression 'a(b|c)*d'.
-l List only the files that contain a match. This option is useful
for looking for files containing a certain pattern. For example,
" agrep -l 'wonderful' * " will list the names of those files in
current directory that contain the word 'wonderful'.
-n Each line that is printed is prefixed by its record number in the
file.
-p Find records in the text that contain a supersequence of the
pattern. For example,
agrep -p DCS foo will match "Department of Computer Science."
-s Work silently, that is, display nothing except error messages.
This is useful for checking the error status.
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-t Output the record starting from the end of delim to (and
including) the next delim. This is useful for cases where delim
should come at the end of the record.
-v Inverse mode - display only those records that do not contain the
pattern.
-w Search for the pattern as a word - i.e., surrounded by non-
alphanumeric characters. The non-alphanumeric must surround the
match; they cannot be counted as errors. For example, agrep -w
-1 car will match cars, but not characters.
-x The pattern must match the whole line.
-y Used with -B option. When -y is on, agrep will always output the
best matches without giving a prompt.
-B Best match mode. When -B is specified and no exact matches are
found, agrep will continue to search until the closest matches
(i.e., the ones with minimum number of errors) are found, at
which point the following message will be shown: "the best match
contains x errors, there are y matches, output them? (y/n)" The
best match mode is not supported for standard input, e.g.,
pipeline input. When the -#, -c, or -l options are specified,
the -B option is ignored. In general, -B may be slower than -#,
but not by very much.
-Dk Set the cost of a deletion to k (k is a positive integer). This
option does not currently work with regular expressions.
-G Output the files that contain a match.
-Ik Set the cost of an insertion to k (k is a positive integer).
This option does not currently work with regular expressions.
-Sk Set the cost of a substitution to k (k is a positive integer).
This option does not currently work with regular expressions.
PATTERNS
agrep supports a large variety of patterns, including simple strings,
strings with classes of characters, sets of strings, wild cards, and
regular expressions.
Strings
any sequence of characters, including the special symbols `^' for
beginning of line and `$' for end of line. The special
characters listed above ( `$', `^', `*', `[', `^', `|', `(', `)',
`!', and `\' ) should be preceded by `\' if they are to be
matched as regular characters. For example, \^abc\\ corresponds
to the string ^abc\, whereas ^abc corresponds to the string abc
at the beginning of a line.
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Classes of characters
a list of characters inside [] (in order) corresponds to any
character from the list. For example, [a-ho-z] is any character
between a and h or between o and z. The symbol `^' inside []
complements the list. For example, [^i-n] denote any character
in the character set except character 'i' to 'n'. The symbol `^'
thus has two meanings, but this is consistent with egrep. The
symbol `.' (don't care) stands for any symbol (except for the
newline symbol).
Boolean operations
agrep supports an `and' operation `;' and an `or' operation `,',
but not a combination of both. For example, 'fast;network'
searches for all records containing both words.
Wild cards
The symbol '#' is used to denote a wild card. # matches zero or
any number of arbitrary characters. For example, ex#e matches
example. The symbol # is equivalent to .* in egrep. In fact, .*
will work too, because it is a valid regular expression (see
below), but unless this is part of an actual regular expression,
# will work faster.
Combination of exact and approximate matching
any pattern inside angle brackets <> must match the text exactly
even if the match is with errors. For example, <mathemat>ics
matches mathematical with one error (replacing the last s with an
a), but mathe<matics> does not match mathematical no matter how
many errors we allow.
Regular expressions
The syntax of regular expressions in agrep is in general the same
as that for egrep. The union operation `|', Kleene closure `*',
and parentheses () are all supported. Currently '+' is not
supported. Regular expressions are currently limited to
approximately 30 characters (generally excluding meta
characters). Some options (-d, -w, -f, -t, -x, -D, -I, -S) do
not currently work with regular expressions. The maximal number
of errors for regular expressions that use '*' or '|' is 4.
EXAMPLES
agrep -2 -c ABCDEFG foo
gives the number of lines in file foo that contain ABCDEFG within
two errors.
agrep -1 -D2 -S2 'ABCD#YZ' foo
outputs the lines containing ABCD followed, within arbitrary
distance, by YZ, with up to one additional insertion (-D2 and -S2
make deletions and substitutions too "expensive").
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agrep -5 -p abcdefghij /usr/dict/words
outputs the list of all words containing at least 5 of the first
10 letters of the alphabet in order. (Try it: any list starting
with academia and ending with sacrilegious must mean something!)
agrep -1 'abc[0-9](de|fg)*[x-z]' foo
outputs the lines containing, within up to one error, the string
that starts with abc followed by one digit, followed by zero or
more repetitions of either de or fg, followed by either x, y, or
z.
agrep -d '^From ' 'breakdown;internet' mbox
outputs all mail messages (the pattern '^From ' separates mail
messages in a mail file) that contain keywords 'breakdown' and
'internet'.
agrep -d '$$' -1 '<word1> <word2>' foo
finds all paragraphs that contain word1 followed by word2 with
one error in place of the blank. 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. Note that -d '$$' (or another delim which spans more
than one line) is necessary, because otherwise agrep searches
only one line at a time.
agrep '^agrep' <this manual>
outputs all the examples of the use of agrep in this man pages.
SEE ALSO
ed(1), ex(1), grep(1V), sh(1), csh(1).
BUGS/LIMITATIONS
Any bug reports or comments will be appreciated! Please mail them to
sw@cs.arizona.edu or udi@cs.arizona.edu Regular expressions do not
support the '+' operator (match 1 or more instances of the preceding
token). These can be searched for by using this syntax in the
pattern:
'pattern(pattern)*'
(search for strings containing one instance of the pattern, followed
by 0 or more instances of the pattern). The following can cause an
infinite loop: agrep pattern * > output_file. If the number of
matches is high, they may be deposited in output_file before it is
completely read leading to more matches of the pattern within
output_file (the matches are against the whole directory). It's not
clear whether this is a "bug" (grep will do the same), but be warned.
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. However, if standard input is
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keyed in directly (as opposed to through a pipe, for example) agrep
may not work for some non-simple patterns. 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. The limit of record length can be changed by modifying the
parameter Max_record in agrep.h.
DIAGNOSTICS
Exit status is 0 if any matches are found, 1 if none, 2 for syntax
errors or inaccessible files.
AUTHORS
Sun Wu and Udi Manber, Department of Computer Science, University of
Arizona, Tucson, AZ 85721. {sw|udi}@cs.arizona.edu.
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