What are the undocumented features and limitations of the Windows FINDSTR command?
The Windows FINDSTR command is horribly documented. There is very basic command line help available through FINDSTR /?, or HELP FINDSTR, but it is
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Answer continued from part 1 above - I've run into the 30,000 character answer limit :-(
Limited Regular Expressions (regex) Support
FINDSTR support for regular expressions is extremely limited. If it is not in the HELP documentation, it is not supported.Beyond that, the regex expressions that are supported are implemented in a completely non-standard manner, such that results can be different then would be expected coming from something like grep or perl.
Regex Line Position anchors ^ and $
^matches beginning of input stream as well as any position immediately following a <LF>. Since FINDSTR also breaks lines after <LF>, a simple regex of "^" will always match all lines within a file, even a binary file.$matches any position immediately preceding a <CR>. This means that a regex search string containing$will never match any lines within a Unix style text file, nor will it match the last line of a Windows text file if it is missing the EOL marker of <CR><LF>.Note - As previously discussed, piped and redirected input to FINDSTR may have
<CR><LF>appended that is not in the source. Obviously this can impact a regex search that uses$.Any search string with characters before
^or after$will always fail to find a match.Positional Options /B /E /X
The positional options work the same as^and$, except they also work for literal search strings./B functions the same as
^at the start of a regex search string./E functions the same as
$at the end of a regex search string./X functions the same as having both
^at the beginning and$at the end of a regex search string.Regex word boundary
\<must be the very first term in the regex. The regex will not match anything if any other characters precede it.\<corresponds to either the very beginning of the input, the beginning of a line (the position immediately following a <LF>), or the position immediately following any "non-word" character. The next character need not be a "word" character.\>must be the very last term in the regex. The regex will not match anything if any other characters follow it.\>corresponds to either the end of input, the position immediately prior to a <CR>, or the position immediately preceding any "non-word" character. The preceding character need not be a "word" character.Here is a complete list of "non-word" characters, represented as the decimal byte code. Note - this list was compiled on a U.S machine. I do not know what impact other languages may have on this list.
001 028 063 179 204 230 002 029 064 180 205 231 003 030 091 181 206 232 004 031 092 182 207 233 005 032 093 183 208 234 006 033 094 184 209 235 007 034 096 185 210 236 008 035 123 186 211 237 009 036 124 187 212 238 011 037 125 188 213 239 012 038 126 189 214 240 014 039 127 190 215 241 015 040 155 191 216 242 016 041 156 192 217 243 017 042 157 193 218 244 018 043 158 194 219 245 019 044 168 195 220 246 020 045 169 196 221 247 021 046 170 197 222 248 022 047 173 198 223 249 023 058 174 199 224 250 024 059 175 200 226 251 025 060 176 201 227 254 026 061 177 202 228 255 027 062 178 203 229Regex character class ranges [x-y]
Character class ranges do not work as expected. See this question: Why does findstr not handle case properly (in some circumstances)?, along with this answer: https://stackoverflow.com/a/8767815/1012053.The problem is FINDSTR does not collate the characters by their byte code value (commonly thought of as the ASCII code, but ASCII is only defined from 0x00 - 0x7F). Most regex implementations would treat [A-Z] as all upper case English capital letters. But FINDSTR uses a collation sequence that roughly corresponds to how SORT works. So [A-Z] includes the complete English alphabet, both upper and lower case (except for "a"), as well as non-English alpha characters with diacriticals.
Below is a complete list of all characters supported by FINDSTR, sorted in the collation sequence used by FINDSTR to establish regex character class ranges. The characters are represented as their decimal byte code value. I believe the collation sequence makes the most sense if the characters are viewed using code page 437. Note - this list was compiled on a U.S machine. I do not know what impact other languages may have on this list.
