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=== three expression control loop === #!/bin/bash for (( c=1; c<=5; c++ )) do echo "Welcome $c times" done echo $1 exit 0 exit 0===Stopwatch=== <nowiki>BEGIN=$(date +%s)</nowiki> <nowiki></nowiki> <nowiki>echo Starting Stopwatch...</nowiki> <nowiki>echo Press Q to exit.</nowiki> <nowiki></nowiki> <nowiki>while true; do</nowiki> <nowiki> NOW=$(date +%s)</nowiki> <nowiki> let DIFF=$(($NOW - $BEGIN))</nowiki> <nowiki> let MINS=$(($DIFF / 60))</nowiki> <nowiki> let SECS=$(($DIFF % 60))</nowiki> <nowiki> let HOURS=$(($DIFF / 3600))</nowiki> <nowiki> let DAYS=$(($DIFF / 86400))</nowiki> <nowiki></nowiki> <nowiki> # \r is a "carriage return" - returns cursor to start of line</nowiki> <nowiki> printf "\r%3d Days, %02d:%02d:%02d" $DAYS $HOURS $MINS $SECS</nowiki> <nowiki></nowiki> <nowiki># In the following line -t for timeout, -N for just 1 character</nowiki> <nowiki> read -t 0.25 -N 1 input</nowiki> <nowiki> if [[ $input = "q" ]] || [[ $input = "Q" ]]; then</nowiki> <nowiki># The following line is for the prompt to appear on a new line.</nowiki> <nowiki> echo</nowiki> <nowiki> break </nowiki> <nowiki> fi</nowiki> <nowiki>done</nowiki>=== Press any key to continue === read -n 1 -s -r -p "Press any key to continue"=== DateTime Code === #!/bin/bash PDATE=`date '+%Y%m%d%H%M%S'` echo $PDATE=== Detach Command and Run in Background ===So if the terminal window is closed, the command continues to execute. You can append an "&" to the end of the command. This detaches the command from stdin. The & ampersand character is placed right of a space at the end of the command. Keep in mind that the command’s process is still managed by the shell and stdout and stderr are still attached. In some cases the process will be terminated if the shell session is closed. It depends on how the process was written.When you append the "&" at the end you are able to use the command prompt again, however, output from the process is displayed in the same terminal. You can redirect output to a text file or /dev/null. processname &> /dev/null &Now you have your command prompt back and will receive no messages, for the most part.To see the process running look at the jobs jobsYou will see it displayed. You can detach it with the "disown" command.Now to deal with HUP. Use "nohup."=== Terminate execution of script on command error ===While your shell script executes commands one might return a non-zero value. At the top of your shell script use set -eThis will cause the shell to exit immediately if a simple command exits with a nonzero exit value. A simple command is any command not part of an if, while, or until test, or part of an && or || list.Works with redirects too, such as command > output.txtDoes not work with pipes command | anothercommand parameterThe set -e directive is sometimes insufficient for example if you have pipes. If your script contains commands with pipes then include set -e set -o pipefailRather than the entire script under the influence of set -e you can use an exit on non-zero just on specific command lines in the script command || exit 1Or say you use to use a script wide set -e and exclude a particular line from causing the script to exit if that one particular command fails badcommand || trueEven if badcommand exits non-zero the script will go on, while set -e was specified at the top. The || true will make the command pipeline have a true return value even if the command fails so the the -e option will not kill the script.On errors, you can also use 'trap' with the pseudo-signal ERR=== See Also... ===* [[Advanced Shell Operations]] - The 2001 shell script example cookbook* [[How to write a shell script]] - Read before looking at examples* [[Regular Expressions Tutorial]] - RegEx is the real power in the shell script