Bash

Configuring your environment variables: .bashrc

> vim ~/.bashrc
# .bashrc

# Source global definitions
if [ -f /etc/bashrc ]; then
    . /etc/bashrc
fi

# User specific aliases and functions
export PATH=\
./bin:\
/opt/local/bin:\
/opt/local/gnu/bin:\
/opt/local/gnome2/bin:\
/opt/local/gnome1/bin:\
/opt/local/mozilla/bin:\
/usr/local/netcdf/include:\
/usr/local/netcdf/lib:\
/usr/local/netcdf/bin:\
$PATH

export MANPATH=\
/opt/local/man:\
/opt/local/gnu/man:\
/opt/local/gnome2/man:\
/opt/local/gnome1/man:\
/opt/local/mozilla/man:\
$MANPATH

Flow control

While

Count=0
while test $Count -lt 10
do
	echo "Inside first loop $Count"

Count=`expr $Count + 1`

done
echo "Outside first loop $Count"

If

if [ $# -ne "$ARGS" ]; then
  echo "Description: Creates ring of tw bots"
  echo "Usage: > `basename $0` tw_ringof.txt"
  exit $E_BADARGS
fi

Case

case "$3" in
  'test')
    twitbot="pointptteste:pointpt"
    ;;
  *)
    twitbot="weather${city}:weather"
    ;;
esac

Examples

Find string in files

Using the Find is good under windows when one whishes to search for a string inside a set of files. But in linux one must rely on alternative routes. This example uses for, pipes, grep and cat and prints out any line matching MATCH from a list of files containing the FILEPATTERN pattern:

> for i in `find . | grep 'FILEPATTERN'`; do cat $i | grep MATCH;done

Now, if you want to change the MATCH pattern with a SUBST pattern, then check out Sed.

Replicate directories tree

In order to duplicate the directory tree simply type in bash inside the root of the directory to duplicate:

 > for i in `find . | grep '[^.]....$' | grep '[^.]...$' | grep '[^.]..$'`; do mkdir NEWROOT/$i; done

where NEWROOT is the new home directory of the duplicated directory tree.

Here's a more elegant way of doing the directory skeleton replication:

> for i in `find ROOT -type d | sed 's/ROOT/NEWROOT/g'`; do mkdir $i; done

Now you are able to transfer files between the original directory tree and the duplicated directory tree. You can transfer them one file at a time, or by extensions:

> for i in `find . | grep '\.SUFF$'`; do cp 

where SUFF is the file extension. (Remember to execute the command from within the original directory tree's root.)

Piping output

Here's one example that pipes the output of a program to the input of another program

> echo My Sister | (read a b; echo $a; echo$b)
My
Sister

Here's one example to mute the stdout and the stderr

> echo coucou >/dev/null 2>&1

Using if

> if [ `diff ${file}.txt ${file}.tmp | wc -l` -gt 0 ]; then echo Ok; fi

Reading and setting environment variables

This examples creates the environment variable $mess by reading the line from file.txt:

> read mess < file.txt

Manipulating variables

> ${var/pattern/replacement}

> let var = $othervar + 3

> ${var:3:2}

substring from 3-rd + 1 char with an offset of 2 char.

> ${#var}

returns the number of chars in $var

> ${var:0:${#var}-3}

substring everything except the last 3 chars

> ${var:-3}

substring only the last 3 chars

External References

• bash reference manual.