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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" }

create an uncompressed tar file of each child directory of the current working directory
First, use find to find directories exactly one level below current directory, then create a tar file using the directory as the basename.

check open ports without netstat or lsof

Run a command for blocks of output of another command
The given example collects output of the tail command: Whenever a line is emitted, further lines are collected, until no more output comes for one second. This group of lines is then sent as notification to the user. You can test the example with $ logger "First group"; sleep 1; logger "Second"; logger "group"

Copy all files. All normal files, all hidden files and all files starting with - (minus).
./* is for copying files starting with - .[!.]* is for copying hidden files and avoiding copying files from the parent directory. ..?* is for copying files starting with .. (avoids the directory ..) /path/to/dir the path to the directory where the files should be copied Can also be used as a script. Input argument is /path/to/dir in tcsh, replace .[!.]* with .[^.]*

MSDOS command to check existance of command and exit batch if failed
This is a command to be used inside of MS-DOS batch files to check existence of commands as preconditions before actual batch processing can be started. If the command is found, batch script continues execution. If not, a message is printed on screen, script then waits for user pressing a key and exits. An error message of the command itself is suppressed for clarity purpose.

Figure out what shell you're running
short, sweet, and works after sudoing a new shell.

Generate hash( of some types) from string
No need to install yet another program when openssl is already installed. :-)

Grep by paragraph instead of by line.
This is a command that I find myself using all the time. It works like regular grep, but returns the paragraph containing the search pattern instead of just the line. It operates on files or standard input. $ grepp or $ | grepp

Create a file of repeated, non-zero
dd can be used with /dev/zero to easily create a file of all zero-bytes. Pipe that through tr and use octal conversions to change the byte values from zero to 0xff (octal 0377). You can replace 0377 with the byte of your choice. You can also use \\0 and \\377 instead of the quoted version.

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