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Fri, Feb 28, 2014 10:41 pm

Using awk to sum numbers in a file

The awk command found on Linux/Unix and Mac OS X systems can be used to sum numbers in a file. E.g., suppose the file numbers.txt contains the following numbers:

The contents of the file can be piped into the awk command with the cat command and then summed by awk.

$ cat numbers.txt | awk '{sum+=$1} END {print sum}'

If the numbers are not in the first column in the file, but were in the second column instead, you can adjust $1 to be the relevant column instead. E.g, if the file contents looked like the following with the numbers in the second column, then you would use $2 instead.

Dave 10
Bill 20
Joe 30
Mary 40
Maria 50
Howard 1
Sam 2
Lisa 3
Karen 4
Nina 5
$ cat numbers.txt | awk '{sum+=$2} END {print sum}'

If you know the numbers always occur in specific colum positions in the file, e.g., in positions 10 to 15, you could also use the cut command instead of the cat command. E.g., if you file contained:

Dave     10
Bill     20
Joe      30
Mary     40
Maria    50
Howard    1
Sam       2
Lisa      3
Karen     4
Nina      5
$ cut -c10-11 numbers.txt | awk '{sum+=$1} END {print sum}'

[/os/unix/commands] permanent link

Fri, Feb 28, 2014 10:09 pm

Managing Wi-Fi from the terminal command line under OS X

To manage Wi-Fi connections from a shell prompt on a Mac OS X system you can obtain a command line interface by running the Terminal program located in Applications/Utilities. From that command line interface, you can determine whether a WiFi interface is present on the system using the command networksetup -listallnetworkservices. You should see "Wi-Fi" in the list of services that appears when you issue the command.
$ networksetup -listallnetworkservices
An asterisk (*) denotes that a network service is disabled.
Bluetooth DUN

To determine the hardware interface supporting Wi-Fi connections you can use the command networksetup -listallhardwareports.

$ networksetup -listallhardwareports

Hardware Port: Bluetooth DUN
Device: Bluetooth-Modem
Ethernet Address: N/A

Hardware Port: Ethernet
Device: en0
Ethernet Address: d4:9a:20:0d:e6:ec

Hardware Port: FireWire
Device: fw0
Ethernet Address: d4:9a:20:ff:fe:0d:e6:ec

Hardware Port: Wi-Fi
Device: en1
Ethernet Address: f8:1e:df:d9:2b:66

VLAN Configurations

In the case above, the Wi-Fi interface is en1.

To get information on the status of the system's Wi-Fi connection, you can use the command networksetup -getinfo Wi-Fi.

$ networksetup -getinfo Wi-Fi
DHCP Configuration
IP address:
Subnet mask:
Client ID: 
IPv6: Automatic
IPv6 IP address: none
IPv6 Router: none
Wi-Fi ID: f8:1e:df:d9:2b:66

To find if the system is currently connected to a wireless network and the network name for the current wireless connection, you can use networksetup -getairportnetwork <device name> where device name is the network interface on the system that supports WiFi connections. E.g.:

$ networksetup -getairportnetwork en1
Current Wi-Fi Network: Copernicus

If you stipulate a network interface that is not a WiFi interface, you will get an error message indicating the interface is not a Wi-Fi interface as shown below:

$ networksetup -getairportnetwork en0
en0 is not a Wi-Fi interface.
** Error: Error obtaining wireless information.

If you wish to to turn the Wi-Fi connection on or off from a shell prompt, you can use the networksetup -setairportnetwork command.

networksetup -setairportnetwork <device name> <network> [password]
$ networksetup -setairportpower en1 off
$ networksetup -getairportnetwork en1
You are not associated with an AirPort network.
Wi-Fi power is currently off.
$ networksetup -setairportpower en1 on
$ networksetup -getairportnetwork en1
Current Wi-Fi Network: Copernicus

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