Shell Command:grep. Match string by pattern.

On a file named a_file.txt, contents:
boot 

book

booze

machine

boots

bungie

bark

aardvark

broken$tuff

robots

basic reference:

grep options:

-n, --line-number         print line number with output lines

ex. grep -n "boo" a_file.txt

1:boot

2:book

3:booze

5:boots

-v, --invert-match        select non-matching lines

ex. grep -vn "boo" a_file.txt

4:machine

6:bungie

7:bark

8:aaradvark

9:robots

-c, --count               print only a count of selected lines per FILE

-A, --after-context=NUM   print NUM lines of trailing context
grep -A2 “mach” a_file.txt   #prin 2lines after matched machine line.
machine

boots

bungie

'grep -E' (also known as the egrep command) can using Extended regex for searching.

cat file.txt | grep -oE ".+\.properties"

jssp/platform/src/setup.properties  

jssp/platform/src/system/common/help/explanatory_notes.properties

jssp/platform/src/system/security/common/flash_menu_layout.properties

jssp/platform/src/system/security/common/flash_menu_pluginspage.properties

jssp/platform/src/system/setting/common/flash_setting_layout.properties

jssp/platform/src/system/setting/system/system_license/result.properties

jssp/src/init.propertie  s

 $ grep --help
Usage: grep [OPTION]... PATTERN [FILE]...
Search for PATTERN in each FILE.
Example: grep -i 'hello world' menu.h main.c
Pattern selection and interpretation:
  -E, --extended-regexp     PATTERN is an extended regular expression
  -F, --fixed-strings       PATTERN is a set of newline-separated strings ( it only searches for literal strings and not regexps.)
  -G, --basic-regexp        PATTERN is a basic regular expression (default)
  -P, --perl-regexp         PATTERN is a Perl regular expression
  -e, --regexp=PATTERN      use PATTERN for matching
  -f, --file=FILE           obtain PATTERN from FILE
  -i, --ignore-case         ignore case distinctions
  -w, --word-regexp         force PATTERN to match only whole words
  -x, --line-regexp         force PATTERN to match only whole lines
  -z, --null-data           a data line ends in 0 byte, not newline

Miscellaneous:
  -s, --no-messages         suppress error messages
  -v, --invert-match        select non-matching lines
  -V, --version             display version information and exit
      --help                display this help text and exit

Output control:
  -m, --max-count=NUM       stop after NUM selected lines
  -b, --byte-offset         print the byte offset with output lines
  -n, --line-number         print line number with output lines
      --line-buffered       flush output on every line
  -H, --with-filename       print file name with output lines
  -h, --no-filename         suppress the file name prefix on output
      --label=LABEL         use LABEL as the standard input file name prefix
  -o, --only-matching       show only the part of a line matching PATTERN
  -q, --quiet, --silent     suppress all normal output
      --binary-files=TYPE   assume that binary files are TYPE;
                            TYPE is 'binary', 'text', or 'without-match'
  -a, --text                equivalent to --binary-files=text
  -I                        equivalent to --binary-files=without-match
  -d, --directories=ACTION  how to handle directories;
                            ACTION is 'read', 'recurse', or 'skip'
  -D, --devices=ACTION      how to handle devices, FIFOs and sockets;
                            ACTION is 'read' or 'skip'
  -r, --recursive           like --directories=recurse
  -R, --dereference-recursive  likewise, but follow all symlinks
      --include=FILE_PATTERN  search only files that match FILE_PATTERN
      --exclude=FILE_PATTERN  skip files and directories matching FILE_PATTERN
      --exclude-from=FILE   skip files matching any file pattern from FILE
      --exclude-dir=PATTERN  directories that match PATTERN will be skipped.
  -L, --files-without-match  print only names of FILEs with no selected lines
  -l, --files-with-matches  print only names of FILEs with selected lines
  -c, --count               print only a count of selected lines per FILE
  -T, --initial-tab         make tabs line up (if needed)
  -Z, --null                print 0 byte after FILE name

Context control:
  -B, --before-context=NUM  print NUM lines of leading context
  -A, --after-context=NUM   print NUM lines of trailing context
  -C, --context=NUM         print NUM lines of output context
  -NUM                      same as --context=NUM
      --color[=WHEN],
      --colour[=WHEN]       use markers to highlight the matching strings;
                            WHEN is 'always', 'never', or 'auto'
  -U, --binary              do not strip CR characters at EOL (MSDOS/Windows)
When FILE is '-', read standard input.  With no FILE, read '.' if
recursive, '-' otherwise.  With fewer than two FILEs, assume -h.
Exit status is 0 if any line is selected, 1 otherwise;
if any error occurs and -q is not given, the exit status is 2.

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Examples of Using:
$ ls -l |awk '$5<=100 {print}' | grep -Ei 'ju\w'
drwxrwxr-x  3 eru eru       74 Jun 25  2019 doc
-rwxrw-r--  1 eru eru       66 Jul 30 15:26 precompile.sh
drwxrwxr-x  4 eru eru       41 Jun 25  2019 testdata

$grep -Eir '^\s*var\s+\w+'  $jsfolder  # grep by regexp from $jsfolder with recursive and ignore Case.

./main.html:        var textY = workfontsize - 11;

./main.html:  var anocanvas = document.getElementById(id);

...