grep -options（参数） pattern（关键词） files（文本文件）

grep [OPTION...] PATTERNS [FILE...]       
grep [OPTION...] -e PATTERNS ... [FILE...]      #匹配多个规则，（规则间的关系是：或）
grep [OPTION...] -f PATTERN_FILE ... [FILE...]  #从规则文件中匹配规则

├── grep_test.txt
├── hel.c
├── hello.c
└── hello.txt

#代理组配置
proxy-groups:
  - name: 测试
    type: "select"
    proxies: 
      -  T2
# 规则配置
rules:
  - DOMAIN-SUFFIX,google.com,测试
  - DOMAIN-SUFFIX,facebook.com,测试
  - DOMAIN-SUFFIX,youtube.com,测试
  - DOMAIN-SUFFIX,openai.com,测试
  - MATCH,final,测试
# # 其他配置
#  experimental：
#   ignore-resolve-fail: true

root@CQUPTLEI:~/Linux_test# grep -ni "com" grep_test.txt
11:  - DOMAIN-SUFFIX,google.com,测试
12:  - DOMAIN-SUFFIX,facebook.com,测试
13:  - DOMAIN-SUFFIX,youtube.com,测试
14:  - DOMAIN-SUFFIX,openai.com,测试

root@CQUPTLEI:~/Linux_test# grep -ni "\<测试\>" grep_test.txt
11:  - DOMAIN-SUFFIX,google.com,测试
12:  - DOMAIN-SUFFIX,facebook.com,测试
13:  - DOMAIN-SUFFIX,youtube.com,测试
14:  - DOMAIN-SUFFIX,openai.com,测试

root@CQUPTLEI:~/Linux_test# grep -l "true$" *
grep_test.txt

├── grep_test.txt
├── hel.c
├── hello.c
├── hello.txt
└── subdir
    └── sub.txt

subdir/sub.txt:2:youtube.com
root@CQUPTLEI:~/Linux_test# grep -rn  ".com" * 
grep_test.txt:11:  - DOMAIN-SUFFIX,google.com,测试
grep_test.txt:12:  - DOMAIN-SUFFIX,facebook.com,测试
grep_test.txt:13:  - DOMAIN-SUFFIX,youtube.com,测试
grep_test.txt:14:  - DOMAIN-SUFFIX,openai.com,测试
subdir/sub.txt:2:youtube.com

root@CQUPTLEI:~/Linux_test# grep -rn "测试" *
grep_test.txt:3:  - name: 测试
grep_test.txt:11:  - DOMAIN-SUFFIX,google.com,测试
grep_test.txt:12:  - DOMAIN-SUFFIX,facebook.com,测试
grep_test.txt:13:  - DOMAIN-SUFFIX,youtube.com,测试
grep_test.txt:14:  - DOMAIN-SUFFIX,openai.com,测试
grep_test.txt:15:  - MATCH,final,测试
subdir/sub.txt:4:测试

root@CQUPTLEI:~/Linux_test# grep -rn -e "测试" -e "true" *
grep_test.txt:3:  - name: 测试
grep_test.txt:11:  - DOMAIN-SUFFIX,google.com,测试
grep_test.txt:12:  - DOMAIN-SUFFIX,facebook.com,测试
grep_test.txt:13:  - DOMAIN-SUFFIX,youtube.com,测试
grep_test.txt:14:  - DOMAIN-SUFFIX,openai.com,测试
grep_test.txt:15:  - MATCH,final,测试
grep_test.txt:19:#   ignore-resolve-fail: true
subdir/sub.txt:4:测试

.com
[0-9]

root@CQUPTLEI:~/Linux_test# grep -rn -f rule.txt grep_test.txt
6:      -  T2
11:  - DOMAIN-SUFFIX,google.com,测试
12:  - DOMAIN-SUFFIX,facebook.com,测试
13:  - DOMAIN-SUFFIX,youtube.com,测试
14:  - DOMAIN-SUFFIX,openai.com,测试

