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for loop

BASH Shell: For Loop File Names With Spaces

BASH for loop works nicely under UNIX / Linux / Windows and OS X while working on set of files. However, if you try to process a for loop on file name with spaces in them you are going to have some problem. For loop uses $IFS variable to determine what the field separators are. By default $IFS is set to the space character. There are multiple solutions to this problem.
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fold is really nifty command line utility to make a text file word wrap. This is useful for large number of text files processing. There is no need to write a perl / python code or use a word processor.

fold command syntax

fold -sw {COUNT} {input.txt} > {output.txt}

Wrap input lines in each input.txt, writing to standard output.txt.

Where,

  • -s: break at spaces
  • -w: {COUNT} use COUN} as WIDTH columns instead of default 80.

For example, following command will wrap input.txt at 60 width columns:
$ fold -sw 60 input.txt > output.txt

A large number of files can be processed using for shell loop:

for i in *.txt
do
  fold -sw 65 $i > $i.output
done

I've directory called /home/vivek/scripts/daily with over 25 perl / shell / python scripts for managing daily tasks. One day for some weird reason my crond died and I did not noticed the incident for 2 days.

Now crond is started and I'd like to run all those scripts. Here is a quick for loop running all scripts in a directory called ~/scripts/daily/:

for s in ~/scripts/daily/*;do [ -x $s ] && $s || : ;done

Above script will run each and every executable script it finds in a directory.

Update: As pointed out by jeff (see below), you can use run-parts shell script for the same purpose:
$ run-parts ~/scripts/daily/*

Installing software from a source code is common practice in UNIX and Linux world. Some time this is preferred method because it gives all power and flexibility you need to optimize your software such as MySQL, PHP, and Apache etc. However, uninstalling files installed from a source code tar ball is a big headache.

Two methods can be used to uninstall files:

Method # 1: make command

Use command make uninstall or equivalent supported command, Read INSTALL or README file in source code file to find out more about this method.

# make uninstall

Sure, this method sounds very easy but not supported by all tar balls.

Method # 2: find command

(a) Make a list of all files on the system before installing software i.e. a pre-installation list of all files on your system.

find /* > packgetlist.b4

(b) Now install the software (use configure & make to compile it)

make
make install

(c) Now make a list of all files on the system after installing software i.e. postinstall list

find /* > packagelist.after

(d) Next, compare both lists using the diff utility to find out what files are placing where. This list can be use to uninstall all files installed using source tar ball.
diff packagelist.b4 packagelist.after > package.uninstall.list

(e) After some time if you wish to uninstall files then you need to get list of files from package.uninstall.list file. Use following small for loop at shell prompt to remove all files:

for i in $(grep ">" package.uninstall.list | awk '{ print $2 }')
do
/bin/rm -fi $i
done

A note about binary packages

If you are using Debian / Ubuntu Linux, use following command to uninstall binary packages:
sudo apt-get remove {package-name}
If you are using Redhat / RHEL / Fedora / CentOS / Suse Linux, use following command to uninstall binary packages:
rpm -e {package-name}
OR
yum remove {package-name}