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Delete Empty Directories
Deletes empty directories and prints an error if directory is not empty.

Write comments to your history.
A null operation with the name 'comment', allowing comments to be written to HISTFILE. Prepending '#' to a command will *not* write the command to the history file, although it will be available for the current session, thus '#' is not useful for keeping track of comments past the current session.

display typedefs, structs, unions and functions provided by a header file
will display typedefs, structs, unions and functions declared in 'stdio.h'(checkout _IO_FILE structure). It will be helpful if we want to know what a particular header file will offer to us. Command 'cpp' is GNU's C Preprocessor.

Convert tab separate file (TSV) to JSON with jq
With this command you can convert a tab separate file (TSV) into a JSON file with jq. For example, this input.tsv i-0b9adca882e5e6326 172.16.0.188 i-088dd69e5c3624888 172.16.0.102 i-0e70eac180537d4aa 172.16.0.85 will produce the showed output.

Edit the /etc/sudoers config file the right way.
'visudo' is installed by default on most Unix-like systems. If not installed, you can get it from the 'sudo' package. 'visudo' will use the text editor found in your $EDITOR variable, whether it's vi, vim, emacs, nano or gedit. After making changes to the /etc/sudoers file, visudo will check for syntax errors, and notify you of them. This is better than 'vi /etc/sudoers', because of this capability. Rule #1 of system administration- if there is a tool that exists for editing config files, use the tool.

run a command from within vi without exiting
":! ls -l " results in listing the files in the current directory. pressing "enter" will get you back into vi.

Search for in which package the specified file is included.

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" }

archlinux:Delete packages from pacman cache that are older than 7 days
Sometimes my /var/cache/pacman/pkg directory gets quite big in size. If that happens I run this command to remove old package files. Packages that we're upgraded in last N days are kept in case you are forced to downgrade a specific package. The command is obviously Arch Linux related.


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