Bash

One line infinite while loop

 in Bash / GNU/Linux / HowTos  tagged bash / GNU/Linux / howtos / infinite / one line / oneliner / while loop by 

while true; do echo 'Hit CTRL+C to exit'; someCommand; someOtherCommand; sleep 1; done

alternative syntax

while :; do echo 'Hit CTRL+C to exit'; someCommand; someOtherCommand; sleep 1; done

Bash: Read a file, line by line

 in Bash / GNU/Linux / HowTos  tagged bash / count / exec / GNU/Linux / howtos / line by

The following script will accept from the keyboard a filename, later it will read it and process it line by line.
In this example we will just number the lines, print them and count the total number of lines in the file.

#!/bin/sh
echo Enter the Filename to process
read filename
exec<$filename
lineNumber=0
while read line
do
	lineNumber=`expr $lineNumber + 1`;
	echo $lineNumber - $line;
done
echo "Total Lines Number: $lineNumber";

Remove leading characters/information from line using sed

 in Bash / GNU/Linux / HowTos  tagged bash / GNU/Linux / howtos / leading space / prefix / remove / sed by

Remove leading numbering from line

We had these log files that on most lines at the beginning there was a number followed by a dot and some times it had space characters.
The following sed command removes that prefix. and leaved intact the rest of the lines that do not have the prefix.

cat $log | sed '/^[0-9]*. */!d; s///;q';

e.g

Input: 123. Some text here.
Output:Some text here.

Remove leading whitespace (space and tabs) from line:

The following sed script will remove all leading whitespace from each line by using a regular expression to match space characters and tabs.

cat $log | sed 's/^[ t]*//';

e.g

Input:       Some text here.
Output:Some text here.