gram_grep: grep for the 21st Century


gram_grep is a search tool that goes far beyond the capabilities of grep. Searches can span multiple lines and may be chained together in a variety of ways and can even utilise bison style grammars.

Maybe you want a search to ignore comments, or search only within strings. Maybe you have code that has SQL within strings and that SQL itself contains strings that you want to search in. The possibilities are endless and there is no limit to the sequence of sub-searches.

For example, here is how you would search for memory_file outside of C and C++ style comments:

gram_grep -vE "[/][/].*|[/][*](?s:.)*?[*][/]" -E memory_file main.cpp

A Note on DOS Prompt Escapes

Note that '^' is the escape character in the command prompt therefore if you want to use the '^' character you will have to double it up. The same goes for double quotes ('"') and in addition any regex using them will need surrounding with double quotes, as will any containing the pipe symbol ('|') (although in this case you do not to double it up).

Configuration Files Make Things Easier

It quickly gets tedious trying to correctly escape characters in a command shell, so we switch to a configuration file to also exclude strings:

gram_grep -f nosc.g main.cpp

The config file nosc.g looks like this:

'([^'\\]|\\.)*'                   skip()
["]([^"\\]|\\.)*["]               skip()
R["][(](?s:.)*?[)]["]             skip()
[/][/].*|[/][*](?s:.)*?[*][/]     skip()
memory_file                       1

Note how characters are also skipped just in case there is a character containing a double quote! Also note how we have moved our search for memory_file directly into the config file as this part of the config lists regexes that are passed to a lexer generator. This means that we specify the things we want to match (use 1 for the id in this case) or explicitly skip (use skip() in this case) all within the same section. This mode alone has already given us far more searching power than with traditional techniques.

If we wanted to only search in strings or comments, we would use 1 instead of skip() for those regexes and omit the memory_file line altogether. We would then pass memory_file with -E or -P as a command line parameter.

Source Control

Note that it is possible to issue a command to check out files from source control:

gram_grep -r -E "v4\.5\.1" -replace v4.5.2 -o -checkout "tf.exe checkout $1" *.csproj

The above example would replace v4.5.1 with v4.5.2 in *.csproj, checking out the files from TFS as they match. Note that there are also switches -startup and -shutdown where you can run other commands at startup and exit respectively if required (e.g., "tf.exe workspace /new /collection:http://... refactor /noprompt" and "tf.exe workspace /delete /collection:http://... refactor /noprompt").

The Configuration File Format

The config file has the following format:

<grammar/lexer directives>
<regex macros>

As implied above, the grammar/lexer directives, grammar and regex macros are all optional.

Here is an example of a simple grammar that recognises C++ strings split over multiple lines (strings.g):

NOTE: in order to successfully find strings it is necessary to filter out comments and chars.
As a subtlety, comments could contain apostrophes (or even unbalanced double quotes in
an extreme case)!
%token RawString String
list: String { match = substr($1, 1, 1); };
list: RawString { match = substr($1, 3, 2); };
list: list String { match += substr($2, 1, 1); };
list: list RawString { match += substr($2, 3, 2); };
["]([^"\\]|\\.)*["]                          String
R["][(](?s:.)*?[)]["]                        RawString
'([^'\\]|\\.)*'                              skip()
[ \t\r\n]+|[/][/].*|[/][*](?s:.)*?[*][/]     skip()

Although the grammar is just about as simple as it gets, note the scripting added. Each string fragment is joined into a match, that can then be searched on by a following search. This means we can search within C++ strings without worrying about how they are split over lines.

Note how we have switched from using 1 as the matching regex id to names which we have specified using %token and used in the grammar.

Example usage:

gram_grep -f sample_configs/strings.g -E memory_file main.cpp

The full list of scripting commands are listed below. You can see their use in the more sophisticated examples that follow later. $n, $from and $to refer to the item in the production you are interested in (numbering starts at 1).

Notes on Grammars

By default, the entire grammar will match. However, there are times you are only interested if specific parts of your grammar matches. If you want to only match on particular grammar rules, use {} just before the terminating semi-colon for that rule. This technique is shown in a later example.

