Bash

Bash: grep: A couple of usefull applications

19 November 2011 in Bash / GNU/Linux / HowTos tagged bash / delete / extract / GNU/Linux / grep / howtos by Tux

(How) to delete all empty lines from a file:

cat someFile | grep -v '^$'

(How) to get all numbers that have no sign in front of them (all positive numbers, from a file where on each line there is one number only):

cat someFile | grep ^[0-9]

(How) to extract all negative numbers (from a file where on each line there is one number only):
You can of course replace the minus ‘-‘ character with any other you want to use as a starting character for a line.

cat someFile | grep ^-

Bash: tr: A couple of usefull applications

19 November 2011 in Bash / GNU/Linux / HowTos tagged bash / character / delete / GNU/Linux / howtos / replace / tr by Tux

(How) to delete all instances of a character from a file:
The following example deletes all instances of the character ‘v’

cat someFile | tr -d v

(How) to replace all instances of a character with another:
The following example replaces all space characters with the new line character

cat someFile | tr ' ' '\n'

Bash: head: Remove last N lines from file 4

18 November 2011 in Bash / GNU/Linux / HowTos tagged bash / GNU/Linux / howtos / line / lines / tail by Tux

head -n -$N inputFile > outputFile

Where $N is the number of the line from the end which you want to stop printing.
For example if you want to delete the last line you must issue the following:

head -n -1 inputFile > outputFile

Bash: tail: Remove first N lines from file