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get stdout to variable and stdout at sametime
Sometimes you want to write the script output to stdout but you need to send it to email. If you use: $ var="$( ls / )"; $ echo -e "$var"; works but, you need to wait the script terminate to bufferize then print the output var; With this way, you can use/work/print the output before the variable receive all the output content, then after it you can use the variable for anything else, like send email.

Randomize lines in a file
Works in sort (GNU coreutils) 7.4, don't know when it was implemented but sometime the last 6 years.

list block devices
Shows all block devices in a tree with descruptions of what they are.

Replaces a color in a PDF document, useful for removing a dark background before printing.
The pdf is first converted to a bitmap, so change "-density" to match your printer resolution. Also be careful about the RAM required. In this example rgb(0,0,0) is replaced by rgb(255,255,255), change to suit your needs.

Transfer large files/directories with no overhead over the network
This invokes tar on the remote machine and pipes the resulting tarfile over the network using ssh and is saved on the local machine. This is useful for making a one-off backup of a directory tree with zero storage overhead on the source. Variations on this include using compression on the source by using 'tar cfvp' or compression at the destination via $ ssh user@host "cd dir; tar cfp - *" | gzip - > file.tar.gz

Instant mirror from your laptop + webcam
Flips the y-axis to emulate a real mirror, uses low resolution for speed, this will also hide blemishes and the like :)

Easily decode unix-time (funtion)
A shell function using perl to easily convert Unix-time to text. Put in in your ~/.bashrc or equivalent. Tested on Linux / Solaris Bourne, bash and zsh. using perl 5.6 and higher. (Does not require GNU date like some other commands)

Create POSIX tar archive
tar(1) and cpio(1) are not fully platform agnostic, although their file formats are specified in POSIX.1-2001. As such, GNU tar(1) might not be able to extract a BSD tar(1) archive, and ivce versa. pax(1) is defined in POSIX.1-2001. To extract an archive: $ pax -rf archive.tar

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" }

back ssh from firewalled hosts
host B (you) redirects a modem port (62220) to his local ssh. host A is a remote machine (the ones that issues the ssh cmd). once connected port 5497 is in listening mode on host B. host B just do a ssh 127.0.0.1 -p 5497 -l user and reaches the remote host'ssh. This can be used also for vnc and so on.


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