commandline session
$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
$
Bash . Running Several Commands All at Once
commandline session
$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 $
input redirection indicated by < character
commandline session
$cat bash.txt hack hacker $cat < bash.txt hack hacker $wc < bash.txt 2 2 12 $wc -l yab.txt $cat yab.txt hello $wc < yab.txt 1 1 6 $
Basic tinkering with “set” command and “noclobber” related
commandline session
[bash light=”true”]
$echo improve > clean.txt
$cat clean.txt
improve
$set -o noclobber
$echo new > clean.txt
bash: clean.txt: cannot overwrite existing file
$echo new >> clean.txt
$cat clean.txt
improve
new
$echo again >| clean.txt
$cat clean.txt
again
$set +o noclobber
$echo improve > clean.txt
$cat clean.txt
improve
$
[/bash]
Bash . set -o noclobber . environment manipulation
commandline session
$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 Query Terminfo Database
commandline session
$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
$
$
Grouping Output from several commands
commandline session
$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
$
Errors and Exceptions
commandline session
$gcc error.c
$cat error.c
#include
main()
{
int a=0;
int b=10;
printf("Hello Alln");
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
pattern matching operators PART 1
commandline session
$cat pm.sh
#!/bin/bash
filename=${1##*/}
echo $filename
$sh pm.sh /bin/bash
bash
$vim pm.sh
$cat pm.sh
#!/bin/bash
filename=${1}
echo $filename
$sh pm.sh /bin/bash
/bin/bash
$vim pm.sh
$cat pm.sh
#!/bin/bash
filename=${#}
echo $filename
$sh pm.sh /bin/bash
1
$vim pm.sh
$cat pm.sh
#!/bin/bash
filename=${##}
echo $filename
$sh pm.sh /bin/bash
1
$vim pm.sh
$cat pm.sh
#!/bin/bash
filename=${*}
echo $filename
$sh pm.sh /bin/bash
/bin/bash
$vim pm.sh
$cat pm.sh
#!/bin/bash
filename=${/}
echo $filename
$sh pm.sh /bin/bash
pm.sh: 3: pm.sh: Bad substitution
$
Bash . number of script arguments
commandline session
$. var 1 2 3 4 4 $. var 1 2 3 4 3 3 3 7 $cat var Name=Jeffrin Age=36 echo $# $. var 0 $. var . 1 $. var $ 1 $. var ? 5 $. var ? 5 $. var 1 2 2 $. var ? 5 $echo $? 0 $. var * 768 $. var ) bash: syntax error near unexpected token `)' $. var & [1] 5679 $0 [1]+ Done . var $. var ^ 1 $. var % 1 $. var @ 1 $. var ! 1 $. var ~ 1 $. var - 1 $. var _ 1 $. var + 1 $. var = 1 $. var | > ; bash: syntax error near unexpected token `;' $. var > . 1 $ $. var ? ~/ 0/ 1 c h $. var ? 5 $. var * Display all 768 possibilities? (y or n) $. var * 768 $