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| * How can I ensure that only once instance of my script is running at a time? * Answer: e.g. lockfile. This should be answered in the UnixFaq * It's also [[BashFAQ#faq45|Bash FAQ #45]] now. * It's also covered in ProcessManagement. * How can I handle command line arguments in a shell script? * {{{getopts}}}, or a while/shift loop (see [[BashFAQ#faq35|Bash FAQ #35]]) * How can I have variable variables, e.g. myvar=prefix$othervar? * Answer: {{{eval}}} -- see also [[BashFAQ#faq6|Bash FAQ #6]] and the warnings in [[BashFAQ#faq48|#48]]. * If {{{othervar}}} is an integer, use an [[BashFAQ#faq5|array]] instead. |
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| * In bash 4, the DEBUG trap is triggered ''before'' every command, according to `help trap`. This is a change from bash 3. So this should be possible in bash 4. Someone just needs to write it up.... | |
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| * date -d'yesterday' # GNU date | * date -d'yesterday' # GNU date (sufficiently new versions) * date -d '1 day ago' # GNU date (all versions I have available to test) |
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| * How to convert Unix time stamps to a date (and vice versa)? * [[BashFAQ#faq70|FAQ #70]] * How to redirect stderr to a pipeline? Now [[BashFAQ#faq47|Bash FAQ #47]] * command 2>&1 | command * To discard stdout entirely: command 2>&1 >/dev/null | command |
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| * i think this does the job, have not had time to test: http://tldp.org/LDP/abs/html/process-sub.html Commands in a process substitution ( >(cmd) or <(cmd) ) are definitely run in a subshell. I'm not sure I understand what this question is really asking. Maybe it's related to [[BashFAQ#faq84|FAQ 84]]. |
* I think this does the job, have not had time to test: http://tldp.org/LDP/abs/html/process-sub.html (see also ProcessSubstitution on this site) * Commands in a process substitution ( >(cmd) or <(cmd) ) are definitely run in a subshell (or rather a full-blown background process). I'm not sure I understand what this question is really asking. Maybe it's related to [[BashFAQ/084|FAQ 84]]. * Creating temporary files securely and ''portably'' ([[BashFAQ/062]] has a partial answer) |
Bash Open Questions
If you want to help with the BashFAQ, you could try to answer one of the following questions. Just answer it, copy it to a new subpage of the BashFAQ page (e.g. BashFAQ/101), and remove the question here.
- How can I redirect the output of the script to both standard output and a log file?
- Duplicating fds is not sufficient, because it duplicates the file descriptor number, not the data.
But you can still use tee: exec > >(tee log)
- Somewhere the content of variables in my script lose whitespace.
echo "$var" - quoting. See BashPitfalls for more.
- How can I make bash set the xterm title to the command it is currently executing?
- This can't be done in any straightforward manner because there's no hook in Bash to execute arbitrary code after a user presses Enter but before a command is executed. The DEBUG trap is triggered after each command, and the PS1 variable is triggered when a prompt is displayed, which is also after the command, rather than before.
In bash 4, the DEBUG trap is triggered before every command, according to help trap. This is a change from bash 3. So this should be possible in bash 4. Someone just needs to write it up....
- How to determine Yesterday's date?
- date -d'yesterday' # GNU date (sufficiently new versions)
- date -d '1 day ago' # GNU date (all versions I have available to test)
- date -r $(( $(date +%s) - 86400 )) # OpenBSD date
- How can I redirect file names using sequential numbers to avoid overwriting existing ones?
- mv --backup=numbered # requires GNU mv
- How can I set the output of a command to a variable without executing a subshell (i.e. $() ) or writing to a file and reading it back?
I think this does the job, have not had time to test: http://tldp.org/LDP/abs/html/process-sub.html (see also ProcessSubstitution on this site)
Commands in a process substitution ( >(cmd) or <(cmd) ) are definitely run in a subshell (or rather a full-blown background process). I'm not sure I understand what this question is really asking. Maybe it's related to FAQ 84.
Creating temporary files securely and portably (BashFAQ/062 has a partial answer)