Commands tagged trap (4)

  • Changing the terminal title to the last shell command

    You can set the previous bash command as the terminal title by this command. Explanation: -trap assigns a command to execute at a given bash signal. -in the $BASH_COMMAND you find the last command -you can set the terminal title with the escape sequence: \e]0;this is the title\007 -to let the echo care about the backslashes give the -e to it Since trap is a built in bash command you find more informatin in 'man bash'for more Source: http://www.davidpashley.com/articles/xterm-titles-with-bash.html


    8
    trap 'echo -e "\e]0;$BASH_COMMAND\007"' DEBUG
    Vereb · 2009-09-29 21:09:21 18
  • Cleanly manage tempfiles in scripts

    Cleanly create tempfiles using mktemp and remove them using traps instead of removing them in the end of the script. This way, you make sure the tempfiles are removed properly even if the script is killed or interrupted. For a user script in KDE4, you can set TMPROOT using : TMPROOT=$(kde4-config --path tmp)


    3
    TMPROOT=/tmp; TMPDIR=$(mktemp -d $TMPROOT/somedir.XXXXXX); TMPFILE=$(mktemp $TMPROOT/somefile.XXXXXX); trap "rm -rf $TMPDIR $TMPFILE; exit" INT TERM EXIT; some treatment using $TMPDIR and $TMPFILE; exit 0
    raphink · 2009-02-24 09:35:22 5
  • Schedule Nice Background Commands That Won't Die on Logout - Alternative to nohup and at

    Check out the usage of 'trap', you may not have seen this one much. This command provides a way to schedule commands at certain times by running them after sleep finishes sleeping. In the example 'sleep 2h' sleeps for 2 hours. What is cool about this command is that it uses the 'trap' builtin bash command to remove the SIGHUP trap that normally exits all processes started by the shell upon logout. The 'trap 1' command then restores the normal SIGHUP behaviour. It also uses the 'nice -n 19' command which causes the sleep process to be run with minimal CPU. Further, it runs all the commands within the 2nd parentheses in the background. This is sweet cuz you can fire off as many of these as you want. Very helpful for shell scripts.


    2
    ( trap '' 1; ( nice -n 19 sleep 2h && command rm -v -rf /garbage/ &>/dev/null && trap 1 ) & )
    AskApache · 2009-10-10 04:43:44 7
  • Collect output from a segfaulting program and keep the script from dying

    Crash Override, man! Apparently the exec call tricks BASH into setting the output buffer size to 0 under the assumption that the system (or the calling shell) will handle the output buffering. trapping the ERR signal will stop the subshell from dying and sending the ERR signal to the main script--which will terminate immediately if it does--when the program fails. The only problem is that the kernel will output a whole bunch of stack trace garbage directly to the console device once the process segfaults, so there's no way to prevent it from being output [that I know of].


    0
    (trap 'true' ERR; exec <SEGFAULT_PRONE_PROGRAM>)
    h3xx · 2011-07-25 02:30:52 4

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Stoppable sleep
A nice way to interrupt a sleep with a signal.

Copy an element from the previous command
'n' is a non-negative integer. Using 0 will expand to the name of the previous command.

Annoying PROMPT_COMMAND animation
unset PROMPT_COMMAND to disable.

Use /dev/full to test language I/O-failsafety
The Linux /dev/full file simulates a "disk full" condition, and can be used to verify how a program handles this situation. In particular, several programming language implementations do not print error diagnostics (nor exit with error status) when I/O errors like this occur, unless the programmer has taken additional steps. That is, simple code in these languages does not fail safely. In addition to Perl, C, C++, Tcl, and Lua (for some functions) also appear not to fail safely.

Remove color codes (special characters) with sed
Removes ANSI color and end of line codes to the [{attr1};...;{attrn}m format.

Terminal Escape Code Zen - Strace and Tput
Depending on the TERM, the terminfo version, ncurses version, etc.. you may be using a varied assortment of terminal escape codes. With this command you can easily find out exactly what is going on.. This is terminal escape zen! $ ( 2>&2 strace -f -F -e write -s 1000 sh -c 'echo -e "initc\nis2\ncnorm\nrmso\nsgr0" | tput -S' 2>&1 ) | grep -o '"\\[^"]*"' --color=always "\33]4;%p1%d;rgb:%p2%{255}%*%{1000}%/%2.2X/%p3%{255}%*%{1000}%/%2.2X/%p4%{255}%*%{1000}%/%2.2X\33\\\33[!p\33[?3;4l\33[4l\33>\33[?12l\33[?25h\33[27m\33(B\33[m" Lets say you want to find out what you need to echo in order to get the text to blink.. $ echo -e "`tput blink`This will blink`tput sgr0` This wont" Now you can use this function instead of calling tput (tput is much smarter for portable code because it works differently depending on the current TERM, and tput -T anyterm works too.) to turn that echo into a much faster executing code. tput queries files, opens files, etc.. but echo is very strait and narrow. So now you can do this: $ echo -e "\33[5mThis will blink\33(B\33[m This wont" More at http://www.askapache.com/linux-unix/bash_profile-functions-advanced-shell.html

Show a curses based menu selector
Not so much handy by itself, but very nice in shell scripts. This makes you a handy ncurses based checklist. Much like terminal installers, just use the arrow keys and hit 'Space' to adjust the selections. Returns all selected tags as strings, with no newline at the end. So, your output will be something like: "one" "two" "three" "four" "etc" For those who prefer bash expansion over gratuitious typing: $ whiptail --checklist "Simple checkbox menu" 12 35 3 $(echo {one,two,three,four}" '' 0"} ) Things to note: The height must includes the outer border and padding: add 7 to however many items you want to show up at the same time. If the status is 1, it will be selected by default. anything else, will be deselected.

Convert seconds to [DD:][HH:]MM:SS
Converts any number of seconds into days, hours, minutes and seconds. sec2dhms() { declare -i SS="$1" D=$(( SS / 86400 )) H=$(( SS % 86400 / 3600 )) M=$(( SS % 3600 / 60 )) S=$(( SS % 60 )) [ "$D" -gt 0 ] && echo -n "${D}:" [ "$H" -gt 0 ] && printf "%02g:" "$H" printf "%02g:%02g\n" "$M" "$S" }

Which processes are listening on a specific port (e.g. port 80)
swap out "80" for your port of interest. Can use port number or named ports e.g. "http"

Convert seconds to [DD:][HH:]MM:SS
Converts any number of seconds into days, hours, minutes and seconds. sec2dhms() { declare -i SS="$1" D=$(( SS / 86400 )) H=$(( SS % 86400 / 3600 )) M=$(( SS % 3600 / 60 )) S=$(( SS % 60 )) [ "$D" -gt 0 ] && echo -n "${D}:" [ "$H" -gt 0 ] && printf "%02g:" "$H" printf "%02g:%02g\n" "$M" "$S" }

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