$cat test.sh 
#!/usr/bin/env bash
# cookbook filename: checkfile
#
DIRPLACE=/tmp
INFILE=/home/jeffrin/amazing.data
OUTFILE=/home/jeffrin/more.results
if [ -d "$DIRPLACE" ]
then
cd $DIRPLACE
if [ -e "$INFILE" ]
then
if [ -w "$OUTFILE" ]
then
doscience < "$INFILE" >> "$OUTFILE"
else
echo "can not write to $OUTFILE"
fi
else
echo "can not read from $INFILE"
fi
else
echo "can not cd into $DIRPLACE"
fi

$sh test.sh 
can not read from /home/jeffrin/amazing.data
$> /home/jeffrin/amazing.data
$sh test.sh 
can not write to /home/jeffrin/more.results
$> /home/jeffrin/more.results
$sh test.sh 
test.sh: 14: test.sh: doscience: not found
$

related source : Bash CookBook

$cat hdoc.sh
#!/bin/bash

cat $1 <<EOF
EOF

 

$sh hdoc.sh bash.txt
hack
hacker
$
$cat bash.txt
hack
hacker
$vim hdoc.sh
$
$cat hdoc.sh
#!/bin/bash

grep $1 <<EOF
name jeffrin
age 36
sex male
EOF

$sh hdoc.sh 3
age 36
$

 

$cat loop.c 
main()
{
for (;;);
}

$./a.out 
^C
$nohup ./a.out 
nohup: ignoring input and appending output to `nohup.out'
^C
$cat nohup.out 
$ls nohup.out 
nohup.out
$

$ls
src  war
$cd & ls &
[1] 2587
[2] 2588
$src  war

[1]-  Done                    cd
[2]+  Done                    ls --color=auto
$pwd
/home/jeffrin/beautiful-work
$
$cd & ls & cd &
[1] 2590
[2] 2591
[3] 2592
$src  war

[1]   Done                    cd
[2]-  Done                    ls --color=auto
[3]+  Done                    cd
$pwd
/home/jeffrin/beautiful-work
$cd .. & pwd  &
[1] 2593
[2] 2594
$/home/jeffrin/beautiful-work

[1]-  Done                    cd ..
[2]+  Done                    pwd
$pwd
/home/jeffrin/beautiful-work
$cd &
[1] 2614
$pwd
/home/jeffrin/beautiful-work
[1]+  Done                    cd
$ls & cd ; pwd
[1] 2625
/home/jeffrin
$src  war

[1]+  Done                    ls --color=auto  (wd: ~/beautiful-work)
(wd now: ~)
$pwd
/home/jeffrin
$

$cat bash.txt 
hack
hacker
$cat < bash.txt 
hack
hacker
$wc < bash.txt 
 2  2 12
$wc -l  < bash.txt 
2
$cat bash.txt | wc
      2       2      12
$echo hello > yab.txt
$cat yab.txt 
hello
$wc < yab.txt 
1 1 6
$

$echo hello > bash.txt
$set -o noclobber
$echo hello > bash.txt
bash: bash.txt: cannot overwrite existing file
$echo hack > bash.txt
bash: bash.txt: cannot overwrite existing file
$echo hack >| bash.txt
$echo hack > bash.txt
bash: bash.txt: cannot overwrite existing file
$cat bash.txt 
hack
$echo hacker >>  bash.txt
$cat bash.txt 
hack
hacker
$echo hacker >  bash.txt
bash: bash.txt: cannot overwrite existing file
$cat bash.txt 
hack
hacker
$

$set -o noclobber
$ls a.out
a.out
$ls > a.out
bash: a.out: cannot overwrite existing file
$
$set +o noclobber
$
$ls > a.out
$rm a.out
$

$tput cup 3 4


    $tput cup 4  3
   $tput cols
140
$tput lines
39
$tput setb  4
$tput setb  `
> ^C
> ^C
$^C
$tput setb 0
$
$tput setb 1
$
$

        
$cd autotest/
$ls
autotest  cyclictest
${ ls ; pwd ; cd cyclictest ; ls ; pwd } > /tmp/all.out
> ^C
${ ls ; pwd ; cd cyclictest ; ls ; pwd ; } > /tmp/all.out
$cat /tmp/all.out 
autotest
cyclictest
/home/jeffrin/autotest
client.DEBUG
/home/jeffrin/autotest/cyclictest
$

$gcc error.c 
$cat error.c 
#include

main()
{
int a=0;
int b=10;
printf("Hello All\n");
printf("%d",b/a);
}

$./a.out > outputa
Floating point exception
$cat outputa 
$
$./a.out 2> outputa
Hello All
Floating point exception
$./a.out > outputa
Floating point exception
$./a.out 2> outputb
Hello All
Floating point exception
$./a.out &> outputc
Floating point exception
$cat outputa 
$
$cat outputb
$cat outputc 
$

An Error “indicates serious problems that a reasonable application should not try to catch.

An Exception “indicates conditions that a reasonable application might want to catch.

source : http://stackoverflow.com/questions/5813614/what-is-difference-between-errors-and-exceptions