Ubuntu – How to delete lines from a file until a specific pattern

command linetext processing

I need to look up the line number of a specific match in a file – email address – and then delete it from the beginning of the file until the matched line.

e.g Let's say the line number is 13807. So I need to keep the 13808+ lines intact.

Here's an example:

$ cat input
some
lines
before
mail@server.com
and
some
more
afterwards

$ cat output
and
some
more
afterwards

Best Answer

sed

sed '1,/mail@server\.com/d'  # excluding the matched line
sed '/mail@server\.com/,$!d' # including the matched line

Explanations

1,/mail@server\.com/d – delete every line from line 1 to (,) mail@server.com
/mail@server\.com/,$!d – don't (!) delete every line from mail@server.com to (,) the end of the file ($), but everything else

Usage

sed '…' file > file2 # save output in file2
sed -i.bak '…' file  # alter file in-place saving a backup as file.bak
sed -i '…' file      # alter file in-place without backup (caution!)

awk

awk 'f;/mail@server\.com/{f=1}' # excluding the matched line
awk '/mail@server\.com/{f=1}f'  # including the matched line

Explanations

f – variable f, variables are 0 = false by default, awk prints nothing if the expression is false and just prints the line if the expression is true
/mail@server\.com/{f=1} – if mail@server.com is found set f=1, therefore rendering the whole expression true the next time f occurs in the expression

Usage

awk '…' file > file2                          # save output in file2
awk -iinplace -vINPLACE_SUFFIX=.bak '…' file  # alter file in-place saving a backup as file.bak
awk -iinplace '…' file                        # alter file in-place without backup (caution!)

Explanation

0777 : -0 sets sets the input record separator (perl special variable $/ which is a newline by default). Setting this to a value greater than 0400 will cause Perl to slurp the entire input file into memory.
pe : the -p means "print each input line after applying the script given by -e to it".
$_=$_ x 1000 : $_ is the current input line. Since we're reading the entire file at once because of -0700, this means the entire file. The x 1000 will result in 1000 copies of the entire file being printed.

Ubuntu – How to delete numbered files in a given range

Assuming you know or can guess the end of the range, you could use brace expansions:

rm a_{000750..000850}

The above will delete the 101 files between a_000750 and a_000850 inclusive (and complain about filenames that refer to non-existing files). If you have too many files for that, use find:

find . -name 'a_*' | while read file; do 
  [ "${file#./a_}" -gt 000749 ] && rm -v "$file" 
done

Here, the find simply lists all files matching a_*. The list is passed to a while loop where each file name is read into the variable $file. Then, using bash's string manipulation features, if the numerical part (find prints files as ./file, so ${file#./a_} prints the number only) is 000750 or greater, the file is deleted. The -v is just there so you can see what files were removed.

Note that the above assumes sane file names. If your names can have spaces, newlines or other weird characters, use this instead:

find . -name 'a_*' -print0 | while IFS= read -rd '' file; do 
  [ "${file#./a_}" -gt 000749 ] && rm -v "$file" 
done

Best Answer

sed

Explanations

Usage

awk

Explanations

Usage

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