root@CQUPTLEI:~/Linux_test# grep -w "测试" grep_test.txt >output.txt

GREP(1)                                                           User Commands                                                           GREP(1)
NAME
       grep, egrep, fgrep, rgrep - print lines that match patterns
SYNOPSIS
       grep [OPTION...] PATTERNS [FILE...]
       grep [OPTION...] -e PATTERNS ... [FILE...]
       grep [OPTION...] -f PATTERN_FILE ... [FILE...]
DESCRIPTION
       grep searches for PATTERNS in each FILE.  PATTERNS is one or more patterns separated by newline characters, and grep prints each line that
       matches a pattern.  Typically PATTERNS should be quoted when grep is used in a shell command.
       A FILE of “-” stands for standard input.  If no FILE is given, recursive searches examine the working directory, and nonrecursive searches
       read standard input.
       In  addition, the variant programs egrep, fgrep and rgrep are the same as grep -E, grep -F, and grep -r, respectively.  These variants are
       deprecated, but are provided for backward compatibility.
OPTIONS
   Generic Program Information
       --help Output a usage message and exit.
       -V, --version
              Output the version number of grep and exit.
   Pattern Syntax
       -E, --extended-regexp
              Interpret PATTERNS as extended regular expressions (EREs, see below).
       -F, --fixed-strings
              Interpret PATTERNS as fixed strings, not regular expressions.
       -G, --basic-regexp
              Interpret PATTERNS as basic regular expressions (BREs, see below).  This is the default.
       -P, --perl-regexp
              Interpret PATTERNS as Perl-compatible regular expressions  (PCREs).   This  option  is  experimental  when  combined  with  the  -z
              (--null-data) option, and grep -P may warn of unimplemented features.
   Matching Control
       -e PATTERNS, --regexp=PATTERNS
              Use  PATTERNS  as  the  patterns.  If this option is used multiple times or is combined with the -f (--file) option, search for all
              patterns given.  This option can be used to protect a pattern beginning with “-”.
       -f FILE, --file=FILE
              Obtain patterns from FILE, one per line.  If this option is used multiple times or is  combined  with  the  -e  (--regexp)  option,
              search for all patterns given.  The empty file contains zero patterns, and therefore matches nothing.
       -i, --ignore-case
              Ignore case distinctions in patterns and input data, so that characters that differ only in case match each other.
       --no-ignore-case
              Do  not  ignore  case  distinctions  in  patterns and input data.  This is the default.  This option is useful for passing to shell
              scripts that already use -i, to cancel its effects because the two options override each other.
       -v, --invert-match
              Invert the sense of matching, to select non-matching lines.
       -w, --word-regexp
              Select only those lines containing matches that form whole words.  The test is that the matching substring must either  be  at  the
              beginning  of  the  line,  or preceded by a non-word constituent character.  Similarly, it must be either at the end of the line or
              followed by a non-word constituent character.  Word-constituent characters are letters, digits, and the  underscore.   This  option
              has no effect if -x is also specified.
       -x, --line-regexp
              Select  only  those  matches  that exactly match the whole line.  For a regular expression pattern, this is like parenthesizing the
              pattern and then surrounding it with ^ and $.
       -y     Obsolete synonym for -i.
   General Output Control
       -c, --count
              Suppress normal output; instead print a count of matching lines for each input file.   With  the  -v,  --invert-match  option  (see
              below), count non-matching lines.
       --color[=WHEN], --colour[=WHEN]
              Surround  the  matched  (non-empty)  strings, matching lines, context lines, file names, line numbers, byte offsets, and separators
              (for fields and groups of context lines) with escape sequences to display them in color on the terminal.  The colors are defined by
              the  environment variable GREP_COLORS.  The deprecated environment variable GREP_COLOR is still supported, but its setting does not
              have priority.  WHEN is never, always, or auto.
       -L, --files-without-match
              Suppress normal output; instead print the name of each input file from which no output  would  normally  have  been  printed.   The
              scanning will stop on the first match.
       -l, --files-with-matches
              Suppress normal output; instead print the name of each input file from which output would normally have been printed.  The scanning
              will stop on the first match.
       -m NUM, --max-count=NUM
              Stop reading a file after NUM matching lines.  If the input is standard input from a regular  file,  and  NUM  matching  lines  are
              output,  grep  ensures that the standard input is positioned to just after the last matching line before exiting, regardless of the
              presence of trailing context lines.  This enables a calling process to resume a search.  When grep stops after NUM matching  lines,
