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Mapreduce style processing
parallel can be installed on your central node and can be used to run a command multiple times. In this example, multiple ssh connections are used to run commands. (-j is the number of jobs to run at the same time). The result can then be piped to commands to perform the "reduce" stage. (sort then uniq in this example). This example assumes "keyless ssh login" has been set up between the central node and all machines in the cluster. bashreduce may also do what you want.

32 bits or 64 bits?

create random string from /dev/urandom (or another length)

Transfer SSH public key to another machine in one step
This command sequence allows simple setup of (gasp!) password-less SSH logins. Be careful, as if you already have an SSH keypair in your ~/.ssh directory on the local machine, there is a possibility ssh-keygen may overwrite them. ssh-copy-id copies the public key to the remote host and appends it to the remote account's ~/.ssh/authorized_keys file. When trying ssh, if you used no passphrase for your key, the remote shell appears soon after invoking ssh [email protected]

Remove executable bit from all files in the current directory recursively, excluding other directories
Useful if you have copied files from an OS without a permission structure (for example, DOS) and you need to disable all executable files but want to be able to descend into your directories.

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" }

Pretty Print a simple csv in the command line
Will handle pretty much all types of CSV Files. The ^M character is typed on the command line using Ctrl-V Ctrl-M and can be replaced with any character that does not appear inside the CSV. Tips for simpler CSV files: * If newlines are not placed within a csv cell then you can replace `map(repr, r)` with r

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Cleanup a (source) text file, removing trailing spaces/tabs and multiple consecutive blank lines
I used this command (in addition to a code formatting tool) to "cleanup" a bunch of PHP files

Rotate a pdf by 90 degrees CW


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