operating system – Page 6

sample session using “variable expansion” with Bash shell

$com=world $echo com com $echo $com world $x=hello $echo ${x}{com} hello{com} $echo ${x}${com} helloworld $echo $x$com helloworld $echo ${x}world helloworld $echo ${x} world hello world $echo $x world hello world $echo $xcom $echo $x com hello com $echo $x $com hello world $echo $x$com helloworld $echo $xcom $echo ${x}com hellocom $ $your_id=${USER}-on-${HOSTNAME} $echo “$your_id” jeffrin-on-debian …

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sample session about “brace and tilde” expansions in Bash

$ls trueangle $echo hello > a.txt $echo killo > b.txt $cat {a,b}.txt hello killo $pwd /home/jeffrin/temp $cd ~ $pwd /home/jeffrin $cd tr trueangle/ trueangle.old/ $pwd /home/jeffrin $cd – /home/jeffrin/temp $pwd /home/jeffrin/temp $ls a.txt b.txt trueangle $

sample session about “alias expansion” in Bash

$ls -l 1 ls: cannot access ‘1’: No such file or directory $cat >> 1 hello $ls -l 1 -rw-r–r– 1 jeffrin jeffrin 6 Mar 20 23:38 1 $cat 1 hello $alias appendinput=”cat >>” $appendinput bash: syntax error near unexpected token `newline’ $appendinput app added $cat app added $

sample session with a bash shell expansion named “history expansion”

$! 1 bash: 1: command not found $!1 bash: !1: event not found $!+1 bash: !+1: event not found $!-1 ! 1 bash: 1: command not found $!! ! 1 bash: 1: command not found $!-0 bash: !-0: event not found $

getting choices listed directly with the first TAB

$p Display all 428 possibilities? (y or n) $p bash: p: command not found $cat .inputrc set show-all-if-ambiguous on $ related text: Specifies the duration Readline will wait for a character when reading an ambiguous key sequence (one that can form a complete key sequence using the input read so far, or can take additional …

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enclose one or more commands inside a pair of parentheses

$ls 1 $( ls date ) ls: cannot access date: No such file or directory $( `ls` date ) bash: 1: command not found $cat 1 B$ $( ls `date` ) ls: cannot access Mon: No such file or directory ls: cannot access Feb: No such file or directory ls: cannot access 22: No such …

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sample interaction with bash shell from the GNU project

$echo $BASH /bin/bash $echo $BASH_ $echo $BASH_v $echo $BASH_VERSION 4.3.42(1)-release $date || time Sun Feb 21 23:15:50 IST 2016 $datei || time bash: datei: command not found real 0m0.000s user 0m0.000s sys 0m0.000s $dateno || time bash: dateno: command not found real 0m0.000s user 0m0.000s sys 0m0.000s $time || date bash: syntax error near unexpected …

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the need of a command named “builtin”

$builtin echo jeffrin jeffrin $echo jeffrin jeffrin $echo() { echo “hi”; }; $echo jeffrin ^C $builtin echo jeffrin jeffrin $echo jeffrin ^C $ https://en.wikipedia.org/wiki/Shell_builtin http://unix.stackexchange.com/questions/11454/what-is-the- difference-between-a-builtin-command-and-one-that-is-not (jeffrin) what is the use of the command named “builtin” (jeffrin) llua : hello (llua) to avoid a possible wrapper

sample session involving “env” and “unset” commands

ABOUT env env is a shell command for Unix and Unix-like operating systems. It is used to either print a list of environment variables or run another utility in an altered environment without having to modify the currently existing environment. Using env, variables may be added or removed, and existing variables may be changed by …

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simple hack using the “join” command

$cat name.txt 1 ram 2 shyam 3 raju 4 biju $cat company.txt 1 google 2 facebook 3 twitter 4 ibm $join company.txt name.txt 1 google ram 2 facebook shyam 3 twitter raju 4 ibm biju $join name.txt company.txt 1 ram google 2 shyam facebook 3 raju twitter 4 biju ibm $