shell regular expression sample

re-simple.sh

bash$ cat textfile
This is line 1, of which there is only one instance.
 This is the only instance of line 2.
 This is line 3, another line.
 This is line 4.

bash$ grep 'the' textfile
This is line 1, of which there is only one instance.
 This is the only instance of line 2.
 This is line 3, another line.

bash$ grep '\' textfile
This is the only instance of line 2.

The only way to be certain that a particular RE works is to test it.

TEST FILE: tstfile                          # No match.
                                            # No match.
Run   grep "1133*"  on this file.           # Match.
                                            # No match.
                                            # No match.
This line contains the number 113.          # Match.
This line contains the number 13.           # No match.
This line contains the number 133.          # No match.
This line contains the number 1133.         # Match.
This line contains the number 113312.       # Match.
This line contains the number 1112.         # No match.
This line contains the number 113312312.    # Match.
This line contains no numbers at all.       # No match.

bash$ grep "1133*" tstfile
Run   grep "1133*"  on this file.           # Match.
 This line contains the number 113.          # Match.
 This line contains the number 1133.         # Match.
 This line contains the number 113312.       # Match.
 This line contains the number 113312312.    # Match.