I regularly have to move scripts between Windows and Linux systems. The line endings from
Windows can make running my scripts on Linux fail. I have been on a few systems where the
dos2unix command was not available, so how do I get rid of the Ctrl-M at the end of the lines?

Command: vi -b <filename>

The -b sets vi into binary mode. This displays the extra control characters. In vi, I remove the
ctrl-Ms.

In vi, I use the following key sequence in command mode:

 :%s/<ctrl-v><enter>//g 

The ctrl-v tells vi to take the next character and display it as a ctrl char sequence. And hitting the
enter key displays the ctrl-M. The :%s///g is a command to replace the characters in the first // and replace
it with the chars in the second // and the g says to do it to every line.

The other day I had to write a script to change to a working directory and back to the original directory. The problem was they were on different drives on Windows. So I had to find a way to capture the drive letter
and switch back to that drive. When using the following command,

cd F:somedir

you are not moved to the “F:” drive without an explicit “F:” command.

The cd Command on windows will show the current directory location. Using some string manipulation on that and capturing it to a variable allows us to go back to that drive.

REM Capture the current drive letter
set ORIGDRIVE=%cd:~0,2%

F:
REM some other scripting things here

REM Return to the original drive letter
ORIGDRIVE

The first line captures the current drive letter by specifying the first character with 0 and the ,2 states to pick up the next 2 characters which would hold the “C:” or whatever drive you started on.

Tags: BAT, DOS, scripting, Windows

I had to write a backup script the other day and used the find command to find the files that were older than a given amount of days.

DAYS_TO_KEEP=7
find /path/to/files* -type f -name *.bak -mtime $DAYS_TO_KEEP -exec rm {} ;

The -name argument uses the escaped asterisk so command completion does not replace it with all the file names.

The -mtime argument takes a number that is the number of days to look at.

The -exec argument takes a command and the {} is replaced with the current file name and the ; is the end of the command.

This is a small part of the power of the find command.