              it  outputs any trailing context lines.  When the -c or --count option is also used, grep does not output a count greater than NUM.
              When the -v or --invert-match option is also used, grep stops after outputting NUM non-matching lines.
       -o, --only-matching
              Print only the matched (non-empty) parts of a matching line, with each such part on a separate output line.
       -q, --quiet, --silent
              Quiet; do not write anything to standard output.  Exit immediately with zero status if any match is found, even  if  an  error  was
              detected.  Also see the -s or --no-messages option.
       -s, --no-messages
              Suppress error messages about nonexistent or unreadable files.
   Output Line Prefix Control
       -b, --byte-offset
              Print  the  0-based  byte offset within the input file before each line of output.  If -o (--only-matching) is specified, print the
              offset of the matching part itself.
       -H, --with-filename
              Print the file name for each match.  This is the default when there is more than one file to search.
       -h, --no-filename
              Suppress the prefixing of file names on output.  This is the default when there is only  one  file  (or  only  standard  input)  to
              search.
       --label=LABEL
              Display  input actually coming from standard input as input coming from file LABEL.  This can be useful for commands that transform
              a file's contents before searching, e.g., gzip -cd foo.gz | grep --label=foo -H 'some pattern'.  See also the -H option.
       -n, --line-number
              Prefix each line of output with the 1-based line number within its input file.
       -T, --initial-tab
              Make sure that the first character of actual line content lies on a tab stop, so that the alignment of tabs looks normal.  This  is
              useful  with options that prefix their output to the actual content: -H,-n, and -b.  In order to improve the probability that lines
              from a single file will all start at the same column, this also causes the line number and byte offset (if present) to  be  printed
              in a minimum size field width.
       -u, --unix-byte-offsets
              Report  Unix-style  byte offsets.  This switch causes grep to report byte offsets as if the file were a Unix-style text file, i.e.,
              with CR characters stripped off.  This will produce results identical to running grep on a Unix machine.  This option has no effect
              unless -b option is also used; it has no effect on platforms other than MS-DOS and MS-Windows.
       -Z, --null
              Output  a  zero  byte  (the ASCII NUL character) instead of the character that normally follows a file name.  For example, grep -lZ
              outputs a zero byte after each file name instead of the usual newline.  This option makes  the  output  unambiguous,  even  in  the
              presence  of file names containing unusual characters like newlines.  This option can be used with commands like find -print0, perl
              -0, sort -z, and xargs -0 to process arbitrary file names, even those that contain newline characters.
   Context Line Control
       -A NUM, --after-context=NUM
              Print NUM lines of trailing context after matching lines.  Places a line containing  a  group  separator  (--)  between  contiguous
              groups of matches.  With the -o or --only-matching option, this has no effect and a warning is given.
       -B NUM, --before-context=NUM
              Print  NUM  lines  of  leading  context  before matching lines.  Places a line containing a group separator (--) between contiguous
              groups of matches.  With the -o or --only-matching option, this has no effect and a warning is given.
       -C NUM, -NUM, --context=NUM
              Print NUM lines of output context.  Places a line containing a group separator (--) between contiguous groups of matches.  With the
              -o or --only-matching option, this has no effect and a warning is given.
   File and Directory Selection
       -a, --text
              Process a binary file as if it were text; this is equivalent to the --binary-files=text option.
       --binary-files=TYPE
              If  a  file's  data  or metadata indicate that the file contains binary data, assume that the file is of type TYPE.  Non-text bytes
              indicate binary data; these are either output bytes that are improperly encoded for the current locale, or null  input  bytes  when
              the -z option is not given.
              By default, TYPE is binary, and grep suppresses output after null input binary data is discovered, and suppresses output lines that
              contain improperly encoded data.  When some output is suppressed, grep follows any output with a one-line  message  saying  that  a
              binary file matches.
              If  TYPE  is without-match, when grep discovers null input binary data it assumes that the rest of the file does not match; this is
              equivalent to the -I option.
              If TYPE is text, grep processes a binary file as if it were text; this is equivalent to the -a option.
              When type is binary, grep may treat non-text bytes as line terminators even without the -z  option.   This  means  choosing  binary