001 002 003 004 005 006 007 008 014 015 016 017 018 019 020 021 022 023 024 025 026 027 028 029 030 031 127 039 045 032 255 009 010 011 012 013 033 034 035 036 037 038 040 041 042 044 046 047 058 059 063 064 091 092 093 094 095 096 123 124 125 126 173 168 155 156 157 158 043 249 060 061 062 241 174 175 246 251 239 247 240 243 242 169 244 245 254 196 205 179 186 218 213 214 201 191 184 183 187 192 212 211 200 217 190 189 188 195 198 199 204 180 181 182 185 194 209 210 203 193 207 208 202 197 216 215 206 223 220 221 222 219 176 177 178 170 248 230 250 048 172 171 049 050 253 051 052 053 054 055 056 057 236 097 065 166 160 133 131 132 142 134 143 145 146 098 066 099 067 135 128 100 068 101 069 130 144 138 136 137 102 070 159 103 071 104 072 105 073 161 141 140 139 106 074 107 075 108 076 109 077 110 252 078 164 165 111 079 167 162 149 147 148 153 112 080 113 081 114 082 115 083 225 116 084 117 085 163 151 150 129 154 118 086 119 087 120 088 121 089 152 122 090 224 226 235 238 233 227 229 228 231 237 232 234Regex character class term limit and BUG
Not only is FINDSTR limited to a maximum of 15 character class terms within a regex, it fails to properly handle an attempt to exceed the limit. Using 16 or more character class terms results in an interactive Windows pop up stating "Find String (QGREP) Utility has encountered a problem and needs to close. We are sorry for the inconvenience." The message text varies slightly depending on the Windows version. Here is one example of a FINDSTR that will fail:echo 01234567890123456|findstr [0-9][0-9][0-9][0-9][0-9][0-9][0-9][0-9][0-9][0-9][0-9][0-9][0-9][0-9][0-9][0-9]This bug was reported by DosTips user Judago here. It has been confirmed on XP, Vista, and Windows 7.
Regex searches fail (and may hang indefinitely) if they include byte code 0xFF (decimal 255)
Any regex search that includes byte code 0xFF (decimal 255) will fail. It fails if byte code 0xFF is included directly, or if it is implicitly included within a character class range. Remember that FINDSTR character class ranges do not collate characters based on the byte code value. Character<0xFF>appears relatively early in the collation sequence between the<space>and<tab>characters. So any character class range that includes both<space>and<tab>will fail.The exact behavior changes slightly depending on the Windows version. Windows 7 hangs indefinitely if 0xFF is included. XP doesn't hang, but it always fails to find a match, and occasionally prints the following error message - "The process tried to write to a nonexistent pipe."
I no longer have access to a Vista machine, so I haven't been able to test on Vista.
Regex bug:
.and[^anySet]can match End-Of-File
The regex.meta-character should only match any character other than<CR>or<LF>. There is a bug that allows it to match the End-Of-File if the last line in the file is not terminated by<CR>or<LF>. However, the.will not match an empty file.For example, a file named "test.txt" containing a single line of
x, without terminating<CR>or<LF>, will match the following:findstr /r x......... test.txtThis bug has been confirmed on XP and Win7.
The same seems to be true for negative character sets. Something like
[^abc]will match End-Of-File. Positive character sets like[abc]seem to work fine. I have only tested this on Win7.讨论(0) -
When several commands are enclosed in parentheses and there are redirected files to the whole block:
< input.txt ( command1 command2 . . . ) > output.txt... then the files remains open as long as the commands in the block be active, so the commands may move the file pointer of the redirected files. Both MORE and FIND commands move the Stdin file pointer to the beginning of the file before process it, so the same file may be processed several times inside the block. For example, this code:
more < input.txt > output.txt more < input.txt >> output.txt... produce the same result than this one:
< input.txt ( more more ) > output.txtThis code:
find "search string" < input.txt > matchedLines.txt find /V "search string" < input.txt > unmatchedLines.txt... produce the same result than this one:
< input.txt ( find "search string" > matchedLines.txt find /V "search string" > unmatchedLines.txt )FINDSTR is different; it does not move the Stdin file pointer from its current position. For example, this code insert a new line after a search line:
call :ProcessFile < input.txt goto :EOF :ProcessFile rem Read the next line from Stdin and copy it set /P line= echo %line% rem Test if it is the search line if "%line%" neq "search line" goto ProcessFile rem Insert the new line at this point echo New line rem And copy the rest of lines findstr "^" exit /BWe may make good use of this feature with the aid of an auxiliary program that allow us to move the file pointer of a redirected file, as shown in this example.
This behavior was first reported by jeb at this post.
EDIT 2018-08-18: New FINDSTR bug reported
The FINDSTR command have a strange bug that happen when this command is used to show characters in color AND the output of such a command is redirected to CON device. For details on how use FINDSTR command to show text in color, see this topic.
When the output of this form of FINDSTR command is redirected to CON, something strange happens after the text is output in the desired color: all the text after it is output as "invisible" characters, although a more precise description is that the text is output as black text over black background. The original text will appear if you use COLOR command to reset the foreground and background colors of the entire screen. However, when the text is "invisible" we could execute a SET /P command, so all characters entered will not appear on the screen. This behavior may be used to enter passwords.
@echo off setlocal set /P "=_" < NUL > "Enter password" findstr /A:1E /V "^$" "Enter password" NUL > CON del "Enter password" set /P "password=" cls color 07 echo The password read is: "%password%"讨论(0)
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