Questions[bash]

Question and answer based on my own question and answer in How to select lines between two patterns?

I have a file like the following and I would like to print the lines that appear between the patterns PAT1and PAT2.

1
2
PAT1
3    - primer bloque
4
PAT2
5
6
PAT1
7    - segundo bloque
PAT2
8
9
PAT1
10    - tercer bloque

I've read How to select lines between two marker patterns which may occur multiple times with awk/sed but I'm curious to see all the possible combinations, both printing the patterns and not.

How can I select the lines between two patterns?

I have to delete compressed files that are backups of our Database following the following two rules:

1. Must be more than 15 days old
2. Do not delete the backups of Sundays

I decided to use the command find, I think it is the most complete of the search commands (at least the ones I know of).

The first rule is simple, using the parameter -ctimeI can find files with a creation date older than 15 days:

$ find /backups/db/ -type f -ctime +15 -name "*.sql.gz" 
./gestagro_2015_11_01.sql.gz
./gestagro_2015_11_02.sql.gz
./gestagro_2015_11_03.sql.gz
(varios resultados)

Then, in the same findI did not find anything similar on your manpage regarding days of the week. The closest I've come so far is being able to print the filename along with its date formatted to display the day of the week using the action -printf:

$ find /backups/db/ -type f -ctime +15 -name "*.sql.gz" -printf "%p %Aa\n"
./gestagro_2015_11_01.sql.gz dom
./gestagro_2015_11_02.sql.gz lun
./gestagro_2015_11_03.sql.gz mar
(varios resultados)

The problem now is that I don't know how to filter those results again to pick those that are not of the day domand then apply the -delete.

I am open to new options, not necessarily with the command find, it may be using pipes or whatever works for this case. Help me see the light.

Update

@Gilles answer helped me find my way, however I had to modify the last part a bit. The final statement is as follows:

$ find /backups/db/ -type f -ctime +15 -printf '%p %Aa\n' | sed -e '/dom$/d' -e 's/ [^ ]+$//' | cut -d' ' -f1 | xargs rm

Until recently I used Bash. There, you can delete all the content of the line from where the cursor is to the beginning of the line by pressing Ctrl+ U.

$ hola que tal estas
          ^
$ tal estas            # Ctrl+U
  ^

And so the Bash manual in 8.4.4 Killing And Yanking says :

unix-line-discard (Cu)

Kill backward from the cursor to the beginning of the current line.

However, now I use zsh( Oh My Zsh specifically) and this functionality is gone. Now when I press Ctrl+ Uthe entire line is deleted. If I do Ctrl+ W, words are eliminated in the following way:

 $ hola que_tal estas
               ^
 $ hola que_ estas        # Ctrl+U
            ^
 $ hola  estas            # Ctrl+U
        ^

Does anyone know what I need to set so that Ctrl+U returns to delete everything from the cursor to the beginning of the line?

Let's say I have a file archivowith many lines, but I only want to print one particular line, say number n.

How can I achieve this using tools that are on a standard Linux system? The option head XX archivo | tail -Nseems impractical to me.

Suppose I'm in a directory and I know a file archivoexists:

if [ -f "archivo" ]; then
    echo "archivo existe"
fi

Is there a way to check if the file doesn't exist without using elsethis conditional?