              versus text can affect whether a pattern matches a file.  For example, when type is binary the pattern q$ might match q immediately
              followed by a null byte, even though this is not matched when type is text.  Conversely, when type is binary the pattern . (period)
              might not match a null byte.
              Warning:  The  -a  option  might  output  binary  garbage, which can have nasty side effects if the output is a terminal and if the
              terminal driver interprets some of it as commands.  On the other hand, when reading files whose text encodings are unknown, it  can
              be  helpful  to  use  -a  or to set LC_ALL='C' in the environment, in order to find more matches even if the matches are unsafe for
              direct display.
       -D ACTION, --devices=ACTION
              If an input file is a device, FIFO or socket, use ACTION to process it.  By default, ACTION is read, which means that  devices  are
              read just as if they were ordinary files.  If ACTION is skip, devices are silently skipped.
       -d ACTION, --directories=ACTION
              If an input file is a directory, use ACTION to process it.  By default, ACTION is read, i.e., read directories just as if they were
              ordinary files.  If ACTION is skip, silently skip directories.  If  ACTION  is  recurse,  read  all  files  under  each  directory,
              recursively, following symbolic links only if they are on the command line.  This is equivalent to the -r option.
       --exclude=GLOB
              Skip  any  command-line file with a name suffix that matches the pattern GLOB, using wildcard matching; a name suffix is either the
              whole name, or a trailing part that starts with a non-slash character immediately after a slash (/) in the  name.   When  searching
              recursively,  skip  any subfile whose base name matches GLOB; the base name is the part after the last slash.  A pattern can use *,
              ?, and [...] as wildcards, and \ to quote a wildcard or backslash character literally.
       --exclude-from=FILE
              Skip files whose base name matches any of the  file-name  globs  read  from  FILE  (using  wildcard  matching  as  described  under
              --exclude).
       --exclude-dir=GLOB
              Skip  any  command-line  directory  with  a  name  suffix  that  matches  the  pattern  GLOB.  When searching recursively, skip any
              subdirectory whose base name matches GLOB.  Ignore any redundant trailing slashes in GLOB.
       -I     Process a binary file as if it did not contain matching data; this is equivalent to the --binary-files=without-match option.
       --include=GLOB
              Search only files whose base name matches GLOB (using wildcard matching as described under --exclude).
       -r, --recursive
              Read all files under each directory, recursively, following symbolic links only if they are on the command line.  Note that  if  no
              file operand is given, grep searches the working directory.  This is equivalent to the -d recurse option.
       -R, --dereference-recursive
              Read all files under each directory, recursively.  Follow all symbolic links, unlike -r.
   Other Options
       --line-buffered
              Use line buffering on output.  This can cause a performance penalty.
       -U, --binary
              Treat  the  file(s) as binary.  By default, under MS-DOS and MS-Windows, grep guesses whether a file is text or binary as described
              for the --binary-files option.  If grep decides the file is a text file, it  strips  the  CR  characters  from  the  original  file
              contents  (to  make regular expressions with ^ and $ work correctly).  Specifying -U overrules this guesswork, causing all files to
              be read and passed to the matching mechanism verbatim; if the file is a text file with CR/LF pairs at the end of  each  line,  this
              will cause some regular expressions to fail.  This option has no effect on platforms other than MS-DOS and MS-Windows.
       -z, --null-data
              Treat  input  and output data as sequences of lines, each terminated by a zero byte (the ASCII NUL character) instead of a newline.
              Like the -Z or --null option, this option can be used with commands like sort -z to process arbitrary file names.
REGULAR EXPRESSIONS
       A regular expression is a pattern that describes a set  of  strings.   Regular  expressions  are  constructed  analogously  to  arithmetic
       expressions, by using various operators to combine smaller expressions.
       grep  understands  three  different versions of regular expression syntax: “basic” (BRE), “extended” (ERE) and “perl” (PCRE).  In GNU grep
       there is no difference in available  functionality  between  basic  and  extended  syntaxes.   In  other  implementations,  basic  regular
       expressions  are  less  powerful.   The  following  description  applies  to  extended  regular expressions; differences for basic regular
       expressions are summarized afterwards.   Perl-compatible  regular  expressions  give  additional  functionality,  and  are  documented  in
       pcresyntax(3) and pcrepattern(3), but work only if PCRE is available in the system.
