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Searching files using grep commands

The grep command is used to search the contents of a given file(s) for a pattern. It will display all lines of the file that contain the given search pattern.

The general format is:

$ grep [-v] [-i] [-E] _pattern_ _file1_ ...
  • -v : reverse the search. only show Non Matching lines.
  • -i : ignore case in comparing pattern to file contents.
  • -E : use regular expressions for matching patterns.
  • _pattern_ : search pattern.

Examples

Simple match

$ grep Alice input_users.txt
7:9876:Alice
7:54321:Alice

Case insensitive search

# no lines match lower-case "alice"
$ grep alice input_users.txt

$ grep -i alice input_users.txt
7:9876:Alice
7:54321:Alice

Reverse search

Show all lines that do not match the given pattern.

$ grep -v Alice input_users.txt
USER_ID:ACCT_NUM:USER_NAME
3:5555:David
5:789:Carol
...

Regular expression search

$ grep -E '(Frank|Alice)' input_users.txt
1:1234:Frank
7:9876:Alice
7:54321:Alice