Most of the time, the only grammar/lexer directive you will care about will be %token. However, the following are supported:

Command Line Switches for gram_grep


If an input file has a BOM (byte order marker), then that will be recognised. In the case of UTF-16, the contents will be automatically converted to UTF-8 in memory to allow uniform processing.

Unicode support can be enabled with the -utf8 switch. Two things happen with this switch enabled:


Searching for SQL INSERT Commands Without a Column List


%token INSERT INTO Name String VALUES
start: insert;
insert: INSERT into name VALUES;
into: INTO | %empty;
name: Name | Name '.' Name | Name '.' Name '.' Name;
(?i:INSERT)                                           INSERT
(?i:INTO)                                             INTO
(?i:VALUES)                                           VALUES
[.]                                                   '.'
(?i:[a-z_][a-z0-9@$#_]*|\[[a-z_][a-z0-9@$#_]*[ ]*\])  Name
'([^']|'')*'                                          String
\s+|--.*|[/][*](?s:.)*?[*][/]                         skip()

The command line looks like this:

gram_grep -r -f sample_configs/insert.g *.sql

Searching for SQL MERGE Commands Without WITH(HOLDLOCK) Within Strings Only

First the string extraction (strings.g):

%token RawString String
list: String { match = substr($1, 1, 1); };
list: RawString { match = substr($1, 3, 2); };
list: list String { match += substr($2, 1, 1); };
list: list RawString { match += substr($2, 3, 2); };
["]([^"\\]|\\.)*["]                          String
R["][(](?s:.)*?[)]["]                        RawString
'([^'\\]|\\.)*'                              skip()
[ \t\r\n]+|[/][/].*|[/][*](?s:.)*?[*][/]     skip()

Or if we wanted to scan C#:

%token String VString
list: String { match = substr($1, 1, 1); };
list: VString { match = substr($1, 2, 1); };
list: list '+' String { match += substr($3, 1, 1); };
list: list '+' VString { match += substr($3, 2, 1); };
ws [ \t\r\n]+
[+]                                    '+'
[\"]([^"\\]|\\.)*[\"]                  String
@[\"]([^\"]|[\"][\"])*["]              VString
'([^'\\]|\\.)*'                        skip()
{ws}|[/][/].*|[/][*](?s:.)*?[*][/]     skip()

Now the grammar to search inside the strings (merge.g):

merge: MERGE opt_top opt_into name opt_alias USING;
opt_top: %empty | TOP '(' Integer ')' opt_percent;
opt_percent: %empty | PERCENT;
opt_into: %empty | INTO;
name: Name | Name '.' Name | Name '.' Name '.' Name;
opt_alias: %empty | opt_as Name;
opt_as: %empty | AS;
(?i:AS)                                               AS
(?i:INTO)                                             INTO
(?i:MERGE)                                            MERGE
(?i:PERCENT)                                          PERCENT
(?i:TOP)                                              TOP
(?i:USING)                                            USING
\.                                                    '.'
\(                                                    '('
\)                                                    ')'
\d+                                                   Integer
(?i:[a-z_][a-z0-9@$#_]*|\[[a-z_][a-z0-9@$#_]*[ ]*\])  Name
\s+                                                   skip()

The command line looks like this:

gram_grep -r -f sample_configs/strings.g -f sample_configs/merge.g *.cpp

Looking for Uninitialised Variables in Headers

Note the use of {} here to specify that we only care when the rule item: Name; matches.