       The  fundamental  building  blocks  are the regular expressions that match a single character.  Most characters, including all letters and
       digits, are regular expressions that match themselves.  Any meta-character with special meaning may be  quoted  by  preceding  it  with  a
       backslash.
       The period . matches any single character.  It is unspecified whether it matches an encoding error.
   Character Classes and Bracket Expressions
       A  bracket  expression is a list of characters enclosed by [ and ].  It matches any single character in that list.  If the first character
       of the list is the caret ^ then it matches any character not in the list; it is unspecified whether it matches  an  encoding  error.   For
       example, the regular expression [0123456789] matches any single digit.
       Within  a  bracket  expression, a range expression consists of two characters separated by a hyphen.  It matches any single character that
       sorts between the two characters, inclusive, using the locale's collating sequence and character set.   For  example,  in  the  default  C
       locale,  [a-d]  is  equivalent  to  [abcd].  Many locales sort characters in dictionary order, and in these locales [a-d] is typically not
       equivalent to [abcd]; it might be equivalent to [aBbCcDd], for example.  To obtain the traditional interpretation of bracket  expressions,
       you can use the C locale by setting the LC_ALL environment variable to the value C.
       Finally, certain named classes of characters are predefined within bracket expressions, as follows.  Their names are self explanatory, and
       they are [:alnum:], [:alpha:], [:blank:], [:cntrl:], [:digit:], [:graph:], [:lower:],  [:print:],  [:punct:],  [:space:],  [:upper:],  and
       [:xdigit:].   For  example, [[:alnum:]] means the character class of numbers and letters in the current locale.  In the C locale and ASCII
       character set encoding, this is the same as [0-9A-Za-z].  (Note that the brackets in these class names are part of the symbolic names, and
       must  be  included in addition to the brackets delimiting the bracket expression.)  Most meta-characters lose their special meaning inside
       bracket expressions.  To include a literal ] place it first in the list.  Similarly, to include a literal ^ place it anywhere  but  first.
       Finally, to include a literal - place it last.
   Anchoring
       The caret ^ and the dollar sign $ are meta-characters that respectively match the empty string at the beginning and end of a line.
   The Backslash Character and Special Expressions
       The  symbols  \< and \> respectively match the empty string at the beginning and end of a word.  The symbol \b matches the empty string at
       the edge of a word, and \B matches the empty string provided it's not at the edge of a word.  The symbol \w is a synonym for  [_[:alnum:]]
       and \W is a synonym for [^_[:alnum:]].
   Repetition
       A regular expression may be followed by one of several repetition operators:
       ?      The preceding item is optional and matched at most once.
       *      The preceding item will be matched zero or more times.
       +      The preceding item will be matched one or more times.
       {n}    The preceding item is matched exactly n times.
       {n,}   The preceding item is matched n or more times.
       {,m}   The preceding item is matched at most m times.  This is a GNU extension.
       {n,m}  The preceding item is matched at least n times, but not more than m times.
   Concatenation
       Two  regular  expressions  may be concatenated; the resulting regular expression matches any string formed by concatenating two substrings
       that respectively match the concatenated expressions.
   Alternation
       Two regular expressions may be joined by the infix operator |; the  resulting  regular  expression  matches  any  string  matching  either
       alternate expression.
   Precedence
       Repetition  takes  precedence  over concatenation, which in turn takes precedence over alternation.  A whole expression may be enclosed in
       parentheses to override these precedence rules and form a subexpression.
   Back-references and Subexpressions
       The back-reference \n, where n is a single digit, matches the substring previously matched by the nth parenthesized subexpression  of  the
       regular expression.
   Basic vs Extended Regular Expressions
       In basic regular expressions the meta-characters ?, +, {, |, (, and ) lose their special meaning; instead use the backslashed versions \?,
       \+, \{, \|, \(, and \).
EXIT STATUS
       Normally the exit status is 0 if a line is selected, 1 if no lines were selected, and 2 if an error  occurred.   However,  if  the  -q  or
       --quiet or --silent is used and a line is selected, the exit status is 0 even if an error occurred.
ENVIRONMENT
       The behavior of grep is affected by the following environment variables.
       The  locale  for category LC_foo is specified by examining the three environment variables LC_ALL, LC_foo, LANG, in that order.  The first
       of these variables that is set specifies the locale.  For example, if LC_ALL is not set,  but  LC_MESSAGES  is  set  to  pt_BR,  then  the
       Brazilian Portuguese locale is used for the LC_MESSAGES category.  The C locale is used if none of these environment variables are set, if
