Problem with cut

jnojr · 12-24-2009, 11:02 AM

I want to perform an action when swap is being used too heavily. My first thought was to use free, grep for "Swap:", and cut the column that shows how much is being used. But that just isn't happening.

The man page for cut says that TAB is the default delimiter, but:

Quote:

[jnojr@netcentric ~]$ free | grep Swap | cut -f4
Swap: 8388600 3198076 5190524

I tried adding the tab character specifically a couple of ways:

Quote:

[jnojr@netcentric ~]$ free | grep Swap | cut -d'' -f4
cut: the delimiter must be a single character
Try `cut --help' for more information.

(That was single-quote, TAB, single-quote)

Quote:

[jnojr@netcentric ~]$ free | grep Swap | cut -d$'\t' -f4
Swap: 8388600 3193524 5195076

I suppose it's possible that free isn't using a tab character to format the output, but that doesn't make a lot of sense to me.

catkin · 12-24-2009, 11:16 AM

Quote:

Originally Posted by jnojr

I suppose it's possible that free isn't using a tab character to format the output, but that doesn't make a lot of sense to me.

free doesn't use tabs. I just confirmed it by free > free.out and examining the output file in vim.

It's a rational design choice because there is no way to know what the tab setting is on all possible output "media". I think it's the same for most commands.

jnojr · 12-24-2009, 11:39 AM

Criminy.

Well, since cut doesn't have a setting to consider "any/all whitespace" as a delimiter, and there's no way to know in advance how many spaces it'll use...

catkin · 12-24-2009, 11:59 AM

Not easily but you could use a tool that regards multiple spaces as a single field separator such as awk or the shell itself.

Code:

array=( $(free) )
echo "Swap used is ${array[19]}"

evo2 · 12-24-2009, 01:27 PM

Just hitting tab on the command line generally wont work because your shell will grab it and try interpret it as a completion request. You can enter literal characters on the command line by first typing Ctrl-V.

HTH,

Evo2.

PS. In regard to your actual question ,I'm pretty sure that the output of free is just padded with multiple spaces.