Commands by Karakh (2)

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Tune your guitar from the command line.
This command, taken from play's manual page, plays a synthesized guitar tone for each of the strings on a standard tuned guitar. The command "play" is a part of the package "sox".

Unix alias for date command that lets you create timestamps in ISO 8601 format
I often need to add a timestamp to a file, but I never seem to remember the exact format string that has to be passed to the date command to get a compact datetime string like 20090220T231410 (i.e yyyymmddThhmmss, the ISO 8601 format popular outside the US)

Show directories in the PATH, one per line
The output of "echo $PATH" is hard to read, this is much easier. The parentheses ensure that the change to the input field separator (IFS) only happens the the sub shell and not affecting the current shell.

Rip a DVD to AVI format
Substitute whatever track number you want into the "dvd://1" parameter. The "-aid 128" is to select the English language.

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" }

tcpdump sniff pop3,imap,smtp and http

tail: watch a filelog
-f file(s) to be monitorized -n number of last line to be printed on the screen in this example, the content of two files are displayed

find file/dir by excluding some unwanted dirs and filesystems
Consider using this cmd when: 1. You are planning to traverse a big directory. 2. There is a subdir you don't want find to decend to. (entirely ignore) 3. You don't want find to decend to any mounted filesystems under this dir. * The -xdev flag tells find do not go to other filesystems. * -path ./junk_dir -prune is the pattern to ignore ./junk_dir entirely. * The rest is the typical search and print. To ignore multiple subdirs, you can just iterate the pattern, e.g. find . -path ./junk1 -prune -o -path ./junk2 -prune ... If you do want to include other filesystems, then remove -xdev flag. If you want to search files, then change -type d to -type f.

Check a directory of PNG files for errors
Useful for checking if a large number of PNG files was downloaded successfully by verifying the built-in CRC checksum. For incomplete files, the command will print: "00002309.png EOF while reading IDAT data ERROR: 00002309.png" The process is very fast; checking 21,000 files of 5MB in size took only five minutes on a 2011 Intel mobile dual-core.

Convert encoding of given files from one encoding to another


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