       the locale catalog is not installed, or if grep was not compiled with national language support (NLS).  The shell command locale -a  lists
       locales that are currently available.
       GREP_OPTIONS
              This  variable  specifies  default  options  to  be  placed in front of any explicit options.  As this causes problems when writing
              portable scripts, this feature will be removed in a future release of grep, and grep warns if it is used.  Please use an  alias  or
              script instead.
       GREP_COLOR
              This  variable specifies the color used to highlight matched (non-empty) text.  It is deprecated in favor of GREP_COLORS, but still
              supported.  The mt, ms, and mc capabilities of GREP_COLORS have priority over it.  It can only specify the color used to  highlight
              the  matching  non-empty  text  in any matching line (a selected line when the -v command-line option is omitted, or a context line
              when -v is specified).  The default is 01;31, which means a bold red foreground text on the terminal's default background.
       GREP_COLORS
              Specifies the colors and other attributes used to highlight various parts of the output.  Its value is a  colon-separated  list  of
              capabilities  that  defaults  to  ms=01;31:mc=01;31:sl=:cx=:fn=35:ln=32:bn=32:se=36 with the rv and ne boolean capabilities omitted
              (i.e., false).  Supported capabilities are as follows.
              sl=    SGR substring for whole selected lines (i.e., matching lines when the -v command-line option  is  omitted,  or  non-matching
                     lines  when  -v  is  specified).  If however the boolean rv capability and the -v command-line option are both specified, it
                     applies to context matching lines instead.  The default is empty (i.e., the terminal's default color pair).
              cx=    SGR substring for whole context lines (i.e., non-matching lines when the -v command-line  option  is  omitted,  or  matching
                     lines  when  -v  is  specified).  If however the boolean rv capability and the -v command-line option are both specified, it
                     applies to selected non-matching lines instead.  The default is empty (i.e., the terminal's default color pair).
              rv     Boolean value that reverses (swaps) the meanings of the sl=  and  cx=  capabilities  when  the  -v  command-line  option  is
                     specified.  The default is false (i.e., the capability is omitted).
              mt=01;31
                     SGR  substring  for  matching  non-empty text in any matching line (i.e., a selected line when the -v command-line option is
                     omitted, or a context line when -v is specified).  Setting this is equivalent to setting both ms= and mc=  at  once  to  the
                     same value.  The default is a bold red text foreground over the current line background.
              ms=01;31
                     SGR  substring  for  matching  non-empty  text  in  a  selected line.  (This is only used when the -v command-line option is
                     omitted.)  The effect of the sl= (or cx= if rv) capability remains active when this kicks in.  The default  is  a  bold  red
                     text foreground over the current line background.
              mc=01;31
                     SGR  substring  for  matching  non-empty  text  in  a  context  line.  (This is only used when the -v command-line option is
                     specified.)  The effect of the cx= (or sl= if rv) capability remains active when this kicks in.  The default is a  bold  red
                     text foreground over the current line background.
              fn=35  SGR  substring  for  file  names  prefixing  any content line.  The default is a magenta text foreground over the terminal's
                     default background.
              ln=32  SGR substring for line numbers prefixing any content line.  The default is a  green  text  foreground  over  the  terminal's
                     default background.
              bn=32  SGR  substring  for  byte  offsets  prefixing  any content line.  The default is a green text foreground over the terminal's
                     default background.
              se=36  SGR substring for separators that are inserted between selected line fields (:),  between  context  line  fields,  (-),  and
                     between  groups  of  adjacent  lines when nonzero context is specified (--).  The default is a cyan text foreground over the
                     terminal's default background.
              ne     Boolean value that prevents clearing to the end of line using Erase in Line (EL) to Right (\33[K) each time a colorized item
                     ends.   This  is  needed  on  terminals  on  which  EL  is not supported.  It is otherwise useful on terminals for which the
                     back_color_erase (bce) boolean terminfo capability does not apply, when the  chosen  highlight  colors  do  not  affect  the
                     background, or when EL is too slow or causes too much flicker.  The default is false (i.e., the capability is omitted).
              Note that boolean capabilities have no =... part.  They are omitted (i.e., false) by default and become true when specified.