%token Bool Char Name NULLPTR Number String Type
start: decl;
decl: Type list ';';
list: item | list ',' item;
item: Name {};
item: Name '=' value;
value: Bool | Char | Number | NULLPTR | String;
NAME  [_A-Za-z][_0-9A-Za-z]*
=                                               '='
,                                               ','
;                                               ';'
true|TRUE|false|FALSE                           Bool
nullptr                                         NULLPTR
UWORD|WPARAM                                    Type
bool|(unsigned\s+)?char|double|float            Type
(unsigned\s+)?int((32|64)_t)?|long|size_t       Type
{NAME}(\s*::\s*{NAME})*(\s*[*])+                Type
{NAME}                                          Name
-?\d+([.]\d+)?                                  Number
'([^'\\]|\\.)*'                                 Char
["]([^\"\\]|\\.)*["]                            String
[ \t\r\n]+|[/][/].*|[/][*](?s:.)*?[*][/]        skip()

The command line looks like this:

gram_grep -r -f sample_configs/uninit.g *.h

Automatically Converting boost::format to std::format

Note the use of a variety of scripting commands:

%token Integer Name RawString String
start: '(' format list ')' '.' 'str' '(' ')'
    /* Erase the first "(" and the trailing ".str()" */
    { erase($1);
    erase($5, $8); };
start: 'str' '(' format list ')'
    /* Erase "str(" */
    { erase($1, $2); };
format: 'boost' '::' 'format' '(' string ')'
    /* Replace "boost" with "std" */
    /* Replace the format specifiers within the strings */
    { replace($1, 'std');
    replace_all($5, '%(\d+[Xdsx])', '{:$1}');
    replace_all($5, '%((?:\d+)?\.\d+f)', '{:$1}');
    replace_all($5, '%x', '{:x}');
    replace_all($5, '%[ds]', '{}');
    replace_all($5, '%%', '%');    
    erase($6); };
string: String;
string: RawString;
string: string String;
string: string RawString;
list: %empty;
list: list '%' param
    /* Replace "%" with ", " */
    { replace($2, ', '); };
param: Integer;
param: name
    /* Replace any trailing ".c_str()" calls with "" */
    { replace_all($1, '\.c_str\(\)$', ''); };
name: Name opt_func
    | name deref Name opt_func;
opt_func: %empty | '(' opt_param ')';
deref: '.' | '->' | '::';
opt_param: %empty | Integer | name;
\(                              '('
\)                              ')'
\.                              '.'
%                               '%'
::                              '::'
->                              '->'
boost                           'boost'
format                          'format'
str                             'str'
-?\d+                           Integer
\"([^"\\]|\\.)*\"               String
R\"\((?s:.)*?\)\"               RawString
'([^'\\]|\\.)*'                 skip()
[_a-zA-Z][_0-9a-zA-Z]*          Name
\s+|\/\/.*|\/\*(?s:.)*?\*\/     skip()

The command line looks like this:

gram_grep -o -r -f format.g *.cpp

Coping With Nested Constructs Without Caring What They Are

This example finds an if statement, its opening parenthesis and its closing parenthesis and copes with any parenthesis nested in between. We introduce the nonsense token anything so that we stop matching directly after the closing parenthesis and we rely on lexer states to cope with the nesting.

%token if anything
start: if '(' ')';
any (?s:.)
char '([^'\\]|\\.)+'
name [A-Z_a-z][0-9A-Z_a-z]*
string ["]([^"\\]|\\.)*["]|R["][(](?s:.)*?[)]["]
ws [ \t\r\n]+|[/][/].*|[/][*](?s:.)*?[*][/]
<INITIAL>if<PREBODY>      if
<PREBODY>[(]<BODY>        '('
<PREBODY>(?s:.)<.>        skip()
<BODY,PARENS>[(]<>PARENS> skip()
<PARENS>[)]<<>            skip()
<BODY>[)]<INITIAL>        ')'
<BODY,PARENS>{string}<.>  skip()
<BODY,PARENS>{char}<.>    skip()
<BODY,PARENS>{ws}<.>      skip()
<BODY,PARENS>{name}<.>    skip()
<BODY,PARENS>{any}<.>     skip()
{string}                  anything
{char}                    anything
{ws}                      anything
{name}                    anything
{any}                     anything

All of these example configs are available in the zip with a .g extension.


I used the following command line to build under Linux/g++:

g++ -o gram_grep main.cpp -std=c++17 -lstdc++fs

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