Delete text starting from a determinated string

Question

For example, if a have the following text in a file on my Linux system:

10-02-2020
given as file name) for lines containing a match to the given PATTERN. By default, grep prints the matching lines.
In addition, two variant programs egrep and fgrep are available. egrep is the same as grep -E. fgrep is the same as grep -F
16-02-2020
The top program provides a dynamic real-time view of a running
       system.  It can display system summary information as well as a list
       of processes or threads currently being managed by the Linux kernel.
       The types of system summary information shown and the types, order
       and size of information displayed for processes are all user
       configurable and that configuration can be made persistent across
       restarts.

How can I delete all text before 16-02-2020 and turn the file into this:

16-02-2020
The top program provides a dynamic real-time view of a running
       system.  It can display system summary information as well as a list
       of processes or threads currently being managed by the Linux kernel.
       The types of system summary information shown and the types, order
       and size of information displayed for processes are all user
       configurable and that configuration can be made persistent across
       restarts.

Answer 1

You can do this with sed. The general format is:

sed -n '/pattern1/,/pattern2/p' file

The -n causes sed not to print unless explicitly told to with p. Som that command will print all lines that fall between a line matching pattern1 and one matching pattern2 (inclusive). If there are multiple matches, multiple lines will be printed.

In your case, you want to print everything until the end of the file, so pattern2 will be $. Therefore, you're looking for this:

$ sed -n '/16-02-2020/,$p' file
16-02-2020
The top program provides a dynamic real-time view of a running
   system.  It can display system summary information as well as a list
   of processes or threads currently being managed by the Linux kernel.
   The types of system summary information shown and the types, order
   and size of information displayed for processes are all user
   configurable and that configuration can be made persistent across
   restarts.

---

On an unrelated note, fgrep and egrep are deprecated, you should use grep -F and grep -E. See man grep:

In addition, the variant programs egrep and fgrep are the same as grep -E and grep -F, respectively. These variants are deprecated, but are provided for backward compatibility.

Answer 2

Perl version :

perl -ne '$f=1 if /16-02-2020/; print if $f' file

Answer 3

For pruning a block from a file, I think ed, which treats the file as a whole instead of acting on a line at a time the way sed does is a better choice:

$ ed -s input.txt
1,/^16-02-2020/-1d
wq
$ cat input.txt
16-02-2020
The top program provides a dynamic real-time view of a running
       system.  It can display system summary information as well as a list
       of processes or threads currently being managed by the Linux kernel.
       The types of system summary information shown and the types, order
       and size of information displayed for processes are all user
       configurable and that configuration can be made persistent across
       restarts.

Deletes everything from the first line to the line before the one starting with 16-02-2020 and saves the modified file. If used in a script you can use a heredoc to send commands to ed:

ed -s input.txt <<EOF
1,/^16-02-2020/-1d
w
EOF