              See  the  Select  Graphic  Rendition  (SGR) section in the documentation of the text terminal that is used for permitted values and
              their meaning as character attributes.  These substring values are integers in decimal representation and can be concatenated  with
              semicolons.   grep  takes  care  of  assembling  the  result into a complete SGR sequence (\33[...m).  Common values to concatenate
              include 1 for bold, 4 for underline, 5 for blink, 7 for inverse, 39 for default foreground color, 30 to 37 for  foreground  colors,
              90 to 97 for 16-color mode foreground colors, 38;5;0 to 38;5;255 for 88-color and 256-color modes foreground colors, 49 for default
              background color, 40 to 47 for background colors, 100 to 107 for 16-color mode  background  colors,  and  48;5;0  to  48;5;255  for
              88-color and 256-color modes background colors.
       LC_ALL, LC_COLLATE, LANG
              These  variables  specify  the  locale for the LC_COLLATE category, which determines the collating sequence used to interpret range
              expressions like [a-z].
       LC_ALL, LC_CTYPE, LANG
              These variables specify the locale for the LC_CTYPE category, which determines the type of characters, e.g., which  characters  are
              whitespace.   This category also determines the character encoding, that is, whether text is encoded in UTF-8, ASCII, or some other
              encoding.  In the C or POSIX locale, all characters are encoded as a single byte and every byte is a valid character.
       LC_ALL, LC_MESSAGES, LANG
              These variables specify the locale for the LC_MESSAGES category, which determines the language that grep uses  for  messages.   The
              default C locale uses American English messages.
       POSIXLY_CORRECT
              If  set,  grep  behaves  as POSIX requires; otherwise, grep behaves more like other GNU programs.  POSIX requires that options that
              follow file names must be treated as file names; by default, such options are permuted to the front of the  operand  list  and  are
              treated  as  options.   Also,  POSIX  requires  that  unrecognized options be diagnosed as “illegal”, but since they are not really
              against the law the default is  to  diagnose  them  as  “invalid”.   POSIXLY_CORRECT  also  disables  _N_GNU_nonoption_argv_flags_,
              described below.
       _N_GNU_nonoption_argv_flags_
              (Here  N  is  grep's  numeric process ID.)  If the ith character of this environment variable's value is 1, do not consider the ith
              operand of grep to be an option, even if it appears to be one.  A shell can put this variable in the environment for  each  command
              it  runs, specifying which operands are the results of file name wildcard expansion and therefore should not be treated as options.
              This behavior is available only with the GNU C library, and only when POSIXLY_CORRECT is not set.
NOTES
       This man page is maintained only fitfully; the full documentation is often more up-to-date.
COPYRIGHT
       Copyright 1998-2000, 2002, 2005-2020 Free Software Foundation, Inc.
       This is free software; see the source for copying conditions.  There is NO warranty;  not  even  for  MERCHANTABILITY  or  FITNESS  FOR  A
       PARTICULAR PURPOSE.
BUGS
   Reporting Bugs
       Email bug reports to the bug-reporting address ⟨bug-grep@gnu.org⟩.  An email archive ⟨https://lists.gnu.org/mailman/listinfo/bug-grep⟩ and
       a bug tracker ⟨https://debbugs.gnu.org/cgi/pkgreport.cgi?package=grep⟩ are available.
   Known Bugs
       Large repetition counts in the {n,m} construct may cause grep to use lots of memory.  In addition, certain other obscure  regular  expres‐
       sions require exponential time and space, and may cause grep to run out of memory.
       Back-references are very slow, and may require exponential time.
EXAMPLE
       The following example outputs the location and contents of any line containing “f” and ending in “.c”, within all files in the current di‐
       rectory whose names contain “g” and end in “.h”.  The -n option outputs line numbers, the -- argument treats expansions of “*g*.h”  start‐
       ing  with “-” as file names not options, and the empty file /dev/null causes file names to be output even if only one file name happens to
       be of the form “*g*.h”.
         $ grep -n -- 'f.*\.c$' *g*.h /dev/null
         argmatch.h:1:/* definitions and prototypes for argmatch.c
       The only line that matches is line 1 of argmatch.h.  Note that the regular expression syntax used in the pattern differs from the globbing
       syntax that the shell uses to match file names.
SEE ALSO
   Regular Manual Pages
       awk(1),  cmp(1),  diff(1),  find(1),  perl(1),  sed(1),  sort(1),  xargs(1), read(2), pcre(3), pcresyntax(3), pcrepattern(3), terminfo(5),
       glob(7), regex(7).
   Full Documentation
       A complete manual ⟨https://www.gnu.org/software/grep/manual/⟩ is available.  If the info and grep programs are properly installed at  your
       site, the command
              info grep
       should give you access to the complete manual.
GNU grep 3.4                                                        2019-12-29                                                            GREP(1)